diff --git a/libbacktrace/UnwindStack.cpp b/libbacktrace/UnwindStack.cpp
index 3a38839..d61384e 100644
--- a/libbacktrace/UnwindStack.cpp
+++ b/libbacktrace/UnwindStack.cpp
@@ -99,8 +99,7 @@
     // one extra function call appearing in the unwind.
     unwindstack::RegsGetLocal(regs.get());
   } else {
-    regs.reset(
-        unwindstack::Regs::CreateFromUcontext(unwindstack::Regs::CurrentMachineType(), ucontext));
+    regs.reset(unwindstack::Regs::CreateFromUcontext(unwindstack::Regs::CurrentArch(), ucontext));
   }
 
   error_ = BACKTRACE_UNWIND_NO_ERROR;
@@ -120,8 +119,7 @@
   if (context == nullptr) {
     regs.reset(unwindstack::Regs::RemoteGet(Tid()));
   } else {
-    regs.reset(
-        unwindstack::Regs::CreateFromUcontext(unwindstack::Regs::CurrentMachineType(), context));
+    regs.reset(unwindstack::Regs::CreateFromUcontext(unwindstack::Regs::CurrentArch(), context));
   }
 
   error_ = BACKTRACE_UNWIND_NO_ERROR;
diff --git a/libunwindstack/Android.bp b/libunwindstack/Android.bp
index 74930d6..4125b12 100644
--- a/libunwindstack/Android.bp
+++ b/libunwindstack/Android.bp
@@ -60,6 +60,10 @@
         "Maps.cpp",
         "Memory.cpp",
         "Regs.cpp",
+        "RegsArm.cpp",
+        "RegsArm64.cpp",
+        "RegsX86.cpp",
+        "RegsX86_64.cpp",
         "Unwinder.cpp",
         "Symbols.cpp",
     ],
diff --git a/libunwindstack/ArmExidx.cpp b/libunwindstack/ArmExidx.cpp
index fed3e0e..6b0646f 100644
--- a/libunwindstack/ArmExidx.cpp
+++ b/libunwindstack/ArmExidx.cpp
@@ -23,11 +23,11 @@
 
 #include <unwindstack/Log.h>
 #include <unwindstack/Memory.h>
-#include <unwindstack/Regs.h>
+#include <unwindstack/RegsArm.h>
 
 #include "ArmExidx.h"
 #include "Check.h"
-#include "Machine.h"
+#include "MachineArm.h"
 
 namespace unwindstack {
 
diff --git a/libunwindstack/Elf.cpp b/libunwindstack/Elf.cpp
index 5f307ed..025429f 100644
--- a/libunwindstack/Elf.cpp
+++ b/libunwindstack/Elf.cpp
@@ -31,7 +31,6 @@
 #include <unwindstack/Regs.h>
 
 #include "ElfInterfaceArm.h"
-#include "Machine.h"
 #include "Symbols.h"
 
 namespace unwindstack {
@@ -183,18 +182,15 @@
       return nullptr;
     }
 
-    if (e_machine != EM_ARM && e_machine != EM_386) {
-      // Unsupported.
-      ALOGI("32 bit elf that is neither arm nor x86: e_machine = %d\n", e_machine);
-      return nullptr;
-    }
-
     machine_type_ = e_machine;
     if (e_machine == EM_ARM) {
+      arch_ = ARCH_ARM;
       interface.reset(new ElfInterfaceArm(memory));
     } else if (e_machine == EM_386) {
+      arch_ = ARCH_X86;
       interface.reset(new ElfInterface32(memory));
     } else {
+      // Unsupported.
       ALOGI("32 bit elf that is neither arm nor x86: e_machine = %d\n", e_machine);
       return nullptr;
     }
@@ -203,12 +199,17 @@
     if (!memory->ReadFully(EI_NIDENT + sizeof(Elf64_Half), &e_machine, sizeof(e_machine))) {
       return nullptr;
     }
-    if (e_machine != EM_AARCH64 && e_machine != EM_X86_64) {
+
+    machine_type_ = e_machine;
+    if (e_machine == EM_AARCH64) {
+      arch_ = ARCH_ARM64;
+    } else if (e_machine == EM_X86_64) {
+      arch_ = ARCH_X86_64;
+    } else {
       // Unsupported.
       ALOGI("64 bit elf that is neither aarch64 nor x86_64: e_machine = %d\n", e_machine);
       return nullptr;
     }
-    machine_type_ = e_machine;
     interface.reset(new ElfInterface64(memory));
   }
 
diff --git a/libunwindstack/ElfInterfaceArm.cpp b/libunwindstack/ElfInterfaceArm.cpp
index 170a5cd..9841e24 100644
--- a/libunwindstack/ElfInterfaceArm.cpp
+++ b/libunwindstack/ElfInterfaceArm.cpp
@@ -18,11 +18,11 @@
 #include <stdint.h>
 
 #include <unwindstack/Memory.h>
-#include <unwindstack/Regs.h>
+#include <unwindstack/RegsArm.h>
 
 #include "ArmExidx.h"
 #include "ElfInterfaceArm.h"
-#include "Machine.h"
+#include "MachineArm.h"
 
 namespace unwindstack {
 
diff --git a/libunwindstack/Machine.h b/libunwindstack/Machine.h
deleted file mode 100644
index 1fb9309..0000000
--- a/libunwindstack/Machine.h
+++ /dev/null
@@ -1,141 +0,0 @@
-/*
- * Copyright (C) 2016 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#ifndef _LIBUNWINDSTACK_MACHINE_H
-#define _LIBUNWINDSTACK_MACHINE_H
-
-#include <stdint.h>
-
-namespace unwindstack {
-
-enum ArmReg : uint16_t {
-  ARM_REG_R0 = 0,
-  ARM_REG_R1,
-  ARM_REG_R2,
-  ARM_REG_R3,
-  ARM_REG_R4,
-  ARM_REG_R5,
-  ARM_REG_R6,
-  ARM_REG_R7,
-  ARM_REG_R8,
-  ARM_REG_R9,
-  ARM_REG_R10,
-  ARM_REG_R11,
-  ARM_REG_R12,
-  ARM_REG_R13,
-  ARM_REG_R14,
-  ARM_REG_R15,
-  ARM_REG_LAST,
-
-  ARM_REG_SP = ARM_REG_R13,
-  ARM_REG_LR = ARM_REG_R14,
-  ARM_REG_PC = ARM_REG_R15,
-};
-
-enum Arm64Reg : uint16_t {
-  ARM64_REG_R0 = 0,
-  ARM64_REG_R1,
-  ARM64_REG_R2,
-  ARM64_REG_R3,
-  ARM64_REG_R4,
-  ARM64_REG_R5,
-  ARM64_REG_R6,
-  ARM64_REG_R7,
-  ARM64_REG_R8,
-  ARM64_REG_R9,
-  ARM64_REG_R10,
-  ARM64_REG_R11,
-  ARM64_REG_R12,
-  ARM64_REG_R13,
-  ARM64_REG_R14,
-  ARM64_REG_R15,
-  ARM64_REG_R16,
-  ARM64_REG_R17,
-  ARM64_REG_R18,
-  ARM64_REG_R19,
-  ARM64_REG_R20,
-  ARM64_REG_R21,
-  ARM64_REG_R22,
-  ARM64_REG_R23,
-  ARM64_REG_R24,
-  ARM64_REG_R25,
-  ARM64_REG_R26,
-  ARM64_REG_R27,
-  ARM64_REG_R28,
-  ARM64_REG_R29,
-  ARM64_REG_R30,
-  ARM64_REG_R31,
-  ARM64_REG_PC,
-  ARM64_REG_LAST,
-
-  ARM64_REG_SP = ARM64_REG_R31,
-  ARM64_REG_LR = ARM64_REG_R30,
-};
-
-// Matches the numbers for the registers as generated by compilers.
-// If this is changed, then unwinding will fail.
-enum X86Reg : uint16_t {
-  X86_REG_EAX = 0,
-  X86_REG_ECX = 1,
-  X86_REG_EDX = 2,
-  X86_REG_EBX = 3,
-  X86_REG_ESP = 4,
-  X86_REG_EBP = 5,
-  X86_REG_ESI = 6,
-  X86_REG_EDI = 7,
-  X86_REG_EIP = 8,
-  X86_REG_EFL = 9,
-  X86_REG_CS = 10,
-  X86_REG_SS = 11,
-  X86_REG_DS = 12,
-  X86_REG_ES = 13,
-  X86_REG_FS = 14,
-  X86_REG_GS = 15,
-  X86_REG_LAST,
-
-  X86_REG_SP = X86_REG_ESP,
-  X86_REG_PC = X86_REG_EIP,
-};
-
-// Matches the numbers for the registers as generated by compilers.
-// If this is changed, then unwinding will fail.
-enum X86_64Reg : uint16_t {
-  X86_64_REG_RAX = 0,
-  X86_64_REG_RDX = 1,
-  X86_64_REG_RCX = 2,
-  X86_64_REG_RBX = 3,
-  X86_64_REG_RSI = 4,
-  X86_64_REG_RDI = 5,
-  X86_64_REG_RBP = 6,
-  X86_64_REG_RSP = 7,
-  X86_64_REG_R8 = 8,
-  X86_64_REG_R9 = 9,
-  X86_64_REG_R10 = 10,
-  X86_64_REG_R11 = 11,
-  X86_64_REG_R12 = 12,
-  X86_64_REG_R13 = 13,
-  X86_64_REG_R14 = 14,
-  X86_64_REG_R15 = 15,
-  X86_64_REG_RIP = 16,
-  X86_64_REG_LAST,
-
-  X86_64_REG_SP = X86_64_REG_RSP,
-  X86_64_REG_PC = X86_64_REG_RIP,
-};
-
-}  // namespace unwindstack
-
-#endif  // _LIBUNWINDSTACK_MACHINE_H
diff --git a/libunwindstack/MachineArm.h b/libunwindstack/MachineArm.h
new file mode 100644
index 0000000..3f902b1
--- /dev/null
+++ b/libunwindstack/MachineArm.h
@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBUNWINDSTACK_MACHINE_ARM_H
+#define _LIBUNWINDSTACK_MACHINE_ARM_H
+
+#include <stdint.h>
+
+namespace unwindstack {
+
+enum ArmReg : uint16_t {
+  ARM_REG_R0 = 0,
+  ARM_REG_R1,
+  ARM_REG_R2,
+  ARM_REG_R3,
+  ARM_REG_R4,
+  ARM_REG_R5,
+  ARM_REG_R6,
+  ARM_REG_R7,
+  ARM_REG_R8,
+  ARM_REG_R9,
+  ARM_REG_R10,
+  ARM_REG_R11,
+  ARM_REG_R12,
+  ARM_REG_R13,
+  ARM_REG_R14,
+  ARM_REG_R15,
+  ARM_REG_LAST,
+
+  ARM_REG_SP = ARM_REG_R13,
+  ARM_REG_LR = ARM_REG_R14,
+  ARM_REG_PC = ARM_REG_R15,
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_MACHINE_ARM_H
diff --git a/libunwindstack/MachineArm64.h b/libunwindstack/MachineArm64.h
new file mode 100644
index 0000000..e8b778b
--- /dev/null
+++ b/libunwindstack/MachineArm64.h
@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBUNWINDSTACK_MACHINE_ARM64_H
+#define _LIBUNWINDSTACK_MACHINE_ARM64_H
+
+#include <stdint.h>
+
+namespace unwindstack {
+
+enum Arm64Reg : uint16_t {
+  ARM64_REG_R0 = 0,
+  ARM64_REG_R1,
+  ARM64_REG_R2,
+  ARM64_REG_R3,
+  ARM64_REG_R4,
+  ARM64_REG_R5,
+  ARM64_REG_R6,
+  ARM64_REG_R7,
+  ARM64_REG_R8,
+  ARM64_REG_R9,
+  ARM64_REG_R10,
+  ARM64_REG_R11,
+  ARM64_REG_R12,
+  ARM64_REG_R13,
+  ARM64_REG_R14,
+  ARM64_REG_R15,
+  ARM64_REG_R16,
+  ARM64_REG_R17,
+  ARM64_REG_R18,
+  ARM64_REG_R19,
+  ARM64_REG_R20,
+  ARM64_REG_R21,
+  ARM64_REG_R22,
+  ARM64_REG_R23,
+  ARM64_REG_R24,
+  ARM64_REG_R25,
+  ARM64_REG_R26,
+  ARM64_REG_R27,
+  ARM64_REG_R28,
+  ARM64_REG_R29,
+  ARM64_REG_R30,
+  ARM64_REG_R31,
+  ARM64_REG_PC,
+  ARM64_REG_LAST,
+
+  ARM64_REG_SP = ARM64_REG_R31,
+  ARM64_REG_LR = ARM64_REG_R30,
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_MACHINE_ARM64_H
diff --git a/libunwindstack/MachineX86.h b/libunwindstack/MachineX86.h
new file mode 100644
index 0000000..02adb98
--- /dev/null
+++ b/libunwindstack/MachineX86.h
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBUNWINDSTACK_MACHINE_X86_H
+#define _LIBUNWINDSTACK_MACHINE_X86_H
+
+#include <stdint.h>
+
+namespace unwindstack {
+
+// Matches the numbers for the registers as generated by compilers.
+// If this is changed, then unwinding will fail.
+enum X86Reg : uint16_t {
+  X86_REG_EAX = 0,
+  X86_REG_ECX = 1,
+  X86_REG_EDX = 2,
+  X86_REG_EBX = 3,
+  X86_REG_ESP = 4,
+  X86_REG_EBP = 5,
+  X86_REG_ESI = 6,
+  X86_REG_EDI = 7,
+  X86_REG_EIP = 8,
+  X86_REG_EFL = 9,
+  X86_REG_CS = 10,
+  X86_REG_SS = 11,
+  X86_REG_DS = 12,
+  X86_REG_ES = 13,
+  X86_REG_FS = 14,
+  X86_REG_GS = 15,
+  X86_REG_LAST,
+
+  X86_REG_SP = X86_REG_ESP,
+  X86_REG_PC = X86_REG_EIP,
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_MACHINE_X86_H
diff --git a/libunwindstack/MachineX86_64.h b/libunwindstack/MachineX86_64.h
new file mode 100644
index 0000000..af33fea
--- /dev/null
+++ b/libunwindstack/MachineX86_64.h
@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBUNWINDSTACK_MACHINE_X86_64_H
+#define _LIBUNWINDSTACK_MACHINE_X86_64_H
+
+#include <stdint.h>
+
+namespace unwindstack {
+
+// Matches the numbers for the registers as generated by compilers.
+// If this is changed, then unwinding will fail.
+enum X86_64Reg : uint16_t {
+  X86_64_REG_RAX = 0,
+  X86_64_REG_RDX = 1,
+  X86_64_REG_RCX = 2,
+  X86_64_REG_RBX = 3,
+  X86_64_REG_RSI = 4,
+  X86_64_REG_RDI = 5,
+  X86_64_REG_RBP = 6,
+  X86_64_REG_RSP = 7,
+  X86_64_REG_R8 = 8,
+  X86_64_REG_R9 = 9,
+  X86_64_REG_R10 = 10,
+  X86_64_REG_R11 = 11,
+  X86_64_REG_R12 = 12,
+  X86_64_REG_R13 = 13,
+  X86_64_REG_R14 = 14,
+  X86_64_REG_R15 = 15,
+  X86_64_REG_RIP = 16,
+  X86_64_REG_LAST,
+
+  X86_64_REG_SP = X86_64_REG_RSP,
+  X86_64_REG_PC = X86_64_REG_RIP,
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_MACHINE_X86_64_H
diff --git a/libunwindstack/Regs.cpp b/libunwindstack/Regs.cpp
index 28a77dc..29dbf9d 100644
--- a/libunwindstack/Regs.cpp
+++ b/libunwindstack/Regs.cpp
@@ -14,7 +14,6 @@
  * limitations under the License.
  */
 
