1 files changed, 74 insertions, 46 deletions

diff --git a/third_party/tcmalloc/chromium/src/stacktrace_libunwind-inl.h b/third_party/tcmalloc/chromium/src/stacktrace_libunwind-inl.h
index a1d5249..d9d829a 100644
--- a/third_party/tcmalloc/chromium/src/stacktrace_libunwind-inl.h
+++ b/third_party/tcmalloc/chromium/src/stacktrace_libunwind-inl.h
@@ -32,11 +32,6 @@
 //
 // Produce stack trace using libunwind
 
-#ifndef BASE_STACKTRACE_LIBINWIND_INL_H_
-#define BASE_STACKTRACE_LIBINWIND_INL_H_
-// Note: this file is included into stacktrace.cc more than once.
-// Anything that should only be defined once should be here:
-
 // We only need local unwinder.
 #define UNW_LOCAL_ONLY
 
@@ -57,30 +52,12 @@ extern "C" {
 // cases, we return 0 to indicate the situation.
 static __thread int recursive;
 
-#endif  // BASE_STACKTRACE_LIBINWIND_INL_H_
-
-// Note: this part of the file is included several times.
-// Do not put globals below.
-
-// The following 4 functions are generated from the code below:
-//   GetStack{Trace,Frames}()
-//   GetStack{Trace,Frames}WithContext()
-//
-// These functions take the following args:
-//   void** result: the stack-trace, as an array
-//   int* sizes: the size of each stack frame, as an array
-//               (GetStackFrames* only)
-//   int max_depth: the size of the result (and sizes) array(s)
-//   int skip_count: how many stack pointers to skip before storing in result
-//   void* ucp: a ucontext_t* (GetStack{Trace,Frames}WithContext only)
-int GET_STACK_TRACE_OR_FRAMES {
+// If you change this function, also change GetStackFrames below.
+int GetStackTrace(void** result, int max_depth, int skip_count) {
   void *ip;
   int n = 0;
   unw_cursor_t cursor;
   unw_context_t uc;
-#if IS_STACK_FRAMES
-  unw_word_t sp = 0, next_sp = 0;
-#endif
 
   if (recursive) {
     return 0;
@@ -90,39 +67,90 @@ int GET_STACK_TRACE_OR_FRAMES {
   unw_getcontext(&uc);
   int ret = unw_init_local(&cursor, &uc);
   assert(ret >= 0);
-  skip_count++;         // Do not include current frame
-
-  while (skip_count--) {
-    if (unw_step(&cursor) <= 0) {
-      goto out;
-    }
-#if IS_STACK_FRAMES
-    if (unw_get_reg(&cursor, UNW_REG_SP, &next_sp)) {
-      goto out;
-    }
-#endif
-  }
+  skip_count++;         // Do not include the "GetStackTrace" frame
 
   while (n < max_depth) {
     if (unw_get_reg(&cursor, UNW_REG_IP, (unw_word_t *) &ip) < 0) {
       break;
     }
-#if IS_STACK_FRAMES
-    sizes[n] = 0;
-#endif
-    result[n++] = ip;
+    if (skip_count > 0) {
+      skip_count--;
+    } else {
+      result[n++] = ip;
+    }
     if (unw_step(&cursor) <= 0) {
       break;
     }
-#if IS_STACK_FRAMES
+  }
+  --recursive;
+  return n;
+}
+
+// If you change this function, also change GetStackTrace above:
+//
+// This GetStackFrames routine shares a lot of code with GetStackTrace
+// above. This code could have been refactored into a common routine,
+// and then both GetStackTrace/GetStackFrames could call that routine.
+// There are two problems with that:
+//
+// (1) The performance of the refactored-code suffers substantially - the
+//     refactored needs to be able to record the stack trace when called
+//     from GetStackTrace, and both the stack trace and stack frame sizes,
+//     when called from GetStackFrames - this introduces enough new
+//     conditionals that GetStackTrace performance can degrade by as much
+//     as 50%.
+//
+// (2) Whether the refactored routine gets inlined into GetStackTrace and
+//     GetStackFrames depends on the compiler, and we can't guarantee the
+//     behavior either-way, even with "__attribute__ ((always_inline))"
+//     or "__attribute__ ((noinline))". But we need this guarantee or the
+//     frame counts may be off by one.
+//
+// Both (1) and (2) can be addressed without this code duplication, by
+// clever use of template functions, and by defining GetStackTrace and
+// GetStackFrames as macros that expand to these template functions.
+// However, this approach comes with its own set of problems - namely,
+// macros and  preprocessor trouble - for example,  if GetStackTrace
+// and/or GetStackFrames is ever defined as a member functions in some
+// class, we are in trouble.
+int GetStackFrames(void** pcs, int* sizes, int max_depth, int skip_count) {
+  void *ip;
+  int n = 0;
+  unw_cursor_t cursor;
+  unw_context_t uc;
+  unw_word_t sp = 0, next_sp = 0;
+
+  if (recursive) {
+    return 0;
+  }
+  ++recursive;
+
+  unw_getcontext(&uc);
+  RAW_CHECK(unw_init_local(&cursor, &uc) >= 0, "unw_init_local failed");
+  skip_count++;         // Do not include the "GetStackFrames" frame
+
+  while (skip_count--) {
+    if (unw_step(&cursor) <= 0 ||
+        unw_get_reg(&cursor, UNW_REG_SP, &next_sp) < 0) {
+      goto out;
+    }
+  }
+  while (n < max_depth) {
     sp = next_sp;
-    if (unw_get_reg(&cursor, UNW_REG_SP, &next_sp) , 0) {
+    if (unw_get_reg(&cursor, UNW_REG_IP, (unw_word_t *) &ip) < 0)
+      break;
+    if (unw_step(&cursor) <= 0 ||
+        unw_get_reg(&cursor, UNW_REG_SP, &next_sp)) {
+      // We couldn't step any further (possibly because we reached _start).
+      // Provide the last good PC we've got, and get out.
+      sizes[n] = 0;
+      pcs[n++] = ip;
       break;
     }
-    sizes[n - 1] = next_sp - sp;
-#endif
+    sizes[n] = next_sp - sp;
+    pcs[n++] = ip;
   }
-out:
+ out:
   --recursive;
   return n;
 }