Keep shadow stacks to help heap checker unwind without frame pointers

third_party/tcmalloc/chromium/src/stacktrace_x86-inl.h

Index: third_party/tcmalloc/chromium/src/stacktrace_x86-inl.h
===================================================================
--- third_party/tcmalloc/chromium/src/stacktrace_x86-inl.h	(revision 57513)
+++ third_party/tcmalloc/chromium/src/stacktrace_x86-inl.h	(working copy)
@@ -65,6 +65,9 @@
 #endif
 
 #include "google/stacktrace.h"
+#if defined(KEEP_SHADOW_STACKS)
+#include "linux_shadow_stacks.h"
+#endif  // KEEP_SHADOW_STACKS
 
 #if defined(__linux__) && defined(__i386__) && defined(__ELF__) && defined(HAVE_MMAP)
 // Count "push %reg" instructions in VDSO __kernel_vsyscall(),
@@ -316,6 +319,21 @@
 #endif
 
   int n = 0;
+#if defined(KEEP_SHADOW_STACKS)
+  void **shadow_ip_stack;
+  void **shadow_sp_stack;
+  int stack_size;
+  shadow_ip_stack = (void**) get_shadow_ip_stack(&stack_size);
+  shadow_sp_stack = (void**) get_shadow_sp_stack(&stack_size);
+  int shadow_index = stack_size - 1;
+  for (int i = stack_size - 1; i >= 0; i--) {
+    if (sp == shadow_sp_stack[i]) {
+      shadow_index = i;
+      break;
+    }
+  }
+  void **prev_sp = NULL;
+#endif  // KEEP_SHADOW_STACKS
   while (sp && n < max_depth) {
     if (*(sp+1) == reinterpret_cast<void *>(0)) {
       // In 64-bit code, we often see a frame that
@@ -328,8 +346,17 @@
     void **next_sp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(sp, ucp);
     if (skip_count > 0) {
       skip_count--;
+#if defined(KEEP_SHADOW_STACKS)
+      shadow_index--;
+#endif  // KEEP_SHADOW_STACKS
     } else {
       result[n] = *(sp+1);
+#if defined(KEEP_SHADOW_STACKS)
+      if ((shadow_index > 0) && (sp == shadow_sp_stack[shadow_index])) {
+        shadow_index--;
+      }
+#endif  // KEEP_SHADOW_STACKS
+
 #if IS_STACK_FRAMES
       if (next_sp > sp) {
         sizes[n] = (uintptr_t)next_sp - (uintptr_t)sp;
@@ -340,7 +367,25 @@
 #endif
       n++;
     }
+#if defined(KEEP_SHADOW_STACKS)
+    prev_sp = sp;
+#endif  // KEEP_SHADOW_STACKS
     sp = next_sp;
   }
+
+#if defined(KEEP_SHADOW_STACKS)
+  if (shadow_index >= 0) {
+    for (int i = shadow_index; i >= 0; i--) {
+      if (shadow_sp_stack[i] > prev_sp) {
+        result[n] = shadow_ip_stack[i];
+        if (n + 1 < max_depth) {
+          n++;
+          continue;
+        }
+      }
+      break;
+    }
+  }
+#endif  // KEEP_SHADOW_STACKS
   return n;
 }