-#include <elf.h>
 #include <stdint.h>
 #include <sys/ptrace.h>
 #include <sys/uio.h>
@@ -23,315 +22,21 @@
 
 #include <unwindstack/Elf.h>
 #include <unwindstack/MapInfo.h>
-#include <unwindstack/Memory.h>
 #include <unwindstack/Regs.h>
+#include <unwindstack/RegsArm.h>
+#include <unwindstack/RegsArm64.h>
+#include <unwindstack/RegsX86.h>
+#include <unwindstack/RegsX86_64.h>
 
-#include "Check.h"
-#include "Machine.h"
-#include "Ucontext.h"
-#include "User.h"
+#include "UserArm.h"
+#include "UserArm64.h"
+#include "UserX86.h"
+#include "UserX86_64.h"
 
 namespace unwindstack {
 
-RegsArm::RegsArm()
-    : RegsImpl<uint32_t>(ARM_REG_LAST, ARM_REG_SP, Location(LOCATION_REGISTER, ARM_REG_LR)) {}
-
-uint32_t RegsArm::MachineType() {
-  return EM_ARM;
-}
-
-uint64_t RegsArm::GetAdjustedPc(uint64_t rel_pc, Elf* elf) {
-  if (!elf->valid()) {
-    return rel_pc;
-  }
-
-  uint64_t load_bias = elf->GetLoadBias();
-  if (rel_pc < load_bias) {
-    return rel_pc;
-  }
-  uint64_t adjusted_rel_pc = rel_pc - load_bias;
-
-  if (adjusted_rel_pc < 5) {
-    return rel_pc;
-  }
-
-  if (adjusted_rel_pc & 1) {
-    // This is a thumb instruction, it could be 2 or 4 bytes.
-    uint32_t value;
-    if (rel_pc < 5 || !elf->memory()->ReadFully(adjusted_rel_pc - 5, &value, sizeof(value)) ||
-        (value & 0xe000f000) != 0xe000f000) {
-      return rel_pc - 2;
-    }
-  }
-  return rel_pc - 4;
-}
-
-void RegsArm::SetFromRaw() {
-  set_pc(regs_[ARM_REG_PC]);
-  set_sp(regs_[ARM_REG_SP]);
-}
-
-bool RegsArm::SetPcFromReturnAddress(Memory*) {
-  if (pc() == regs_[ARM_REG_LR]) {
-    return false;
-  }
-
-  set_pc(regs_[ARM_REG_LR]);
-  return true;
-}
-
-void RegsArm::IterateRegisters(std::function<void(const char*, uint64_t)> fn) {
-  fn("r0", regs_[ARM_REG_R0]);
-  fn("r1", regs_[ARM_REG_R1]);
-  fn("r2", regs_[ARM_REG_R2]);
-  fn("r3", regs_[ARM_REG_R3]);
-  fn("r4", regs_[ARM_REG_R4]);
-  fn("r5", regs_[ARM_REG_R5]);
-  fn("r6", regs_[ARM_REG_R6]);
-  fn("r7", regs_[ARM_REG_R7]);
-  fn("r8", regs_[ARM_REG_R8]);
-  fn("r9", regs_[ARM_REG_R9]);
-  fn("r10", regs_[ARM_REG_R10]);
-  fn("r11", regs_[ARM_REG_R11]);
-  fn("ip", regs_[ARM_REG_R12]);
-  fn("sp", regs_[ARM_REG_SP]);
-  fn("lr", regs_[ARM_REG_LR]);
-  fn("pc", regs_[ARM_REG_PC]);
-}
-
-RegsArm64::RegsArm64()
-    : RegsImpl<uint64_t>(ARM64_REG_LAST, ARM64_REG_SP, Location(LOCATION_REGISTER, ARM64_REG_LR)) {}
-
-uint32_t RegsArm64::MachineType() {
-  return EM_AARCH64;
-}
-
-uint64_t RegsArm64::GetAdjustedPc(uint64_t rel_pc, Elf* elf) {
-  if (!elf->valid()) {
-    return rel_pc;
-  }
-
-  if (rel_pc < 4) {
-    return rel_pc;
-  }
-  return rel_pc - 4;
-}
-
-void RegsArm64::SetFromRaw() {
-  set_pc(regs_[ARM64_REG_PC]);
-  set_sp(regs_[ARM64_REG_SP]);
-}
-
-bool RegsArm64::SetPcFromReturnAddress(Memory*) {
-  if (pc() == regs_[ARM64_REG_LR]) {
-    return false;
-  }
-
-  set_pc(regs_[ARM64_REG_LR]);
-  return true;
-}
-
-void RegsArm64::IterateRegisters(std::function<void(const char*, uint64_t)> fn) {
-  fn("x0", regs_[ARM64_REG_R0]);
-  fn("x1", regs_[ARM64_REG_R1]);
-  fn("x2", regs_[ARM64_REG_R2]);
-  fn("x3", regs_[ARM64_REG_R3]);
-  fn("x4", regs_[ARM64_REG_R4]);
-  fn("x5", regs_[ARM64_REG_R5]);
-  fn("x6", regs_[ARM64_REG_R6]);
-  fn("x7", regs_[ARM64_REG_R7]);
-  fn("x8", regs_[ARM64_REG_R8]);
-  fn("x9", regs_[ARM64_REG_R9]);
-  fn("x10", regs_[ARM64_REG_R10]);
-  fn("x11", regs_[ARM64_REG_R11]);
-  fn("x12", regs_[ARM64_REG_R12]);
-  fn("x13", regs_[ARM64_REG_R13]);
-  fn("x14", regs_[ARM64_REG_R14]);
-  fn("x15", regs_[ARM64_REG_R15]);
-  fn("x16", regs_[ARM64_REG_R16]);
-  fn("x17", regs_[ARM64_REG_R17]);
-  fn("x18", regs_[ARM64_REG_R18]);
-  fn("x19", regs_[ARM64_REG_R19]);
-  fn("x20", regs_[ARM64_REG_R20]);
-  fn("x21", regs_[ARM64_REG_R21]);
-  fn("x22", regs_[ARM64_REG_R22]);
-  fn("x23", regs_[ARM64_REG_R23]);
-  fn("x24", regs_[ARM64_REG_R24]);
-  fn("x25", regs_[ARM64_REG_R25]);
-  fn("x26", regs_[ARM64_REG_R26]);
-  fn("x27", regs_[ARM64_REG_R27]);
-  fn("x28", regs_[ARM64_REG_R28]);
-  fn("x29", regs_[ARM64_REG_R29]);
-  fn("sp", regs_[ARM64_REG_SP]);
-  fn("lr", regs_[ARM64_REG_LR]);
-  fn("pc", regs_[ARM64_REG_PC]);
-}
-
-RegsX86::RegsX86()
-    : RegsImpl<uint32_t>(X86_REG_LAST, X86_REG_SP, Location(LOCATION_SP_OFFSET, -4)) {}
-
-uint32_t RegsX86::MachineType() {
-  return EM_386;
-}
-
-uint64_t RegsX86::GetAdjustedPc(uint64_t rel_pc, Elf* elf) {
-  if (!elf->valid()) {
-    return rel_pc;
-  }
-
-  if (rel_pc == 0) {
-    return 0;
-  }
-  return rel_pc - 1;
-}
-
-void RegsX86::SetFromRaw() {
-  set_pc(regs_[X86_REG_PC]);
-  set_sp(regs_[X86_REG_SP]);
-}
-
-bool RegsX86::SetPcFromReturnAddress(Memory* process_memory) {
-  // Attempt to get the return address from the top of the stack.
-  uint32_t new_pc;
-  if (!process_memory->ReadFully(sp_, &new_pc, sizeof(new_pc)) || new_pc == pc()) {
-    return false;
-  }
-
-  set_pc(new_pc);
-  return true;
-}
-
-void RegsX86::IterateRegisters(std::function<void(const char*, uint64_t)> fn) {
-  fn("eax", regs_[X86_REG_EAX]);
-  fn("ebx", regs_[X86_REG_EBX]);
-  fn("ecx", regs_[X86_REG_ECX]);
-  fn("edx", regs_[X86_REG_EDX]);
-  fn("ebp", regs_[X86_REG_EBP]);
-  fn("edi", regs_[X86_REG_EDI]);
-  fn("esi", regs_[X86_REG_ESI]);
-  fn("esp", regs_[X86_REG_ESP]);
-  fn("eip", regs_[X86_REG_EIP]);
-}
-
-RegsX86_64::RegsX86_64()
-    : RegsImpl<uint64_t>(X86_64_REG_LAST, X86_64_REG_SP, Location(LOCATION_SP_OFFSET, -8)) {}
-
-uint32_t RegsX86_64::MachineType() {
-  return EM_X86_64;
-}
-
-uint64_t RegsX86_64::GetAdjustedPc(uint64_t rel_pc, Elf* elf) {
-  if (!elf->valid()) {
-    return rel_pc;
-  }
-
-  if (rel_pc == 0) {
-    return 0;
-  }
-
-  return rel_pc - 1;
-}
-
-void RegsX86_64::SetFromRaw() {
-  set_pc(regs_[X86_64_REG_PC]);
-  set_sp(regs_[X86_64_REG_SP]);
-}
-
-bool RegsX86_64::SetPcFromReturnAddress(Memory* process_memory) {
-  // Attempt to get the return address from the top of the stack.
-  uint64_t new_pc;
-  if (!process_memory->ReadFully(sp_, &new_pc, sizeof(new_pc)) || new_pc == pc()) {
-    return false;
-  }
-
-  set_pc(new_pc);
-  return true;
-}
-
-void RegsX86_64::IterateRegisters(std::function<void(const char*, uint64_t)> fn) {
-  fn("rax", regs_[X86_64_REG_RAX]);
-  fn("rbx", regs_[X86_64_REG_RBX]);
-  fn("rcx", regs_[X86_64_REG_RCX]);
-  fn("rdx", regs_[X86_64_REG_RDX]);
-  fn("r8", regs_[X86_64_REG_R8]);
-  fn("r9", regs_[X86_64_REG_R9]);
-  fn("r10", regs_[X86_64_REG_R10]);
-  fn("r11", regs_[X86_64_REG_R11]);
-  fn("r12", regs_[X86_64_REG_R12]);
-  fn("r13", regs_[X86_64_REG_R13]);
-  fn("r14", regs_[X86_64_REG_R14]);
-  fn("r15", regs_[X86_64_REG_R15]);
-  fn("rdi", regs_[X86_64_REG_RDI]);
-  fn("rsi", regs_[X86_64_REG_RSI]);
-  fn("rbp", regs_[X86_64_REG_RBP]);
-  fn("rsp", regs_[X86_64_REG_RSP]);
-  fn("rip", regs_[X86_64_REG_RIP]);
-}
-
-static Regs* ReadArm(void* remote_data) {
-  arm_user_regs* user = reinterpret_cast<arm_user_regs*>(remote_data);
-
-  RegsArm* regs = new RegsArm();
-  memcpy(regs->RawData(), &user->regs[0], ARM_REG_LAST * sizeof(uint32_t));
-  regs->SetFromRaw();
-  return regs;
-}
-
-static Regs* ReadArm64(void* remote_data) {
-  arm64_user_regs* user = reinterpret_cast<arm64_user_regs*>(remote_data);
-
-  RegsArm64* regs = new RegsArm64();
-  memcpy(regs->RawData(), &user->regs[0], (ARM64_REG_R31 + 1) * sizeof(uint64_t));
-  uint64_t* reg_data = reinterpret_cast<uint64_t*>(regs->RawData());
-  reg_data[ARM64_REG_PC] = user->pc;
-  reg_data[ARM64_REG_SP] = user->sp;
-  regs->SetFromRaw();
-  return regs;
-}
-
-static Regs* ReadX86(void* remote_data) {
-  x86_user_regs* user = reinterpret_cast<x86_user_regs*>(remote_data);
-
-  RegsX86* regs = new RegsX86();
-  (*regs)[X86_REG_EAX] = user->eax;
-  (*regs)[X86_REG_EBX] = user->ebx;
-  (*regs)[X86_REG_ECX] = user->ecx;
-  (*regs)[X86_REG_EDX] = user->edx;
-  (*regs)[X86_REG_EBP] = user->ebp;
-  (*regs)[X86_REG_EDI] = user->edi;
-  (*regs)[X86_REG_ESI] = user->esi;
-  (*regs)[X86_REG_ESP] = user->esp;
-  (*regs)[X86_REG_EIP] = user->eip;
-
-  regs->SetFromRaw();
-  return regs;
-}
-
-static Regs* ReadX86_64(void* remote_data) {
-  x86_64_user_regs* user = reinterpret_cast<x86_64_user_regs*>(remote_data);
-
-  RegsX86_64* regs = new RegsX86_64();
-  (*regs)[X86_64_REG_RAX] = user->rax;
-  (*regs)[X86_64_REG_RBX] = user->rbx;
-  (*regs)[X86_64_REG_RCX] = user->rcx;
-  (*regs)[X86_64_REG_RDX] = user->rdx;
-  (*regs)[X86_64_REG_R8] = user->r8;
-  (*regs)[X86_64_REG_R9] = user->r9;
-  (*regs)[X86_64_REG_R10] = user->r10;
-  (*regs)[X86_64_REG_R11] = user->r11;
-  (*regs)[X86_64_REG_R12] = user->r12;
-  (*regs)[X86_64_REG_R13] = user->r13;
-  (*regs)[X86_64_REG_R14] = user->r14;
-  (*regs)[X86_64_REG_R15] = user->r15;
-  (*regs)[X86_64_REG_RDI] = user->rdi;
-  (*regs)[X86_64_REG_RSI] = user->rsi;
-  (*regs)[X86_64_REG_RBP] = user->rbp;
-  (*regs)[X86_64_REG_RSP] = user->rsp;
-  (*regs)[X86_64_REG_RIP] = user->rip;
-
-  regs->SetFromRaw();
-  return regs;
-}
+// The largest user structure.
+constexpr size_t MAX_USER_REGS_SIZE = sizeof(arm64_user_regs) + 10;
 
