Add method to detect remote read function to use.

The process_vm_read function is much faster than ptrace, but sometimes
that will not work on a remote process. Modify the libunwindstack
MemoryRemote object to figure out which one it can use.

Wrote new unit test to verify this checking behavior.

Modify libbacktrace so that the read from libunwind is used instead of
using the default ptrace calls.

Add some benchmarks to libbacktrace to compare the two different methods.

Test: Ran unit tests libbacktrace/libunwindstack/debuggerd.
Test: Ran debuggerd -b <SYSTEM_SERVER_PID>
Test: Ran debuggerd -b <MEDIACODEC PID>
Test: Ran debuggerd -b <RANDOM_PID>
Test: Used crasher to create tombstones and verified stack data is
Test: dumped properly.
Change-Id: If75ca238289532dd8e1de430d569cabb2523380a

1 files changed, 5 insertions, 1 deletions

diff --git a/libbacktrace/UnwindStack.cpp b/libbacktrace/UnwindStack.cpp
index d61384ef1..56a6c6889 100644
--- a/libbacktrace/UnwindStack.cpp
+++ b/libbacktrace/UnwindStack.cpp
@@ -108,7 +108,7 @@ bool UnwindStackCurrent::UnwindFromContext(size_t num_ignore_frames, ucontext_t*
 }
 
 UnwindStackPtrace::UnwindStackPtrace(pid_t pid, pid_t tid, BacktraceMap* map)
-    : BacktracePtrace(pid, tid, map) {}
+    : BacktracePtrace(pid, tid, map), memory_(pid) {}
 
 std::string UnwindStackPtrace::GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset) {
   return GetMap()->GetFunctionName(pc, offset);
@@ -125,3 +125,7 @@ bool UnwindStackPtrace::Unwind(size_t num_ignore_frames, ucontext_t* context) {
   error_ = BACKTRACE_UNWIND_NO_ERROR;
   return Backtrace::Unwind(regs.get(), GetMap(), &frames_, num_ignore_frames, nullptr);
 }
+
+size_t UnwindStackPtrace::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
+  return memory_.Read(addr, buffer, bytes);
+}