libunwindstack: Add Memory::ReadTag() function for reading memory tags.
This uses an experimental Linux kernel API for reading the tags across
processes using ptrace.
Bug: 135772972
Test: Unit tests pass.
Change-Id: Ib1a09d9219166011de80cf250b756bb8a4bcdb0a
diff --git a/libunwindstack/MemoryMte.cpp b/libunwindstack/MemoryMte.cpp
new file mode 100644
index 0000000..d1d0ebc
--- /dev/null
+++ b/libunwindstack/MemoryMte.cpp
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+#if defined(ANDROID_EXPERIMENTAL_MTE)
+
+#include <sys/ptrace.h>
+
+#include <bionic/mte.h>
+#include <bionic/mte_kernel.h>
+
+#include "MemoryLocal.h"
+#include "MemoryRemote.h"
+
+namespace unwindstack {
+
+long MemoryRemote::ReadTag(uint64_t addr) {
+#if defined(__aarch64__)
+ return ptrace(PTRACE_PEEKTAG, pid_, (void*)addr, nullptr);
+#else
+ (void)addr;
+ return -1;
+#endif
+}
+
+long MemoryLocal::ReadTag(uint64_t addr) {
+#if defined(__aarch64__)
+ // Check that the memory is readable first. This is racy with the ldg but there's not much
+ // we can do about it.
+ char data;
+ if (!mte_supported() || !Read(addr, &data, 1)) {
+ return -1;
+ }
+
+ __asm__ __volatile__(".arch_extension mte; ldg %0, [%0]" : "+r"(addr) : : "memory");
+ return (addr >> 56) & 0xf;
+#else
+ (void)addr;
+ return -1;
+#endif
+}
+
+} // namespace unwindstack
+
+#endif