 // This function assumes that reg_data is already aligned to a 64 bit value.
 // If not this could crash with an unaligned access.
@@ -348,106 +53,42 @@
 
   switch (io.iov_len) {
   case sizeof(x86_user_regs):
-    return ReadX86(buffer.data());
+    return RegsX86::Read(buffer.data());
   case sizeof(x86_64_user_regs):
-    return ReadX86_64(buffer.data());
+    return RegsX86_64::Read(buffer.data());
   case sizeof(arm_user_regs):
-    return ReadArm(buffer.data());
+    return RegsArm::Read(buffer.data());
   case sizeof(arm64_user_regs):
-    return ReadArm64(buffer.data());
+    return RegsArm64::Read(buffer.data());
   }
   return nullptr;
 }
 
-static Regs* CreateFromArmUcontext(void* ucontext) {
-  arm_ucontext_t* arm_ucontext = reinterpret_cast<arm_ucontext_t*>(ucontext);
-
-  RegsArm* regs = new RegsArm();
-  memcpy(regs->RawData(), &arm_ucontext->uc_mcontext.regs[0], ARM_REG_LAST * sizeof(uint32_t));
-  regs->SetFromRaw();
-  return regs;
-}
-
-static Regs* CreateFromArm64Ucontext(void* ucontext) {
-  arm64_ucontext_t* arm64_ucontext = reinterpret_cast<arm64_ucontext_t*>(ucontext);
-
-  RegsArm64* regs = new RegsArm64();
-  memcpy(regs->RawData(), &arm64_ucontext->uc_mcontext.regs[0], ARM64_REG_LAST * sizeof(uint64_t));
-  regs->SetFromRaw();
-  return regs;
-}
-
-void RegsX86::SetFromUcontext(x86_ucontext_t* ucontext) {
-  // Put the registers in the expected order.
-  regs_[X86_REG_EDI] = ucontext->uc_mcontext.edi;
-  regs_[X86_REG_ESI] = ucontext->uc_mcontext.esi;
-  regs_[X86_REG_EBP] = ucontext->uc_mcontext.ebp;
-  regs_[X86_REG_ESP] = ucontext->uc_mcontext.esp;
-  regs_[X86_REG_EBX] = ucontext->uc_mcontext.ebx;
-  regs_[X86_REG_EDX] = ucontext->uc_mcontext.edx;
-  regs_[X86_REG_ECX] = ucontext->uc_mcontext.ecx;
-  regs_[X86_REG_EAX] = ucontext->uc_mcontext.eax;
-  regs_[X86_REG_EIP] = ucontext->uc_mcontext.eip;
-  SetFromRaw();
-}
-
-static Regs* CreateFromX86Ucontext(void* ucontext) {
-  x86_ucontext_t* x86_ucontext = reinterpret_cast<x86_ucontext_t*>(ucontext);
-
-  RegsX86* regs = new RegsX86();
-  regs->SetFromUcontext(x86_ucontext);
-  return regs;
-}
-
-void RegsX86_64::SetFromUcontext(x86_64_ucontext_t* ucontext) {
-  // R8-R15
-  memcpy(&regs_[X86_64_REG_R8], &ucontext->uc_mcontext.r8, 8 * sizeof(uint64_t));
-
-  // Rest of the registers.
-  regs_[X86_64_REG_RDI] = ucontext->uc_mcontext.rdi;
-  regs_[X86_64_REG_RSI] = ucontext->uc_mcontext.rsi;
-  regs_[X86_64_REG_RBP] = ucontext->uc_mcontext.rbp;
-  regs_[X86_64_REG_RBX] = ucontext->uc_mcontext.rbx;
-  regs_[X86_64_REG_RDX] = ucontext->uc_mcontext.rdx;
-  regs_[X86_64_REG_RAX] = ucontext->uc_mcontext.rax;
-  regs_[X86_64_REG_RCX] = ucontext->uc_mcontext.rcx;
-  regs_[X86_64_REG_RSP] = ucontext->uc_mcontext.rsp;
-  regs_[X86_64_REG_RIP] = ucontext->uc_mcontext.rip;
-
-  SetFromRaw();
-}
-
-static Regs* CreateFromX86_64Ucontext(void* ucontext) {
-  x86_64_ucontext_t* x86_64_ucontext = reinterpret_cast<x86_64_ucontext_t*>(ucontext);
-
-  RegsX86_64* regs = new RegsX86_64();
-  regs->SetFromUcontext(x86_64_ucontext);
-  return regs;
-}
-
-Regs* Regs::CreateFromUcontext(uint32_t machine_type, void* ucontext) {
-  switch (machine_type) {
-    case EM_386:
-      return CreateFromX86Ucontext(ucontext);
-    case EM_X86_64:
-      return CreateFromX86_64Ucontext(ucontext);
-    case EM_ARM:
-      return CreateFromArmUcontext(ucontext);
-    case EM_AARCH64:
-      return CreateFromArm64Ucontext(ucontext);
+Regs* Regs::CreateFromUcontext(ArchEnum arch, void* ucontext) {
+  switch (arch) {
+    case ARCH_X86:
+      return RegsX86::CreateFromUcontext(ucontext);
+    case ARCH_X86_64:
+      return RegsX86_64::CreateFromUcontext(ucontext);
+    case ARCH_ARM:
+      return RegsArm::CreateFromUcontext(ucontext);
+    case ARCH_ARM64:
+      return RegsArm64::CreateFromUcontext(ucontext);
+    case ARCH_UNKNOWN:
+    default:
+      return nullptr;
   }
-  return nullptr;
 }
 
-uint32_t Regs::CurrentMachineType() {
+ArchEnum Regs::CurrentArch() {
 #if defined(__arm__)
-  return EM_ARM;
+  return ARCH_ARM;
 #elif defined(__aarch64__)
-  return EM_AARCH64;
+  return ARCH_ARM64;
 #elif defined(__i386__)
-  return EM_386;
+  return ARCH_X86;
 #elif defined(__x86_64__)
-  return EM_X86_64;
+  return ARCH_X86_64;
 #else
   abort();
 #endif
@@ -469,192 +110,4 @@
   return regs;
 }
 
