AIX: Disable backtrace API call

src/base/debug/stack_trace_posix.cc

Index: src/base/debug/stack_trace_posix.cc
diff --git a/src/base/debug/stack_trace_posix.cc b/src/base/debug/stack_trace_posix.cc
index cbd722d35cda9e12a33898c912f4da4794148599..c4bccc81c81d02f63d080f48f1231ee145318443 100644
--- a/src/base/debug/stack_trace_posix.cc
+++ b/src/base/debug/stack_trace_posix.cc
@@ -145,6 +145,9 @@ void ProcessBacktrace(void* const* trace, size_t size,
 
   bool printed = false;
 
+// NOTE: backtrace_symbol API is not supported on AIX and there is no
+// equivalent user-mode API. For now disabling the call to the API

[rmcilroy, 2016/09/08 10:10:10]

No need for the comment (there are probably other platforms in a similar
situation and this comment will get stale when #ifdefing out other platforms).

+#if !V8_OS_AIX

[rmcilroy, 2016/09/08 10:10:10]

Could you instead ifdef out the whole of ProcessBacktrace and the calls to it
(similarly to how __ulibc__ is treated in the chromium version of the file:
https://cs.chromium.org/chromium/src/base/debug/stack_trace_posix.cc?type=cs&...

   // Below part is async-signal unsafe (uses malloc), so execute it only
   // when we are not executing the signal handler.
   if (in_signal_handler == 0) {
@@ -162,6 +165,7 @@ void ProcessBacktrace(void* const* trace, size_t size,
       printed = true;
     }
   }
+#endif
 
   if (!printed) {
     for (size_t i = 0; i < size; ++i) {
@@ -356,12 +360,18 @@ void DisableSignalStackDump() {
 }
 
 StackTrace::StackTrace() {
+// NOTE: backtrace API is not supported on AIX and there is no
+// equivalent user-mode API. For now disabling the call to the API

[rmcilroy, 2016/09/08 10:10:10]

No need for the comment

+#if V8_OS_AIX

[rmcilroy, 2016/09/08 10:10:10]

Could you make this #if !V8_OS_AIX and swap the branches around.

+  count_ = 0;
+#else
   // NOTE: This code MUST be async-signal safe (it's used by in-process
   // stack dumping signal handler). NO malloc or stdio is allowed here.
 
   // Though the backtrace API man page does not list any possible negative
   // return values, we take no chance.
   count_ = static_cast<size_t>(backtrace(trace_, arraysize(trace_)));
+#endif
 }
 
 void StackTrace::Print() const {