Add signal handling to the register object.

- Add the StepIfSignalHandler function to the Regs object that checks
  if the code is in a signal handler.
- Add tests for new code, also add a test that unwinds through a signal
  handler.
- Slight modification to Elf to fail if a bad machine type is encountered.
  Add tests for this.

Bug: 23762183

Test: Ran unit tests.
Change-Id: Idafa1105d00b91a9343d7464ac9ed1cb95830963
diff --git a/libunwindstack/tests/ElfTest.cpp b/libunwindstack/tests/ElfTest.cpp
index 72ceb85..ed1be3b 100644
--- a/libunwindstack/tests/ElfTest.cpp
+++ b/libunwindstack/tests/ElfTest.cpp
@@ -26,6 +26,7 @@
 #include <unwindstack/MapInfo.h>
 
 #include "ElfTestUtils.h"
+#include "LogFake.h"
 #include "MemoryFake.h"
 
 #if !defined(PT_ARM_EXIDX)
@@ -131,6 +132,32 @@
   ASSERT_FALSE(elf.Step(0, nullptr, nullptr));
 }
 
+TEST_F(ElfTest, elf32_invalid_machine) {
+  Elf elf(memory_);
+
+  InitElf32(EM_PPC);
+
+  ResetLogs();
+  ASSERT_FALSE(elf.Init());
+
+  ASSERT_EQ("", GetFakeLogBuf());
+  ASSERT_EQ("4 unwind 32 bit elf that is neither arm nor x86: e_machine = 20\n\n",
+            GetFakeLogPrint());
+}
+
+TEST_F(ElfTest, elf64_invalid_machine) {
+  Elf elf(memory_);
+
+  InitElf64(EM_PPC64);
+
+  ResetLogs();
+  ASSERT_FALSE(elf.Init());
+
+  ASSERT_EQ("", GetFakeLogBuf());
+  ASSERT_EQ("4 unwind 64 bit elf that is neither aarch64 nor x86_64: e_machine = 21\n\n",
+            GetFakeLogPrint());
+}
+
 TEST_F(ElfTest, elf_arm) {
   Elf elf(memory_);