-bool RegsArm::StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) {
-  uint32_t data;
-  Memory* elf_memory = elf->memory();
-  // Read from elf memory since it is usually more expensive to read from
-  // process memory.
-  if (!elf_memory->ReadFully(rel_pc, &data, sizeof(data))) {
-    return false;
-  }
-
-  uint64_t offset = 0;
-  if (data == 0xe3a07077 || data == 0xef900077 || data == 0xdf002777) {
-    // non-RT sigreturn call.
-    // __restore:
-    //
-    // Form 1 (arm):
-    // 0x77 0x70              mov r7, #0x77
-    // 0xa0 0xe3              svc 0x00000000
-    //
-    // Form 2 (arm):
-    // 0x77 0x00 0x90 0xef    svc 0x00900077
-    //
-    // Form 3 (thumb):
-    // 0x77 0x27              movs r7, #77
-    // 0x00 0xdf              svc 0
-    if (!process_memory->ReadFully(sp(), &data, sizeof(data))) {
-      return false;
-    }
-    if (data == 0x5ac3c35a) {
-      // SP + uc_mcontext offset + r0 offset.
-      offset = sp() + 0x14 + 0xc;
-    } else {
-      // SP + r0 offset
-      offset = sp() + 0xc;
-    }
-  } else if (data == 0xe3a070ad || data == 0xef9000ad || data == 0xdf0027ad) {
-    // RT sigreturn call.
-    // __restore_rt:
-    //
-    // Form 1 (arm):
-    // 0xad 0x70      mov r7, #0xad
-    // 0xa0 0xe3      svc 0x00000000
-    //
-    // Form 2 (arm):
-    // 0xad 0x00 0x90 0xef    svc 0x009000ad
-    //
-    // Form 3 (thumb):
-    // 0xad 0x27              movs r7, #ad
-    // 0x00 0xdf              svc 0
-    if (!process_memory->ReadFully(sp(), &data, sizeof(data))) {
-      return false;
-    }
-    if (data == sp() + 8) {
-      // SP + 8 + sizeof(siginfo_t) + uc_mcontext_offset + r0 offset
-      offset = sp() + 8 + 0x80 + 0x14 + 0xc;
-    } else {
-      // SP + sizeof(siginfo_t) + uc_mcontext_offset + r0 offset
-      offset = sp() + 0x80 + 0x14 + 0xc;
-    }
-  }
-  if (offset == 0) {
-    return false;
-  }
-
-  if (!process_memory->ReadFully(offset, regs_.data(), sizeof(uint32_t) * ARM_REG_LAST)) {
-    return false;
-  }
-  SetFromRaw();
-  return true;
-}
-
-bool RegsArm64::StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) {
-  uint64_t data;
-  Memory* elf_memory = elf->memory();
-  // Read from elf memory since it is usually more expensive to read from
-  // process memory.
-  if (!elf_memory->ReadFully(rel_pc, &data, sizeof(data))) {
-    return false;
-  }
-
-  // Look for the kernel sigreturn function.
-  // __kernel_rt_sigreturn:
-  // 0xd2801168     mov x8, #0x8b
-  // 0xd4000001     svc #0x0
-  if (data != 0xd4000001d2801168ULL) {
-    return false;
-  }
-
-  // SP + sizeof(siginfo_t) + uc_mcontext offset + X0 offset.
-  if (!process_memory->ReadFully(sp() + 0x80 + 0xb0 + 0x08, regs_.data(),
-                                 sizeof(uint64_t) * ARM64_REG_LAST)) {
-    return false;
-  }
-
-  SetFromRaw();
-  return true;
-}
-
-bool RegsX86::StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) {
-  uint64_t data;
-  Memory* elf_memory = elf->memory();
-  // Read from elf memory since it is usually more expensive to read from
-  // process memory.
-  if (!elf_memory->ReadFully(rel_pc, &data, sizeof(data))) {
-    return false;
-  }
-
-  if (data == 0x80cd00000077b858ULL) {
-    // Without SA_SIGINFO set, the return sequence is:
-    //
-    //   __restore:
-    //   0x58                            pop %eax
-    //   0xb8 0x77 0x00 0x00 0x00        movl 0x77,%eax
-    //   0xcd 0x80                       int 0x80
-    //
-    // SP points at arguments:
-    //   int signum
-    //   struct sigcontext (same format as mcontext)
-    struct x86_mcontext_t context;
-    if (!process_memory->ReadFully(sp() + 4, &context, sizeof(context))) {
-      return false;
-    }
-    regs_[X86_REG_EBP] = context.ebp;
-    regs_[X86_REG_ESP] = context.esp;
-    regs_[X86_REG_EBX] = context.ebx;
-    regs_[X86_REG_EDX] = context.edx;
-    regs_[X86_REG_ECX] = context.ecx;
-    regs_[X86_REG_EAX] = context.eax;
-    regs_[X86_REG_EIP] = context.eip;
-    SetFromRaw();
-    return true;
-  } else if ((data & 0x00ffffffffffffffULL) == 0x0080cd000000adb8ULL) {
-    // With SA_SIGINFO set, the return sequence is:
-    //
-    //   __restore_rt:
-    //   0xb8 0xad 0x00 0x00 0x00        movl 0xad,%eax
-    //   0xcd 0x80                       int 0x80
-    //
-    // SP points at arguments:
-    //   int signum
-    //   siginfo*
-    //   ucontext*
-
-    // Get the location of the sigcontext data.
-    uint32_t ptr;
-    if (!process_memory->ReadFully(sp() + 8, &ptr, sizeof(ptr))) {
-      return false;
-    }
-    // Only read the portion of the data structure we care about.
-    x86_ucontext_t x86_ucontext;
-    if (!process_memory->ReadFully(ptr + 0x14, &x86_ucontext.uc_mcontext, sizeof(x86_mcontext_t))) {
-      return false;
-    }
-    SetFromUcontext(&x86_ucontext);
-    return true;
-  }
-  return false;
-}
-
-bool RegsX86_64::StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) {
-  uint64_t data;
-  Memory* elf_memory = elf->memory();
-  // Read from elf memory since it is usually more expensive to read from
-  // process memory.
-  if (!elf_memory->ReadFully(rel_pc, &data, sizeof(data)) || data != 0x0f0000000fc0c748) {
-    return false;
-  }
-
-  uint16_t data2;
-  if (!elf_memory->ReadFully(rel_pc + 8, &data2, sizeof(data2)) || data2 != 0x0f05) {
-    return false;
-  }
-
-  // __restore_rt:
-  // 0x48 0xc7 0xc0 0x0f 0x00 0x00 0x00   mov $0xf,%rax
-  // 0x0f 0x05                            syscall
-  // 0x0f                                 nopl 0x0($rax)
-
-  // Read the mcontext data from the stack.
-  // sp points to the ucontext data structure, read only the mcontext part.
-  x86_64_ucontext_t x86_64_ucontext;
-  if (!process_memory->ReadFully(sp() + 0x28, &x86_64_ucontext.uc_mcontext,
-                                 sizeof(x86_64_mcontext_t))) {
-    return false;
-  }
-  SetFromUcontext(&x86_64_ucontext);
-  return true;
-}
-
 }  // namespace unwindstack
diff --git a/libunwindstack/RegsArm.cpp b/libunwindstack/RegsArm.cpp
new file mode 100644
index 0000000..34f29bd
--- /dev/null
+++ b/libunwindstack/RegsArm.cpp
@@ -0,0 +1,186 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdint.h>
+
+#include <functional>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/MapInfo.h>
+#include <unwindstack/Memory.h>
+#include <unwindstack/RegsArm.h>
+
+#include "MachineArm.h"
+#include "UcontextArm.h"
+#include "UserArm.h"
+
+namespace unwindstack {
+
+RegsArm::RegsArm()
+    : RegsImpl<uint32_t>(ARM_REG_LAST, ARM_REG_SP, Location(LOCATION_REGISTER, ARM_REG_LR)) {}
+
+ArchEnum RegsArm::Arch() {
+  return ARCH_ARM;
+}
+
+uint64_t RegsArm::GetAdjustedPc(uint64_t rel_pc, Elf* elf) {
+  if (!elf->valid()) {
+    return rel_pc;
+  }
+
+  uint64_t load_bias = elf->GetLoadBias();
+  if (rel_pc < load_bias) {
+    return rel_pc;
+  }
+  uint64_t adjusted_rel_pc = rel_pc - load_bias;
+
+  if (adjusted_rel_pc < 5) {
+    return rel_pc;
+  }
+
+  if (adjusted_rel_pc & 1) {
+    // This is a thumb instruction, it could be 2 or 4 bytes.
+    uint32_t value;
+    if (rel_pc < 5 || !elf->memory()->ReadFully(adjusted_rel_pc - 5, &value, sizeof(value)) ||
+        (value & 0xe000f000) != 0xe000f000) {
+      return rel_pc - 2;
+    }
+  }
+  return rel_pc - 4;
+}
+
+void RegsArm::SetFromRaw() {
+  set_pc(regs_[ARM_REG_PC]);
+  set_sp(regs_[ARM_REG_SP]);
+}
+
+bool RegsArm::SetPcFromReturnAddress(Memory*) {
+  if (pc() == regs_[ARM_REG_LR]) {
+    return false;
+  }
+
+  set_pc(regs_[ARM_REG_LR]);
+  return true;
+}
+
+void RegsArm::IterateRegisters(std::function<void(const char*, uint64_t)> fn) {
+  fn("r0", regs_[ARM_REG_R0]);
+  fn("r1", regs_[ARM_REG_R1]);
+  fn("r2", regs_[ARM_REG_R2]);
+  fn("r3", regs_[ARM_REG_R3]);
+  fn("r4", regs_[ARM_REG_R4]);
+  fn("r5", regs_[ARM_REG_R5]);
+  fn("r6", regs_[ARM_REG_R6]);
+  fn("r7", regs_[ARM_REG_R7]);
+  fn("r8", regs_[ARM_REG_R8]);
+  fn("r9", regs_[ARM_REG_R9]);
+  fn("r10", regs_[ARM_REG_R10]);
+  fn("r11", regs_[ARM_REG_R11]);
+  fn("ip", regs_[ARM_REG_R12]);
+  fn("sp", regs_[ARM_REG_SP]);
+  fn("lr", regs_[ARM_REG_LR]);
+  fn("pc", regs_[ARM_REG_PC]);
+}
+
+Regs* RegsArm::Read(void* remote_data) {
+  arm_user_regs* user = reinterpret_cast<arm_user_regs*>(remote_data);
+
+  RegsArm* regs = new RegsArm();
+  memcpy(regs->RawData(), &user->regs[0], ARM_REG_LAST * sizeof(uint32_t));
+  regs->SetFromRaw();
+  return regs;
+}
+
+Regs* RegsArm::CreateFromUcontext(void* ucontext) {
+  arm_ucontext_t* arm_ucontext = reinterpret_cast<arm_ucontext_t*>(ucontext);
+
+  RegsArm* regs = new RegsArm();
+  memcpy(regs->RawData(), &arm_ucontext->uc_mcontext.regs[0], ARM_REG_LAST * sizeof(uint32_t));
+  regs->SetFromRaw();
+  return regs;
+}
+
+bool RegsArm::StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) {
+  uint32_t data;
+  Memory* elf_memory = elf->memory();
+  // Read from elf memory since it is usually more expensive to read from
+  // process memory.
+  if (!elf_memory->ReadFully(rel_pc, &data, sizeof(data))) {
+    return false;
+  }
+
+  uint64_t offset = 0;
+  if (data == 0xe3a07077 || data == 0xef900077 || data == 0xdf002777) {
+    // non-RT sigreturn call.
+    // __restore:
+    //
+    // Form 1 (arm):
+    // 0x77 0x70              mov r7, #0x77
+    // 0xa0 0xe3              svc 0x00000000
+    //
+    // Form 2 (arm):
+    // 0x77 0x00 0x90 0xef    svc 0x00900077
+    //
+    // Form 3 (thumb):
+    // 0x77 0x27              movs r7, #77
+    // 0x00 0xdf              svc 0
+    if (!process_memory->ReadFully(sp(), &data, sizeof(data))) {
+      return false;
+    }
+    if (data == 0x5ac3c35a) {
+      // SP + uc_mcontext offset + r0 offset.
+      offset = sp() + 0x14 + 0xc;
+    } else {
+      // SP + r0 offset
+      offset = sp() + 0xc;
+    }
+  } else if (data == 0xe3a070ad || data == 0xef9000ad || data == 0xdf0027ad) {
+    // RT sigreturn call.
+    // __restore_rt:
+    //
+    // Form 1 (arm):
+    // 0xad 0x70      mov r7, #0xad
+    // 0xa0 0xe3      svc 0x00000000
+    //
+    // Form 2 (arm):
+    // 0xad 0x00 0x90 0xef    svc 0x009000ad
+    //
+    // Form 3 (thumb):
+    // 0xad 0x27              movs r7, #ad
+    // 0x00 0xdf              svc 0
+    if (!process_memory->ReadFully(sp(), &data, sizeof(data))) {
+      return false;
+    }
+    if (data == sp() + 8) {
+      // SP + 8 + sizeof(siginfo_t) + uc_mcontext_offset + r0 offset
+      offset = sp() + 8 + 0x80 + 0x14 + 0xc;
+    } else {
+      // SP + sizeof(siginfo_t) + uc_mcontext_offset + r0 offset
+      offset = sp() + 0x80 + 0x14 + 0xc;
+    }
+  }
+  if (offset == 0) {
+    return false;
+  }
+
+  if (!process_memory->ReadFully(offset, regs_.data(), sizeof(uint32_t) * ARM_REG_LAST)) {
+    return false;
+  }
+  SetFromRaw();
+  return true;
+}
+
+}  // namespace unwindstack
diff --git a/libunwindstack/RegsArm64.cpp b/libunwindstack/RegsArm64.cpp
new file mode 100644
index 0000000..2077bc5
--- /dev/null
+++ b/libunwindstack/RegsArm64.cpp
@@ -0,0 +1,148 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdint.h>
+
+#include <functional>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/MapInfo.h>
+#include <unwindstack/Memory.h>
+#include <unwindstack/RegsArm64.h>
+
+#include "MachineArm64.h"
+#include "UcontextArm64.h"
+#include "UserArm64.h"
+
+namespace unwindstack {
+
+RegsArm64::RegsArm64()
+    : RegsImpl<uint64_t>(ARM64_REG_LAST, ARM64_REG_SP, Location(LOCATION_REGISTER, ARM64_REG_LR)) {}
+
+ArchEnum RegsArm64::Arch() {
+  return ARCH_ARM64;
+}
+
+uint64_t RegsArm64::GetAdjustedPc(uint64_t rel_pc, Elf* elf) {
+  if (!elf->valid()) {
+    return rel_pc;
+  }
+
+  if (rel_pc < 4) {
+    return rel_pc;
+  }
+  return rel_pc - 4;
+}
+
+void RegsArm64::SetFromRaw() {
+  set_pc(regs_[ARM64_REG_PC]);
+  set_sp(regs_[ARM64_REG_SP]);
+}
+
+bool RegsArm64::SetPcFromReturnAddress(Memory*) {
+  if (pc() == regs_[ARM64_REG_LR]) {
+    return false;
+  }
+
+  set_pc(regs_[ARM64_REG_LR]);
+  return true;
+}
+
+void RegsArm64::IterateRegisters(std::function<void(const char*, uint64_t)> fn) {
+  fn("x0", regs_[ARM64_REG_R0]);
+  fn("x1", regs_[ARM64_REG_R1]);
+  fn("x2", regs_[ARM64_REG_R2]);
+  fn("x3", regs_[ARM64_REG_R3]);
+  fn("x4", regs_[ARM64_REG_R4]);
+  fn("x5", regs_[ARM64_REG_R5]);
+  fn("x6", regs_[ARM64_REG_R6]);
+  fn("x7", regs_[ARM64_REG_R7]);
+  fn("x8", regs_[ARM64_REG_R8]);
+  fn("x9", regs_[ARM64_REG_R9]);
+  fn("x10", regs_[ARM64_REG_R10]);
+  fn("x11", regs_[ARM64_REG_R11]);
+  fn("x12", regs_[ARM64_REG_R12]);
+  fn("x13", regs_[ARM64_REG_R13]);
+  fn("x14", regs_[ARM64_REG_R14]);
+  fn("x15", regs_[ARM64_REG_R15]);
+  fn("x16", regs_[ARM64_REG_R16]);
+  fn("x17", regs_[ARM64_REG_R17]);
+  fn("x18", regs_[ARM64_REG_R18]);
+  fn("x19", regs_[ARM64_REG_R19]);
+  fn("x20", regs_[ARM64_REG_R20]);
+  fn("x21", regs_[ARM64_REG_R21]);
+  fn("x22", regs_[ARM64_REG_R22]);
+  fn("x23", regs_[ARM64_REG_R23]);
+  fn("x24", regs_[ARM64_REG_R24]);
+  fn("x25", regs_[ARM64_REG_R25]);
+  fn("x26", regs_[ARM64_REG_R26]);
+  fn("x27", regs_[ARM64_REG_R27]);
+  fn("x28", regs_[ARM64_REG_R28]);
+  fn("x29", regs_[ARM64_REG_R29]);
+  fn("sp", regs_[ARM64_REG_SP]);
+  fn("lr", regs_[ARM64_REG_LR]);
+  fn("pc", regs_[ARM64_REG_PC]);
+}
+
+Regs* RegsArm64::Read(void* remote_data) {
+  arm64_user_regs* user = reinterpret_cast<arm64_user_regs*>(remote_data);
+
+  RegsArm64* regs = new RegsArm64();
+  memcpy(regs->RawData(), &user->regs[0], (ARM64_REG_R31 + 1) * sizeof(uint64_t));
+  uint64_t* reg_data = reinterpret_cast<uint64_t*>(regs->RawData());
+  reg_data[ARM64_REG_PC] = user->pc;
+  reg_data[ARM64_REG_SP] = user->sp;
+  regs->SetFromRaw();
+  return regs;
+}
+
+Regs* RegsArm64::CreateFromUcontext(void* ucontext) {
+  arm64_ucontext_t* arm64_ucontext = reinterpret_cast<arm64_ucontext_t*>(ucontext);
+
+  RegsArm64* regs = new RegsArm64();
+  memcpy(regs->RawData(), &arm64_ucontext->uc_mcontext.regs[0], ARM64_REG_LAST * sizeof(uint64_t));
+  regs->SetFromRaw();
+  return regs;
+}
+
+bool RegsArm64::StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) {
+  uint64_t data;
+  Memory* elf_memory = elf->memory();
+  // Read from elf memory since it is usually more expensive to read from
+  // process memory.
+  if (!elf_memory->ReadFully(rel_pc, &data, sizeof(data))) {
+    return false;
+  }
+
+  // Look for the kernel sigreturn function.
+  // __kernel_rt_sigreturn:
+  // 0xd2801168     mov x8, #0x8b
+  // 0xd4000001     svc #0x0
+  if (data != 0xd4000001d2801168ULL) {
+    return false;
+  }
+
+  // SP + sizeof(siginfo_t) + uc_mcontext offset + X0 offset.
+  if (!process_memory->ReadFully(sp() + 0x80 + 0xb0 + 0x08, regs_.data(),
+                                 sizeof(uint64_t) * ARM64_REG_LAST)) {
+    return false;
+  }
+
+  SetFromRaw();
+  return true;
+}
+
+}  // namespace unwindstack
diff --git a/libunwindstack/RegsX86.cpp b/libunwindstack/RegsX86.cpp
new file mode 100644
index 0000000..ef2f3de
--- /dev/null
+++ b/libunwindstack/RegsX86.cpp
@@ -0,0 +1,179 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdint.h>
+
+#include <functional>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/MapInfo.h>
+#include <unwindstack/Memory.h>
+#include <unwindstack/RegsX86.h>
+
+#include "MachineX86.h"
+#include "UcontextX86.h"
+#include "UserX86.h"
+
+namespace unwindstack {
+
+RegsX86::RegsX86()
+    : RegsImpl<uint32_t>(X86_REG_LAST, X86_REG_SP, Location(LOCATION_SP_OFFSET, -4)) {}
+
+ArchEnum RegsX86::Arch() {
+  return ARCH_X86;
+}
+
+uint64_t RegsX86::GetAdjustedPc(uint64_t rel_pc, Elf* elf) {
+  if (!elf->valid()) {
+    return rel_pc;
+  }
+
+  if (rel_pc == 0) {
+    return 0;
+  }
+  return rel_pc - 1;
+}
+
+void RegsX86::SetFromRaw() {
+  set_pc(regs_[X86_REG_PC]);
+  set_sp(regs_[X86_REG_SP]);
+}
+
+bool RegsX86::SetPcFromReturnAddress(Memory* process_memory) {
+  // Attempt to get the return address from the top of the stack.
+  uint32_t new_pc;
+  if (!process_memory->ReadFully(sp_, &new_pc, sizeof(new_pc)) || new_pc == pc()) {
+    return false;
+  }
+
+  set_pc(new_pc);
+  return true;
+}
+
+void RegsX86::IterateRegisters(std::function<void(const char*, uint64_t)> fn) {
+  fn("eax", regs_[X86_REG_EAX]);
+  fn("ebx", regs_[X86_REG_EBX]);
+  fn("ecx", regs_[X86_REG_ECX]);
+  fn("edx", regs_[X86_REG_EDX]);
+  fn("ebp", regs_[X86_REG_EBP]);
+  fn("edi", regs_[X86_REG_EDI]);
+  fn("esi", regs_[X86_REG_ESI]);
+  fn("esp", regs_[X86_REG_ESP]);
+  fn("eip", regs_[X86_REG_EIP]);
