Remove exidx wrapper in arm builds

Removes exidx wrapper from arm32 unwinds. The wrapper caused issues
with unwinding crashes in official test bots, crbug/1078588. Since we
are not using libunwind to unwind due to other crashes, this wrapper can
be removed.

BUG=1078588

Change-Id: Ifc6832345a715e75a4344f4dcdd1b570d6f0626b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2330743Reviewed-by: oysteine <oysteine@chromium.org>
Commit-Queue: ssid <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808093}

services/tracing/public/cpp/BUILD.gn

@@ -13,10 +13,6 @@ buildflag_header("buildflags") {
   flags = [ "ENABLE_LOADER_LOCK_SAMPLING=$enable_loader_lock_sampling" ]
 }
 
-config("wrap_find_exidx") {
-  ldflags = [ "-Wl,-wrap,dl_unwind_find_exidx" ]
-}
-
 source_set("traced_process") {
   sources = [
     "traced_process.cc",
@@ -162,9 +158,6 @@ target(tracing_lib_type, "cpp") {
       ]
       deps += [ "//buildtools/third_party/libunwind" ]
       include_dirs = [ "//buildtools/third_party/libunwind/trunk/include" ]
-
-      # stack_unwinder_android.cc overrides the dl_unwind_find_exidx function.
-      all_dependent_configs += [ ":wrap_find_exidx" ]
     }
   }  # !is_ios && !is_nacl
 }

services/tracing/public/cpp/stack_sampling/stack_unwinder_android.cc

@@ -440,43 +440,8 @@ static void ThreadSignalHandler(int n, siginfo_t* siginfo, void* sigcontext) {
   *params->success = true;
 }
 
-// ARM EXIDX table contains addresses in sorted order with unwind data, each of
-// 32 bits.
-struct FakeExidx {
-  uintptr_t pc;
-  uintptr_t index_data;
-};
-
 }  // namespace
 
-extern "C" {
-
-_Unwind_Ptr __real_dl_unwind_find_exidx(_Unwind_Ptr, int*);
-
-// Override the default |dl_unwind_find_exidx| function used by libunwind to
-// give a fake unwind table just for the handler function. Otherwise call the
-// original function. Libunwind marks the cursor invalid if it finds even one
-// frame without unwind info. Mocking the info keeps the unwind cursor valid
-// after unwind_init_local() within ThreadSignalHandler().
-__attribute__((visibility("default"), noinline)) _Unwind_Ptr
-__wrap_dl_unwind_find_exidx(_Unwind_Ptr pc, int* length) {
-  if (!CFIBacktraceAndroid::is_chrome_address(pc)) {
-    return __real_dl_unwind_find_exidx(pc, length);
-  }
-  // Fake exidx table that is passed to libunwind to work with chrome functions.
-  // 0x80000000 has high bit set to 1. This means the unwind data is inline and
-  // not in exception table (section 5 EHABI). 0 on the second high byte causes
-  // a 0 proceedure to be lsda. But this is never executed since the pc and sp
-  // will be overridden, before calling unw_step.
-  static const FakeExidx chrome_exidx_data[] = {
-      {CFIBacktraceAndroid::executable_start_addr(), 0x80000000},
-      {CFIBacktraceAndroid::executable_end_addr(), 0x80000000}};
-  *length = base::size(chrome_exidx_data);
-  return reinterpret_cast<_Unwind_Ptr>(chrome_exidx_data);
-}
-
-}  // extern "C"
-
 namespace tracing {
 
 // static