+}
+
+Regs* RegsX86::Read(void* user_data) {
+  x86_user_regs* user = reinterpret_cast<x86_user_regs*>(user_data);
+
+  RegsX86* regs = new RegsX86();
+  (*regs)[X86_REG_EAX] = user->eax;
+  (*regs)[X86_REG_EBX] = user->ebx;
+  (*regs)[X86_REG_ECX] = user->ecx;
+  (*regs)[X86_REG_EDX] = user->edx;
+  (*regs)[X86_REG_EBP] = user->ebp;
+  (*regs)[X86_REG_EDI] = user->edi;
+  (*regs)[X86_REG_ESI] = user->esi;
+  (*regs)[X86_REG_ESP] = user->esp;
+  (*regs)[X86_REG_EIP] = user->eip;
+
+  regs->SetFromRaw();
+  return regs;
+}
+
+void RegsX86::SetFromUcontext(x86_ucontext_t* ucontext) {
+  // Put the registers in the expected order.
+  regs_[X86_REG_EDI] = ucontext->uc_mcontext.edi;
+  regs_[X86_REG_ESI] = ucontext->uc_mcontext.esi;
+  regs_[X86_REG_EBP] = ucontext->uc_mcontext.ebp;
+  regs_[X86_REG_ESP] = ucontext->uc_mcontext.esp;
+  regs_[X86_REG_EBX] = ucontext->uc_mcontext.ebx;
+  regs_[X86_REG_EDX] = ucontext->uc_mcontext.edx;
+  regs_[X86_REG_ECX] = ucontext->uc_mcontext.ecx;
+  regs_[X86_REG_EAX] = ucontext->uc_mcontext.eax;
+  regs_[X86_REG_EIP] = ucontext->uc_mcontext.eip;
+  SetFromRaw();
+}
+
+Regs* RegsX86::CreateFromUcontext(void* ucontext) {
+  x86_ucontext_t* x86_ucontext = reinterpret_cast<x86_ucontext_t*>(ucontext);
+
+  RegsX86* regs = new RegsX86();
+  regs->SetFromUcontext(x86_ucontext);
+  return regs;
+}
+
+bool RegsX86::StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) {
+  uint64_t data;
+  Memory* elf_memory = elf->memory();
+  // Read from elf memory since it is usually more expensive to read from
+  // process memory.
+  if (!elf_memory->ReadFully(rel_pc, &data, sizeof(data))) {
+    return false;
+  }
+
+  if (data == 0x80cd00000077b858ULL) {
+    // Without SA_SIGINFO set, the return sequence is:
+    //
+    //   __restore:
+    //   0x58                            pop %eax
+    //   0xb8 0x77 0x00 0x00 0x00        movl 0x77,%eax
+    //   0xcd 0x80                       int 0x80
+    //
+    // SP points at arguments:
+    //   int signum
+    //   struct sigcontext (same format as mcontext)
+    struct x86_mcontext_t context;
+    if (!process_memory->ReadFully(sp() + 4, &context, sizeof(context))) {
+      return false;
+    }
+    regs_[X86_REG_EBP] = context.ebp;
+    regs_[X86_REG_ESP] = context.esp;
+    regs_[X86_REG_EBX] = context.ebx;
+    regs_[X86_REG_EDX] = context.edx;
+    regs_[X86_REG_ECX] = context.ecx;
+    regs_[X86_REG_EAX] = context.eax;
+    regs_[X86_REG_EIP] = context.eip;
+    SetFromRaw();
+    return true;
+  } else if ((data & 0x00ffffffffffffffULL) == 0x0080cd000000adb8ULL) {
+    // With SA_SIGINFO set, the return sequence is:
+    //
+    //   __restore_rt:
+    //   0xb8 0xad 0x00 0x00 0x00        movl 0xad,%eax
+    //   0xcd 0x80                       int 0x80
+    //
+    // SP points at arguments:
+    //   int signum
+    //   siginfo*
+    //   ucontext*
+
+    // Get the location of the sigcontext data.
+    uint32_t ptr;
+    if (!process_memory->ReadFully(sp() + 8, &ptr, sizeof(ptr))) {
+      return false;
+    }
+    // Only read the portion of the data structure we care about.
+    x86_ucontext_t x86_ucontext;
+    if (!process_memory->ReadFully(ptr + 0x14, &x86_ucontext.uc_mcontext, sizeof(x86_mcontext_t))) {
+      return false;
+    }
+    SetFromUcontext(&x86_ucontext);
+    return true;
+  }
+  return false;
+}
+
+}  // namespace unwindstack
diff --git a/libunwindstack/RegsX86_64.cpp b/libunwindstack/RegsX86_64.cpp
new file mode 100644
index 0000000..70921f8
--- /dev/null
+++ b/libunwindstack/RegsX86_64.cpp
@@ -0,0 +1,169 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdint.h>
+
+#include <functional>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/MapInfo.h>
+#include <unwindstack/Memory.h>
+#include <unwindstack/RegsX86_64.h>
+
+#include "MachineX86_64.h"
+#include "UcontextX86_64.h"
+#include "UserX86_64.h"
+
+namespace unwindstack {
+
+RegsX86_64::RegsX86_64()
+    : RegsImpl<uint64_t>(X86_64_REG_LAST, X86_64_REG_SP, Location(LOCATION_SP_OFFSET, -8)) {}
+
+ArchEnum RegsX86_64::Arch() {
+  return ARCH_X86_64;
+}
+
+uint64_t RegsX86_64::GetAdjustedPc(uint64_t rel_pc, Elf* elf) {
+  if (!elf->valid()) {
+    return rel_pc;
+  }
+
+  if (rel_pc == 0) {
+    return 0;
+  }
+
+  return rel_pc - 1;
+}
+
+void RegsX86_64::SetFromRaw() {
+  set_pc(regs_[X86_64_REG_PC]);
+  set_sp(regs_[X86_64_REG_SP]);
+}
+
+bool RegsX86_64::SetPcFromReturnAddress(Memory* process_memory) {
+  // Attempt to get the return address from the top of the stack.
+  uint64_t new_pc;
+  if (!process_memory->ReadFully(sp_, &new_pc, sizeof(new_pc)) || new_pc == pc()) {
+    return false;
+  }
+
+  set_pc(new_pc);
+  return true;
+}
+
+void RegsX86_64::IterateRegisters(std::function<void(const char*, uint64_t)> fn) {
+  fn("rax", regs_[X86_64_REG_RAX]);
+  fn("rbx", regs_[X86_64_REG_RBX]);
+  fn("rcx", regs_[X86_64_REG_RCX]);
+  fn("rdx", regs_[X86_64_REG_RDX]);
+  fn("r8", regs_[X86_64_REG_R8]);
+  fn("r9", regs_[X86_64_REG_R9]);
+  fn("r10", regs_[X86_64_REG_R10]);
+  fn("r11", regs_[X86_64_REG_R11]);
+  fn("r12", regs_[X86_64_REG_R12]);
+  fn("r13", regs_[X86_64_REG_R13]);
+  fn("r14", regs_[X86_64_REG_R14]);
+  fn("r15", regs_[X86_64_REG_R15]);
+  fn("rdi", regs_[X86_64_REG_RDI]);
+  fn("rsi", regs_[X86_64_REG_RSI]);
+  fn("rbp", regs_[X86_64_REG_RBP]);
+  fn("rsp", regs_[X86_64_REG_RSP]);
+  fn("rip", regs_[X86_64_REG_RIP]);
+}
+
+Regs* RegsX86_64::Read(void* remote_data) {
+  x86_64_user_regs* user = reinterpret_cast<x86_64_user_regs*>(remote_data);
+
+  RegsX86_64* regs = new RegsX86_64();
+  (*regs)[X86_64_REG_RAX] = user->rax;
+  (*regs)[X86_64_REG_RBX] = user->rbx;
+  (*regs)[X86_64_REG_RCX] = user->rcx;
+  (*regs)[X86_64_REG_RDX] = user->rdx;
+  (*regs)[X86_64_REG_R8] = user->r8;
+  (*regs)[X86_64_REG_R9] = user->r9;
+  (*regs)[X86_64_REG_R10] = user->r10;
+  (*regs)[X86_64_REG_R11] = user->r11;
+  (*regs)[X86_64_REG_R12] = user->r12;
+  (*regs)[X86_64_REG_R13] = user->r13;
+  (*regs)[X86_64_REG_R14] = user->r14;
+  (*regs)[X86_64_REG_R15] = user->r15;
+  (*regs)[X86_64_REG_RDI] = user->rdi;
+  (*regs)[X86_64_REG_RSI] = user->rsi;
+  (*regs)[X86_64_REG_RBP] = user->rbp;
+  (*regs)[X86_64_REG_RSP] = user->rsp;
+  (*regs)[X86_64_REG_RIP] = user->rip;
+
+  regs->SetFromRaw();
+  return regs;
+}
+
+void RegsX86_64::SetFromUcontext(x86_64_ucontext_t* ucontext) {
+  // R8-R15
+  memcpy(&regs_[X86_64_REG_R8], &ucontext->uc_mcontext.r8, 8 * sizeof(uint64_t));
+
+  // Rest of the registers.
+  regs_[X86_64_REG_RDI] = ucontext->uc_mcontext.rdi;
+  regs_[X86_64_REG_RSI] = ucontext->uc_mcontext.rsi;
+  regs_[X86_64_REG_RBP] = ucontext->uc_mcontext.rbp;
+  regs_[X86_64_REG_RBX] = ucontext->uc_mcontext.rbx;
+  regs_[X86_64_REG_RDX] = ucontext->uc_mcontext.rdx;
+  regs_[X86_64_REG_RAX] = ucontext->uc_mcontext.rax;
+  regs_[X86_64_REG_RCX] = ucontext->uc_mcontext.rcx;
+  regs_[X86_64_REG_RSP] = ucontext->uc_mcontext.rsp;
+  regs_[X86_64_REG_RIP] = ucontext->uc_mcontext.rip;
+
+  SetFromRaw();
+}
+
+Regs* RegsX86_64::CreateFromUcontext(void* ucontext) {
+  x86_64_ucontext_t* x86_64_ucontext = reinterpret_cast<x86_64_ucontext_t*>(ucontext);
+
+  RegsX86_64* regs = new RegsX86_64();
+  regs->SetFromUcontext(x86_64_ucontext);
+  return regs;
+}
+
+bool RegsX86_64::StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) {
+  uint64_t data;
+  Memory* elf_memory = elf->memory();
+  // Read from elf memory since it is usually more expensive to read from
+  // process memory.
+  if (!elf_memory->ReadFully(rel_pc, &data, sizeof(data)) || data != 0x0f0000000fc0c748) {
+    return false;
+  }
+
+  uint16_t data2;
+  if (!elf_memory->ReadFully(rel_pc + 8, &data2, sizeof(data2)) || data2 != 0x0f05) {
+    return false;
+  }
+
+  // __restore_rt:
+  // 0x48 0xc7 0xc0 0x0f 0x00 0x00 0x00   mov $0xf,%rax
+  // 0x0f 0x05                            syscall
+  // 0x0f                                 nopl 0x0($rax)
+
+  // Read the mcontext data from the stack.
+  // sp points to the ucontext data structure, read only the mcontext part.
+  x86_64_ucontext_t x86_64_ucontext;
+  if (!process_memory->ReadFully(sp() + 0x28, &x86_64_ucontext.uc_mcontext,
+                                 sizeof(x86_64_mcontext_t))) {
+    return false;
+  }
+  SetFromUcontext(&x86_64_ucontext);
+  return true;
+}
+
+}  // namespace unwindstack
diff --git a/libunwindstack/Ucontext.h b/libunwindstack/Ucontext.h
deleted file mode 100644
index 22f6a89..0000000
--- a/libunwindstack/Ucontext.h
+++ /dev/null
@@ -1,184 +0,0 @@
-/*
- * Copyright (C) 2016 The Android Open Source Project
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *  * Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- *  * Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in
- *    the documentation and/or other materials provided with the
- *    distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
- * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
- * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
- * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
- * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#ifndef _LIBUNWINDSTACK_UCONTEXT_H
-#define _LIBUNWINDSTACK_UCONTEXT_H
-
-#include <stdint.h>
-
-namespace unwindstack {
-
-//-------------------------------------------------------------------
-// ARM ucontext structures
-//-------------------------------------------------------------------
-struct arm_stack_t {
-  uint32_t ss_sp;    // void __user*
-  int32_t ss_flags;  // int
-  uint32_t ss_size;  // size_t
-};
-
-struct arm_mcontext_t {
-  uint32_t trap_no;             // unsigned long
-  uint32_t error_code;          // unsigned long
-  uint32_t oldmask;             // unsigned long
-  uint32_t regs[ARM_REG_LAST];  // unsigned long
-  uint32_t cpsr;                // unsigned long
-  uint32_t fault_address;       // unsigned long
-};
-
-struct arm_ucontext_t {
-  uint32_t uc_flags;  // unsigned long
-  uint32_t uc_link;   // struct ucontext*
-  arm_stack_t uc_stack;
-  arm_mcontext_t uc_mcontext;
-  // Nothing else is used, so don't define it.
-};
-//-------------------------------------------------------------------
-
-//-------------------------------------------------------------------
-// ARM64 ucontext structures
-//-------------------------------------------------------------------
-struct arm64_stack_t {
-  uint64_t ss_sp;    // void __user*
-  int32_t ss_flags;  // int
-  uint64_t ss_size;  // size_t
-};
-
-struct arm64_sigset_t {
-  uint64_t sig;  // unsigned long
-};
-
-struct arm64_mcontext_t {
-  uint64_t fault_address;         // __u64
-  uint64_t regs[ARM64_REG_LAST];  // __u64
-  uint64_t pstate;                // __u64
-  // Nothing else is used, so don't define it.
-};
-
-struct arm64_ucontext_t {
-  uint64_t uc_flags;  // unsigned long
-  uint64_t uc_link;   // struct ucontext*
-  arm64_stack_t uc_stack;
-  arm64_sigset_t uc_sigmask;
-  // The kernel adds extra padding after uc_sigmask to match glibc sigset_t on ARM64.
-  char __padding[128 - sizeof(arm64_sigset_t)];
-  // The full structure requires 16 byte alignment, but our partial structure
-  // doesn't, so force the alignment.
-  arm64_mcontext_t uc_mcontext __attribute__((aligned(16)));
-};
-//-------------------------------------------------------------------
-
-//-------------------------------------------------------------------
-// X86 ucontext structures
-//-------------------------------------------------------------------
-struct x86_stack_t {
-  uint32_t ss_sp;    // void __user*
-  int32_t ss_flags;  // int
-  uint32_t ss_size;  // size_t
-};
-
-struct x86_mcontext_t {
-  uint32_t gs;
-  uint32_t fs;
-  uint32_t es;
-  uint32_t ds;
-  uint32_t edi;
-  uint32_t esi;
-  uint32_t ebp;
-  uint32_t esp;
-  uint32_t ebx;
-  uint32_t edx;
-  uint32_t ecx;
-  uint32_t eax;
-  uint32_t trapno;
-  uint32_t err;
-  uint32_t eip;
-  uint32_t cs;
-  uint32_t efl;
-  uint32_t uesp;
-  uint32_t ss;
-  // Only care about the registers, skip everything else.
-};
-
-struct x86_ucontext_t {
-  uint32_t uc_flags;  // unsigned long
-  uint32_t uc_link;   // struct ucontext*
-  x86_stack_t uc_stack;
-  x86_mcontext_t uc_mcontext;
-  // Nothing else is used, so don't define it.
-};
-//-------------------------------------------------------------------
-
-//-------------------------------------------------------------------
-// X86_64 ucontext structures
-//-------------------------------------------------------------------
-struct x86_64_stack_t {
-  uint64_t ss_sp;    // void __user*
-  int32_t ss_flags;  // int
-  uint64_t ss_size;  // size_t
-};
-
-struct x86_64_mcontext_t {
-  uint64_t r8;
-  uint64_t r9;
-  uint64_t r10;
-  uint64_t r11;
-  uint64_t r12;
-  uint64_t r13;
-  uint64_t r14;
-  uint64_t r15;
-  uint64_t rdi;
-  uint64_t rsi;
-  uint64_t rbp;
-  uint64_t rbx;
-  uint64_t rdx;
-  uint64_t rax;
-  uint64_t rcx;
-  uint64_t rsp;
-  uint64_t rip;
-  uint64_t efl;
-  uint64_t csgsfs;
-  uint64_t err;
-  uint64_t trapno;
-  uint64_t oldmask;
-  uint64_t cr2;
-  // Only care about the registers, skip everything else.
-};
-
-struct x86_64_ucontext_t {
-  uint64_t uc_flags;  // unsigned long
-  uint64_t uc_link;   // struct ucontext*
-  x86_64_stack_t uc_stack;
-  x86_64_mcontext_t uc_mcontext;
-  // Nothing else is used, so don't define it.
-};
-//-------------------------------------------------------------------
-
-}  // namespace unwindstack
-
-#endif  // _LIBUNWINDSTACK_UCONTEXT_H
diff --git a/libunwindstack/UcontextArm.h b/libunwindstack/UcontextArm.h
new file mode 100644
index 0000000..8c94166
--- /dev/null
+++ b/libunwindstack/UcontextArm.h
@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _LIBUNWINDSTACK_UCONTEXT_ARM_H
+#define _LIBUNWINDSTACK_UCONTEXT_ARM_H
+
+#include <stdint.h>
+
+#include "MachineArm.h"
+
+namespace unwindstack {
+
+struct arm_stack_t {
+  uint32_t ss_sp;    // void __user*
+  int32_t ss_flags;  // int
+  uint32_t ss_size;  // size_t
+};
+
+struct arm_mcontext_t {
+  uint32_t trap_no;             // unsigned long
+  uint32_t error_code;          // unsigned long
+  uint32_t oldmask;             // unsigned long
+  uint32_t regs[ARM_REG_LAST];  // unsigned long
+  uint32_t cpsr;                // unsigned long
+  uint32_t fault_address;       // unsigned long
+};
+
+struct arm_ucontext_t {
+  uint32_t uc_flags;  // unsigned long
+  uint32_t uc_link;   // struct ucontext*
+  arm_stack_t uc_stack;
+  arm_mcontext_t uc_mcontext;
+  // Nothing else is used, so don't define it.
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_UCONTEXT_ARM_H
diff --git a/libunwindstack/UcontextArm64.h b/libunwindstack/UcontextArm64.h
new file mode 100644
index 0000000..655719f
--- /dev/null
+++ b/libunwindstack/UcontextArm64.h
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _LIBUNWINDSTACK_UCONTEXT_ARM64_H
+#define _LIBUNWINDSTACK_UCONTEXT_ARM64_H
+
+#include <stdint.h>
+
+#include "MachineArm64.h"
+
+namespace unwindstack {
+
+struct arm64_stack_t {
+  uint64_t ss_sp;    // void __user*
+  int32_t ss_flags;  // int
+  uint64_t ss_size;  // size_t
+};
+
+struct arm64_sigset_t {
+  uint64_t sig;  // unsigned long
+};
+
+struct arm64_mcontext_t {
+  uint64_t fault_address;         // __u64
+  uint64_t regs[ARM64_REG_LAST];  // __u64
+  uint64_t pstate;                // __u64
+  // Nothing else is used, so don't define it.
+};
+
+struct arm64_ucontext_t {
+  uint64_t uc_flags;  // unsigned long
+  uint64_t uc_link;   // struct ucontext*
+  arm64_stack_t uc_stack;
+  arm64_sigset_t uc_sigmask;
+  // The kernel adds extra padding after uc_sigmask to match glibc sigset_t on ARM64.
+  char __padding[128 - sizeof(arm64_sigset_t)];
+  // The full structure requires 16 byte alignment, but our partial structure
+  // doesn't, so force the alignment.
+  arm64_mcontext_t uc_mcontext __attribute__((aligned(16)));
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_UCONTEXT_ARM64_H
diff --git a/libunwindstack/User.h b/libunwindstack/UcontextX86.h
similarity index 62%
copy from libunwindstack/User.h
copy to libunwindstack/UcontextX86.h
index 53f7e50..f79d92b 100644
--- a/libunwindstack/User.h
+++ b/libunwindstack/UcontextX86.h
@@ -26,75 +26,52 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _LIBUNWINDSTACK_USER_H
-#define _LIBUNWINDSTACK_USER_H
+#ifndef _LIBUNWINDSTACK_UCONTEXT_X86_H
+#define _LIBUNWINDSTACK_UCONTEXT_X86_H
+
+#include <stdint.h>
+
+#include "MachineX86.h"
 
 namespace unwindstack {
 
-struct x86_user_regs {
-  uint32_t ebx;
-  uint32_t ecx;
-  uint32_t edx;
-  uint32_t esi;
+struct x86_stack_t {
+  uint32_t ss_sp;    // void __user*
+  int32_t ss_flags;  // int
+  uint32_t ss_size;  // size_t
+};
+
+struct x86_mcontext_t {
+  uint32_t gs;
+  uint32_t fs;
+  uint32_t es;
+  uint32_t ds;
   uint32_t edi;
+  uint32_t esi;
   uint32_t ebp;
-  uint32_t eax;
-  uint32_t xds;
-  uint32_t xes;
-  uint32_t xfs;
-  uint32_t xgs;
-  uint32_t orig_eax;
-  uint32_t eip;
-  uint32_t xcs;
-  uint32_t eflags;
   uint32_t esp;
-  uint32_t xss;
+  uint32_t ebx;
+  uint32_t edx;
+  uint32_t ecx;
+  uint32_t eax;
+  uint32_t trapno;
+  uint32_t err;
+  uint32_t eip;
+  uint32_t cs;
+  uint32_t efl;
+  uint32_t uesp;
+  uint32_t ss;
+  // Only care about the registers, skip everything else.
 };
 
-struct x86_64_user_regs {
-  uint64_t r15;
-  uint64_t r14;
-  uint64_t r13;
-  uint64_t r12;
-  uint64_t rbp;
-  uint64_t rbx;
-  uint64_t r11;
-  uint64_t r10;
-  uint64_t r9;
-  uint64_t r8;
-  uint64_t rax;
-  uint64_t rcx;
-  uint64_t rdx;
-  uint64_t rsi;
-  uint64_t rdi;
-  uint64_t orig_rax;
-  uint64_t rip;
-  uint64_t cs;
-  uint64_t eflags;
-  uint64_t rsp;
-  uint64_t ss;
-  uint64_t fs_base;
-  uint64_t gs_base;
-  uint64_t ds;
-  uint64_t es;
-  uint64_t fs;
-  uint64_t gs;
+struct x86_ucontext_t {
+  uint32_t uc_flags;  // unsigned long
+  uint32_t uc_link;   // struct ucontext*
+  x86_stack_t uc_stack;
+  x86_mcontext_t uc_mcontext;
+  // Nothing else is used, so don't define it.
 };
 
-struct arm_user_regs {
-  uint32_t regs[18];
-};
-
-struct arm64_user_regs {
-  uint64_t regs[31];
-  uint64_t sp;
-  uint64_t pc;
-  uint64_t pstate;
-};
-
-// The largest user structure.
-constexpr size_t MAX_USER_REGS_SIZE = sizeof(arm64_user_regs) + 10;
-
 }  // namespace unwindstack
 
-#endif  // _LIBUNWINDSTACK_USER_H
+#endif  // _LIBUNWINDSTACK_UCONTEXT_X86_H
diff --git a/libunwindstack/User.h b/libunwindstack/UcontextX86_64.h
similarity index 67%
copy from libunwindstack/User.h
copy to libunwindstack/UcontextX86_64.h
index 53f7e50..d689796 100644
--- a/libunwindstack/User.h
+++ b/libunwindstack/UcontextX86_64.h
@@ -26,75 +26,56 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _LIBUNWINDSTACK_USER_H
-#define _LIBUNWINDSTACK_USER_H
+#ifndef _LIBUNWINDSTACK_UCONTEXT_X86_64_H
+#define _LIBUNWINDSTACK_UCONTEXT_X86_64_H
+
+#include <stdint.h>
+
+#include "MachineX86_64.h"
 
 namespace unwindstack {
 
-struct x86_user_regs {
-  uint32_t ebx;
-  uint32_t ecx;
-  uint32_t edx;
-  uint32_t esi;
-  uint32_t edi;
-  uint32_t ebp;
-  uint32_t eax;
-  uint32_t xds;
-  uint32_t xes;
-  uint32_t xfs;
-  uint32_t xgs;
-  uint32_t orig_eax;
-  uint32_t eip;
-  uint32_t xcs;
-  uint32_t eflags;
-  uint32_t esp;
-  uint32_t xss;
+struct x86_64_stack_t {
+  uint64_t ss_sp;    // void __user*
+  int32_t ss_flags;  // int
+  uint64_t ss_size;  // size_t
 };
 
-struct x86_64_user_regs {
-  uint64_t r15;
-  uint64_t r14;
-  uint64_t r13;
+struct x86_64_mcontext_t {
+  uint64_t r8;
+  uint64_t r9;
+  uint64_t r10;
+  uint64_t r11;
   uint64_t r12;
+  uint64_t r13;
+  uint64_t r14;
+  uint64_t r15;
+  uint64_t rdi;
+  uint64_t rsi;
   uint64_t rbp;
   uint64_t rbx;
-  uint64_t r11;
-  uint64_t r10;
-  uint64_t r9;
-  uint64_t r8;
+  uint64_t rdx;
   uint64_t rax;
   uint64_t rcx;
-  uint64_t rdx;
-  uint64_t rsi;
-  uint64_t rdi;
-  uint64_t orig_rax;
-  uint64_t rip;
-  uint64_t cs;
-  uint64_t eflags;
   uint64_t rsp;
-  uint64_t ss;
-  uint64_t fs_base;
-  uint64_t gs_base;
-  uint64_t ds;
-  uint64_t es;
-  uint64_t fs;
-  uint64_t gs;
+  uint64_t rip;
+  uint64_t efl;
+  uint64_t csgsfs;
+  uint64_t err;
+  uint64_t trapno;
+  uint64_t oldmask;
+  uint64_t cr2;
+  // Only care about the registers, skip everything else.
 };
 
-struct arm_user_regs {
-  uint32_t regs[18];
+struct x86_64_ucontext_t {
+  uint64_t uc_flags;  // unsigned long
+  uint64_t uc_link;   // struct ucontext*
+  x86_64_stack_t uc_stack;
+  x86_64_mcontext_t uc_mcontext;
+  // Nothing else is used, so don't define it.
 };
 
-struct arm64_user_regs {
-  uint64_t regs[31];
-  uint64_t sp;
-  uint64_t pc;
-  uint64_t pstate;
-};
-
-// The largest user structure.
-constexpr size_t MAX_USER_REGS_SIZE = sizeof(arm64_user_regs) + 10;
-
 }  // namespace unwindstack
 
-#endif  // _LIBUNWINDSTACK_USER_H
+#endif  // _LIBUNWINDSTACK_UCONTEXT_X86_64_H
diff --git a/libunwindstack/Unwinder.cpp b/libunwindstack/Unwinder.cpp
index 3092a62..4ae365d 100644
--- a/libunwindstack/Unwinder.cpp
+++ b/libunwindstack/Unwinder.cpp
@@ -174,8 +174,7 @@
   if (frame_num >= frames_.size()) {
     return "";
   }
-  return FormatFrame(frames_[frame_num],
-                     regs_->MachineType() == EM_ARM || regs_->MachineType() == EM_386);
+  return FormatFrame(frames_[frame_num], regs_->Arch() == ARCH_ARM || regs_->Arch() == ARCH_X86);
 }
 
 std::string Unwinder::FormatFrame(const FrameData& frame, bool bits32) {
diff --git a/libunwindstack/UserArm.h b/libunwindstack/UserArm.h
new file mode 100644
index 0000000..7388c03
--- /dev/null
+++ b/libunwindstack/UserArm.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _LIBUNWINDSTACK_USER_ARM_H
+#define _LIBUNWINDSTACK_USER_ARM_H
+
+namespace unwindstack {
+
+struct arm_user_regs {
+  uint32_t regs[18];
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_USER_ARM_H
diff --git a/libunwindstack/User.h b/libunwindstack/UserArm64.h
similarity index 60%
copy from libunwindstack/User.h
copy to libunwindstack/UserArm64.h
index 53f7e50..d74983f 100644
--- a/libunwindstack/User.h
+++ b/libunwindstack/UserArm64.h
@@ -26,65 +26,11 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _LIBUNWINDSTACK_USER_H
-#define _LIBUNWINDSTACK_USER_H
+#ifndef _LIBUNWINDSTACK_USER_ARM64_H
+#define _LIBUNWINDSTACK_USER_ARM64_H
 
 namespace unwindstack {
 
-struct x86_user_regs {
-  uint32_t ebx;
-  uint32_t ecx;
-  uint32_t edx;
-  uint32_t esi;
-  uint32_t edi;
-  uint32_t ebp;
-  uint32_t eax;
-  uint32_t xds;
-  uint32_t xes;
-  uint32_t xfs;
-  uint32_t xgs;
-  uint32_t orig_eax;
-  uint32_t eip;
-  uint32_t xcs;
-  uint32_t eflags;
-  uint32_t esp;
-  uint32_t xss;
-};
-
-struct x86_64_user_regs {
-  uint64_t r15;
-  uint64_t r14;
-  uint64_t r13;
-  uint64_t r12;
-  uint64_t rbp;
-  uint64_t rbx;
-  uint64_t r11;
-  uint64_t r10;
-  uint64_t r9;
-  uint64_t r8;
-  uint64_t rax;
-  uint64_t rcx;
-  uint64_t rdx;
-  uint64_t rsi;
-  uint64_t rdi;
-  uint64_t orig_rax;
-  uint64_t rip;
-  uint64_t cs;
-  uint64_t eflags;
-  uint64_t rsp;
-  uint64_t ss;
-  uint64_t fs_base;
-  uint64_t gs_base;
-  uint64_t ds;
-  uint64_t es;
-  uint64_t fs;
-  uint64_t gs;
-};
-
-struct arm_user_regs {
-  uint32_t regs[18];
-};
-
 struct arm64_user_regs {
   uint64_t regs[31];
   uint64_t sp;
@@ -92,9 +38,6 @@
   uint64_t pstate;
 };
 
-// The largest user structure.
-constexpr size_t MAX_USER_REGS_SIZE = sizeof(arm64_user_regs) + 10;
-
 }  // namespace unwindstack
 
-#endif  // _LIBUNWINDSTACK_USER_H
+#endif  // _LIBUNWINDSTACK_USER_ARM64_H
diff --git a/libunwindstack/User.h b/libunwindstack/UserX86.h
similarity index 68%
copy from libunwindstack/User.h
copy to libunwindstack/UserX86.h
index 53f7e50..a040560 100644
--- a/libunwindstack/User.h
+++ b/libunwindstack/UserX86.h
@@ -26,8 +26,8 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _LIBUNWINDSTACK_USER_H
-#define _LIBUNWINDSTACK_USER_H
+#ifndef _LIBUNWINDSTACK_USER_X86_H
+#define _LIBUNWINDSTACK_USER_X86_H
 
 namespace unwindstack {
 
@@ -51,50 +51,6 @@
   uint32_t xss;
 };
 
-struct x86_64_user_regs {
-  uint64_t r15;
-  uint64_t r14;
-  uint64_t r13;
-  uint64_t r12;
-  uint64_t rbp;
-  uint64_t rbx;
-  uint64_t r11;
-  uint64_t r10;
-  uint64_t r9;
-  uint64_t r8;
-  uint64_t rax;
-  uint64_t rcx;
-  uint64_t rdx;
-  uint64_t rsi;
-  uint64_t rdi;
-  uint64_t orig_rax;
-  uint64_t rip;
-  uint64_t cs;
-  uint64_t eflags;
-  uint64_t rsp;
-  uint64_t ss;
-  uint64_t fs_base;
-  uint64_t gs_base;
-  uint64_t ds;
-  uint64_t es;
-  uint64_t fs;
-  uint64_t gs;
-};
-
-struct arm_user_regs {
-  uint32_t regs[18];
-};
-
-struct arm64_user_regs {
-  uint64_t regs[31];
-  uint64_t sp;
-  uint64_t pc;
-  uint64_t pstate;
-};
-
-// The largest user structure.
-constexpr size_t MAX_USER_REGS_SIZE = sizeof(arm64_user_regs) + 10;
-
 }  // namespace unwindstack
 
-#endif  // _LIBUNWINDSTACK_USER_H
+#endif  // _LIBUNWINDSTACK_USER_X86_H
diff --git a/libunwindstack/User.h b/libunwindstack/UserX86_64.h
similarity index 74%
rename from libunwindstack/User.h
rename to libunwindstack/UserX86_64.h
index 53f7e50..b80d201 100644
--- a/libunwindstack/User.h
+++ b/libunwindstack/UserX86_64.h
@@ -26,31 +26,11 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _LIBUNWINDSTACK_USER_H
-#define _LIBUNWINDSTACK_USER_H
+#ifndef _LIBUNWINDSTACK_USER_X86_64_H
+#define _LIBUNWINDSTACK_USER_X86_64_H
 
 namespace unwindstack {
 
-struct x86_user_regs {
-  uint32_t ebx;
-  uint32_t ecx;
-  uint32_t edx;
-  uint32_t esi;
-  uint32_t edi;
-  uint32_t ebp;
-  uint32_t eax;
-  uint32_t xds;
-  uint32_t xes;
-  uint32_t xfs;
-  uint32_t xgs;
-  uint32_t orig_eax;
-  uint32_t eip;
-  uint32_t xcs;
-  uint32_t eflags;
-  uint32_t esp;
-  uint32_t xss;
-};
-
 struct x86_64_user_regs {
   uint64_t r15;
   uint64_t r14;
@@ -81,20 +61,6 @@
   uint64_t gs;
 };
 
-struct arm_user_regs {
-  uint32_t regs[18];
-};
-
-struct arm64_user_regs {
-  uint64_t regs[31];
-  uint64_t sp;
-  uint64_t pc;
-  uint64_t pstate;
-};
-
-// The largest user structure.
-constexpr size_t MAX_USER_REGS_SIZE = sizeof(arm64_user_regs) + 10;
-
 }  // namespace unwindstack
 
-#endif  // _LIBUNWINDSTACK_USER_H
+#endif  // _LIBUNWINDSTACK_USER_X86_64_H
diff --git a/libunwindstack/include/unwindstack/Elf.h b/libunwindstack/include/unwindstack/Elf.h
index d9ea9c4..d27727b 100644
--- a/libunwindstack/include/unwindstack/Elf.h
+++ b/libunwindstack/include/unwindstack/Elf.h
@@ -36,6 +36,14 @@
 struct MapInfo;
 class Regs;
 
+enum ArchEnum : uint8_t {
+  ARCH_UNKNOWN = 0,
+  ARCH_ARM,
+  ARCH_ARM64,
+  ARCH_X86,
+  ARCH_X86_64,
+};
+
 class Elf {
  public:
   Elf(Memory* memory) : memory_(memory) {}
@@ -64,6 +72,8 @@
 
   uint8_t class_type() { return class_type_; }
 
+  ArchEnum arch() { return arch_; }
+
   Memory* memory() { return memory_.get(); }
 
   ElfInterface* interface() { return interface_.get(); }
@@ -83,6 +93,7 @@
   std::unique_ptr<Memory> memory_;
   uint32_t machine_type_;
   uint8_t class_type_;
+  ArchEnum arch_;
   // Protect calls that can modify internal state of the interface object.
   std::mutex lock_;
 
diff --git a/libunwindstack/include/unwindstack/Regs.h b/libunwindstack/include/unwindstack/Regs.h
index 6576e4c..7025fcf 100644
--- a/libunwindstack/include/unwindstack/Regs.h
+++ b/libunwindstack/include/unwindstack/Regs.h
@@ -27,10 +27,8 @@
 
 // Forward declarations.
 class Elf;
-struct MapInfo;
+enum ArchEnum : uint8_t;
 class Memory;
-struct x86_ucontext_t;
-struct x86_64_ucontext_t;
 
 class Regs {
  public:
@@ -51,7 +49,7 @@
       : total_regs_(total_regs), sp_reg_(sp_reg), return_loc_(return_loc) {}
   virtual ~Regs() = default;
 
-  virtual uint32_t MachineType() = 0;
+  virtual ArchEnum Arch() = 0;
 
   virtual void* RawData() = 0;
   virtual uint64_t pc() = 0;
@@ -70,9 +68,9 @@
   uint16_t sp_reg() { return sp_reg_; }
   uint16_t total_regs() { return total_regs_; }
 
-  static uint32_t CurrentMachineType();
+  static ArchEnum CurrentArch();
   static Regs* RemoteGet(pid_t pid);
-  static Regs* CreateFromUcontext(uint32_t machine_type, void* ucontext);
+  static Regs* CreateFromUcontext(ArchEnum arch, void* ucontext);
   static Regs* CreateFromLocal();
 
  protected:
@@ -110,82 +108,6 @@
   std::vector<AddressType> regs_;
 };
 
-class RegsArm : public RegsImpl<uint32_t> {
- public:
-  RegsArm();
-  virtual ~RegsArm() = default;
-
-  virtual uint32_t MachineType() override final;
-
-  uint64_t GetAdjustedPc(uint64_t rel_pc, Elf* elf) override;
-
-  void SetFromRaw() override;
-
-  bool SetPcFromReturnAddress(Memory* process_memory) override;
-
-  bool StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) override;
-
-  virtual void IterateRegisters(std::function<void(const char*, uint64_t)>) override final;
-};
-
-class RegsArm64 : public RegsImpl<uint64_t> {
- public:
-  RegsArm64();
-  virtual ~RegsArm64() = default;
-
-  virtual uint32_t MachineType() override final;
-
-  uint64_t GetAdjustedPc(uint64_t rel_pc, Elf* elf) override;
-
-  void SetFromRaw() override;
-
-  bool SetPcFromReturnAddress(Memory* process_memory) override;
-
-  bool StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) override;
-
-  virtual void IterateRegisters(std::function<void(const char*, uint64_t)>) override final;
-};
-
-class RegsX86 : public RegsImpl<uint32_t> {
- public:
-  RegsX86();
-  virtual ~RegsX86() = default;
-
-  virtual uint32_t MachineType() override final;
-
-  uint64_t GetAdjustedPc(uint64_t rel_pc, Elf* elf) override;
-
-  void SetFromRaw() override;
-
-  bool SetPcFromReturnAddress(Memory* process_memory) override;
-
-  bool StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) override;
-
-  void SetFromUcontext(x86_ucontext_t* ucontext);
-
-  virtual void IterateRegisters(std::function<void(const char*, uint64_t)>) override final;
-};
-
-class RegsX86_64 : public RegsImpl<uint64_t> {
- public:
-  RegsX86_64();
-  virtual ~RegsX86_64() = default;
-
-  virtual uint32_t MachineType() override final;
-
-  uint64_t GetAdjustedPc(uint64_t rel_pc, Elf* elf) override;
-
-  void SetFromRaw() override;
-
-  bool SetPcFromReturnAddress(Memory* process_memory) override;
-
-  bool StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) override;
-
-  void SetFromUcontext(x86_64_ucontext_t* ucontext);
-
-  virtual void IterateRegisters(std::function<void(const char*, uint64_t)>) override final;
-};
-
 }  // namespace unwindstack
 
 #endif  // _LIBUNWINDSTACK_REGS_H
diff --git a/libunwindstack/include/unwindstack/RegsArm.h b/libunwindstack/include/unwindstack/RegsArm.h
new file mode 100644
index 0000000..b5d344b
--- /dev/null
+++ b/libunwindstack/include/unwindstack/RegsArm.h
@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBUNWINDSTACK_REGS_ARM_H
+#define _LIBUNWINDSTACK_REGS_ARM_H
+
+#include <stdint.h>
+
+#include <functional>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/Regs.h>
+
+namespace unwindstack {
+
+// Forward declarations.
+class Memory;
+
+class RegsArm : public RegsImpl<uint32_t> {
+ public:
+  RegsArm();
+  virtual ~RegsArm() = default;
+
+  virtual ArchEnum Arch() override final;
+
+  uint64_t GetAdjustedPc(uint64_t rel_pc, Elf* elf) override;
+
+  void SetFromRaw() override;
+
+  bool SetPcFromReturnAddress(Memory* process_memory) override;
+
+  bool StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) override;
+
+  virtual void IterateRegisters(std::function<void(const char*, uint64_t)>) override final;
+
+  static Regs* Read(void* data);
+
+  static Regs* CreateFromUcontext(void* ucontext);
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_REGS_ARM_H
diff --git a/libunwindstack/include/unwindstack/RegsArm64.h b/libunwindstack/include/unwindstack/RegsArm64.h
new file mode 100644
index 0000000..30e626c
--- /dev/null
+++ b/libunwindstack/include/unwindstack/RegsArm64.h
@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBUNWINDSTACK_REGS_ARM64_H
+#define _LIBUNWINDSTACK_REGS_ARM64_H
+
+#include <stdint.h>
+
+#include <functional>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/Regs.h>
+
+namespace unwindstack {
+
+// Forward declarations.
+class Memory;
+
+class RegsArm64 : public RegsImpl<uint64_t> {
+ public:
+  RegsArm64();
+  virtual ~RegsArm64() = default;
+
+  virtual ArchEnum Arch() override final;
+
+  uint64_t GetAdjustedPc(uint64_t rel_pc, Elf* elf) override;
+
+  void SetFromRaw() override;
+
+  bool SetPcFromReturnAddress(Memory* process_memory) override;
+
+  bool StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) override;
+
+  virtual void IterateRegisters(std::function<void(const char*, uint64_t)>) override final;
+
+  static Regs* Read(void* data);
+
+  static Regs* CreateFromUcontext(void* ucontext);
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_REGS_ARM64_H
diff --git a/libunwindstack/include/unwindstack/RegsX86.h b/libunwindstack/include/unwindstack/RegsX86.h
new file mode 100644
index 0000000..a695bbf
--- /dev/null
+++ b/libunwindstack/include/unwindstack/RegsX86.h
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBUNWINDSTACK_REGS_X86_H
+#define _LIBUNWINDSTACK_REGS_X86_H
+
+#include <stdint.h>
+
+#include <functional>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/Regs.h>
+
+namespace unwindstack {
+
+// Forward declarations.
+class Memory;
+struct x86_ucontext_t;
+
+class RegsX86 : public RegsImpl<uint32_t> {
+ public:
+  RegsX86();
+  virtual ~RegsX86() = default;
+
+  virtual ArchEnum Arch() override final;
+
+  uint64_t GetAdjustedPc(uint64_t rel_pc, Elf* elf) override;
+
+  void SetFromRaw() override;
+
+  bool SetPcFromReturnAddress(Memory* process_memory) override;
+
+  bool StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) override;
+
+  void SetFromUcontext(x86_ucontext_t* ucontext);
+
+  virtual void IterateRegisters(std::function<void(const char*, uint64_t)>) override final;
+
+  static Regs* Read(void* data);
+
+  static Regs* CreateFromUcontext(void* ucontext);
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_REGS_X86_H
diff --git a/libunwindstack/include/unwindstack/RegsX86_64.h b/libunwindstack/include/unwindstack/RegsX86_64.h
new file mode 100644
index 0000000..23a3f20
--- /dev/null
+++ b/libunwindstack/include/unwindstack/RegsX86_64.h
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBUNWINDSTACK_REGS_X86_64_H
+#define _LIBUNWINDSTACK_REGS_X86_64_H
+
+#include <stdint.h>
+
+#include <functional>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/Regs.h>
+
+namespace unwindstack {
+
+// Forward declarations.
+class Memory;
+struct x86_64_ucontext_t;
+
+class RegsX86_64 : public RegsImpl<uint64_t> {
+ public:
+  RegsX86_64();
+  virtual ~RegsX86_64() = default;
+
+  virtual ArchEnum Arch() override final;
+
+  uint64_t GetAdjustedPc(uint64_t rel_pc, Elf* elf) override;
+
+  void SetFromRaw() override;
+
+  bool SetPcFromReturnAddress(Memory* process_memory) override;
+
+  bool StepIfSignalHandler(uint64_t rel_pc, Elf* elf, Memory* process_memory) override;
+
+  void SetFromUcontext(x86_64_ucontext_t* ucontext);
+
+  virtual void IterateRegisters(std::function<void(const char*, uint64_t)>) override final;
+
+  static Regs* Read(void* data);
+
+  static Regs* CreateFromUcontext(void* ucontext);
+};
+
+}  // namespace unwindstack
+
+#endif  // _LIBUNWINDSTACK_REGS_X86_64_H
diff --git a/libunwindstack/tests/ArmExidxDecodeTest.cpp b/libunwindstack/tests/ArmExidxDecodeTest.cpp
index 94cb493..8d6d00d 100644
--- a/libunwindstack/tests/ArmExidxDecodeTest.cpp
+++ b/libunwindstack/tests/ArmExidxDecodeTest.cpp
@@ -24,7 +24,7 @@
 #include <gtest/gtest.h>
 
 #include <unwindstack/Log.h>
-#include <unwindstack/Regs.h>
+#include <unwindstack/RegsArm.h>
 
 #include "ArmExidx.h"
 
diff --git a/libunwindstack/tests/ElfInterfaceArmTest.cpp b/libunwindstack/tests/ElfInterfaceArmTest.cpp
index 4b621c9..5f7cf60 100644
--- a/libunwindstack/tests/ElfInterfaceArmTest.cpp
+++ b/libunwindstack/tests/ElfInterfaceArmTest.cpp
@@ -20,10 +20,10 @@
 
 #include <vector>
 
-#include <unwindstack/Regs.h>
+#include <unwindstack/RegsArm.h>
 
 #include "ElfInterfaceArm.h"
-#include "Machine.h"
+#include "MachineArm.h"
 
 #include "ElfFake.h"
 #include "MemoryFake.h"
diff --git a/libunwindstack/tests/ElfTest.cpp b/libunwindstack/tests/ElfTest.cpp
index afd113d..00192f1 100644
--- a/libunwindstack/tests/ElfTest.cpp
+++ b/libunwindstack/tests/ElfTest.cpp
@@ -25,6 +25,7 @@
 
 #include <unwindstack/Elf.h>
 #include <unwindstack/MapInfo.h>
+#include <unwindstack/RegsArm.h>
 
 #include "ElfFake.h"
 #include "ElfTestUtils.h"
diff --git a/libunwindstack/tests/RegsFake.h b/libunwindstack/tests/RegsFake.h
index fedaf87..3c5af4a 100644
--- a/libunwindstack/tests/RegsFake.h
+++ b/libunwindstack/tests/RegsFake.h
@@ -19,6 +19,7 @@
 
 #include <stdint.h>
 
+#include <unwindstack/Elf.h>
 #include <unwindstack/Memory.h>
 #include <unwindstack/Regs.h>
 
@@ -30,7 +31,7 @@
       : Regs(total_regs, sp_reg, Regs::Location(Regs::LOCATION_UNKNOWN, 0)) {}
   virtual ~RegsFake() = default;
 
-  uint32_t MachineType() override { return fake_type_; }
+  ArchEnum Arch() override { return fake_arch_; }
   void* RawData() override { return nullptr; }
   uint64_t pc() override { return fake_pc_; }
   uint64_t sp() override { return fake_sp_; }
@@ -50,14 +51,14 @@
 
   void SetFromRaw() override {}
 
-  void FakeSetMachineType(uint32_t type) { fake_type_ = type; }
+  void FakeSetArch(ArchEnum arch) { fake_arch_ = arch; }
   void FakeSetPc(uint64_t pc) { fake_pc_ = pc; }
   void FakeSetSp(uint64_t sp) { fake_sp_ = sp; }
   void FakeSetReturnAddress(uint64_t return_address) { fake_return_address_ = return_address; }
   void FakeSetReturnAddressValid(bool valid) { fake_return_address_valid_ = valid; }
 
  private:
-  uint32_t fake_type_ = 0;
+  ArchEnum fake_arch_ = ARCH_UNKNOWN;
   uint64_t fake_pc_ = 0;
   uint64_t fake_sp_ = 0;
   bool fake_return_address_valid_ = false;
@@ -71,7 +72,7 @@
       : RegsImpl<TypeParam>(total_regs, sp_reg, Regs::Location(Regs::LOCATION_UNKNOWN, 0)) {}
   virtual ~RegsImplFake() = default;
 
-  uint32_t MachineType() override { return 0; }
+  ArchEnum Arch() override { return ARCH_UNKNOWN; }
 
   uint64_t GetAdjustedPc(uint64_t, Elf*) override { return 0; }
   void SetFromRaw() override {}
diff --git a/libunwindstack/tests/RegsIterateTest.cpp b/libunwindstack/tests/RegsIterateTest.cpp
index c8d1d98..0cb70ba 100644
--- a/libunwindstack/tests/RegsIterateTest.cpp
+++ b/libunwindstack/tests/RegsIterateTest.cpp
@@ -25,9 +25,15 @@
 #include <unwindstack/Elf.h>
 #include <unwindstack/ElfInterface.h>
 #include <unwindstack/MapInfo.h>
-#include <unwindstack/Regs.h>
+#include <unwindstack/RegsArm.h>
+#include <unwindstack/RegsArm64.h>
+#include <unwindstack/RegsX86.h>
+#include <unwindstack/RegsX86_64.h>
 
-#include "Machine.h"
+#include "MachineArm.h"
+#include "MachineArm64.h"
+#include "MachineX86.h"
+#include "MachineX86_64.h"
 
 namespace unwindstack {
 
diff --git a/libunwindstack/tests/RegsStepIfSignalHandlerTest.cpp b/libunwindstack/tests/RegsStepIfSignalHandlerTest.cpp
index 85192d5..ae57caf 100644
--- a/libunwindstack/tests/RegsStepIfSignalHandlerTest.cpp
+++ b/libunwindstack/tests/RegsStepIfSignalHandlerTest.cpp
@@ -19,9 +19,15 @@
 #include <gtest/gtest.h>
 
 #include <unwindstack/Elf.h>
-#include <unwindstack/Regs.h>
+#include <unwindstack/RegsArm.h>
+#include <unwindstack/RegsArm64.h>
+#include <unwindstack/RegsX86.h>
+#include <unwindstack/RegsX86_64.h>
 
-#include "Machine.h"
+#include "MachineArm.h"
+#include "MachineArm64.h"
+#include "MachineX86.h"
+#include "MachineX86_64.h"
 
 #include "MemoryFake.h"
 
diff --git a/libunwindstack/tests/RegsTest.cpp b/libunwindstack/tests/RegsTest.cpp
index 3320f77..a932973 100644
--- a/libunwindstack/tests/RegsTest.cpp
+++ b/libunwindstack/tests/RegsTest.cpp
@@ -21,7 +21,10 @@
 #include <unwindstack/Elf.h>
 #include <unwindstack/ElfInterface.h>
 #include <unwindstack/MapInfo.h>
-#include <unwindstack/Regs.h>
+#include <unwindstack/RegsArm.h>
+#include <unwindstack/RegsArm64.h>
+#include <unwindstack/RegsX86.h>
+#include <unwindstack/RegsX86_64.h>
 
 #include "ElfFake.h"
 #include "MemoryFake.h"
@@ -212,4 +215,18 @@
   EXPECT_EQ(0x4900000000U, x86_64.pc());
 }
 
+TEST_F(RegsTest, machine_type) {
+  RegsArm arm_regs;
+  EXPECT_EQ(ARCH_ARM, arm_regs.Arch());
+
+  RegsArm64 arm64_regs;
+  EXPECT_EQ(ARCH_ARM64, arm64_regs.Arch());
+
+  RegsX86 x86_regs;
+  EXPECT_EQ(ARCH_X86, x86_regs.Arch());
+
+  RegsX86_64 x86_64_regs;
+  EXPECT_EQ(ARCH_X86_64, x86_64_regs.Arch());
+}
+
 }  // namespace unwindstack
diff --git a/libunwindstack/tests/UnwindOfflineTest.cpp b/libunwindstack/tests/UnwindOfflineTest.cpp
index d24abe4..962f744 100644
--- a/libunwindstack/tests/UnwindOfflineTest.cpp
+++ b/libunwindstack/tests/UnwindOfflineTest.cpp
@@ -27,10 +27,12 @@
 
 #include <unwindstack/Maps.h>
 #include <unwindstack/Memory.h>
-#include <unwindstack/Regs.h>
+#include <unwindstack/RegsArm.h>
+#include <unwindstack/RegsArm64.h>
 #include <unwindstack/Unwinder.h>
 
-#include "Machine.h"
+#include "MachineArm.h"
+#include "MachineArm64.h"
 
 #include "ElfTestUtils.h"
 
@@ -73,7 +75,7 @@
   BufferMaps maps(buffer.data());
   ASSERT_TRUE(maps.Parse());
 
-  ASSERT_EQ(static_cast<uint32_t>(EM_ARM), regs.MachineType());
+  ASSERT_EQ(ARCH_ARM, regs.Arch());
 
   std::shared_ptr<Memory> process_memory(memory);
 
@@ -125,7 +127,7 @@
   BufferMaps maps(buffer.data());
   ASSERT_TRUE(maps.Parse());
 
-  ASSERT_EQ(static_cast<uint32_t>(EM_AARCH64), regs.MachineType());
+  ASSERT_EQ(ARCH_ARM64, regs.Arch());
 
   std::shared_ptr<Memory> process_memory(memory);
 
diff --git a/libunwindstack/tests/UnwindTest.cpp b/libunwindstack/tests/UnwindTest.cpp
index b372fd0..242cc6a 100644
--- a/libunwindstack/tests/UnwindTest.cpp
+++ b/libunwindstack/tests/UnwindTest.cpp
@@ -250,7 +250,7 @@
 
   LocalMaps maps;
   ASSERT_TRUE(maps.Parse());
-  std::unique_ptr<Regs> regs(Regs::CreateFromUcontext(Regs::CurrentMachineType(), ucontext));
+  std::unique_ptr<Regs> regs(Regs::CreateFromUcontext(Regs::CurrentArch(), ucontext));
 
   VerifyUnwind(getpid(), &maps, regs.get(), kFunctionOrder);
 
diff --git a/libunwindstack/tests/UnwinderTest.cpp b/libunwindstack/tests/UnwinderTest.cpp
index 098459e..71103b4 100644
--- a/libunwindstack/tests/UnwinderTest.cpp
+++ b/libunwindstack/tests/UnwinderTest.cpp
@@ -95,7 +95,7 @@
 
   void SetUp() override {
     ElfInterfaceFake::FakeClear();
-    regs_.FakeSetMachineType(EM_ARM);
+    regs_.FakeSetArch(ARCH_ARM);
     regs_.FakeSetReturnAddressValid(false);
   }
 
@@ -702,14 +702,14 @@
 
   ASSERT_EQ(1U, unwinder.NumFrames());
 
-  regs_.FakeSetMachineType(EM_ARM);
+  regs_.FakeSetArch(ARCH_ARM);
   EXPECT_EQ("  #00 pc 00001300  /system/fake/libc.so (Frame0+10)", unwinder.FormatFrame(0));
-  regs_.FakeSetMachineType(EM_386);
+  regs_.FakeSetArch(ARCH_X86);
   EXPECT_EQ("  #00 pc 00001300  /system/fake/libc.so (Frame0+10)", unwinder.FormatFrame(0));
 
-  regs_.FakeSetMachineType(EM_AARCH64);
+  regs_.FakeSetArch(ARCH_ARM64);
   EXPECT_EQ("  #00 pc 0000000000001300  /system/fake/libc.so (Frame0+10)", unwinder.FormatFrame(0));
-  regs_.FakeSetMachineType(EM_X86_64);
+  regs_.FakeSetArch(ARCH_X86_64);
   EXPECT_EQ("  #00 pc 0000000000001300  /system/fake/libc.so (Frame0+10)", unwinder.FormatFrame(0));
 
   EXPECT_EQ("", unwinder.FormatFrame(1));
diff --git a/libunwindstack/tools/unwind.cpp b/libunwindstack/tools/unwind.cpp
index f2530d7..7896279 100644
--- a/libunwindstack/tools/unwind.cpp
+++ b/libunwindstack/tools/unwind.cpp
@@ -63,17 +63,17 @@
   }
 
   printf("ABI: ");
-  switch (regs->MachineType()) {
-    case EM_ARM:
+  switch (regs->Arch()) {
+    case unwindstack::ARCH_ARM:
       printf("arm");
       break;
-    case EM_386:
+    case unwindstack::ARCH_X86:
       printf("x86");
       break;
-    case EM_AARCH64:
+    case unwindstack::ARCH_ARM64:
       printf("arm64");
       break;
-    case EM_X86_64:
+    case unwindstack::ARCH_X86_64:
       printf("x86_64");
       break;
     default: