[Mac] Remove potential for malloc in CrMallocErrorBreak().

base/process_util_mac.mm

Index: base/process_util_mac.mm
diff --git a/base/process_util_mac.mm b/base/process_util_mac.mm
index 1fa3dbbb4067145c4038a63ab3c25ab0c22be9db..318f8d05408e9a168aaaf3f093af21af90b851cb 100644
--- a/base/process_util_mac.mm
+++ b/base/process_util_mac.mm
@@ -590,6 +590,8 @@ class ThreadLocalBooleanAutoReset {
 base::LazyInstance<ThreadLocalBoolean>::Leaky
     g_unchecked_malloc = LAZY_INSTANCE_INITIALIZER;
 
+// NOTE(shess): This is called when the malloc library noticed that the heap
+// is fubar.  Avoid calls which will re-enter the malloc library.
 void CrMallocErrorBreak() {
   g_original_malloc_error_break();
 
@@ -602,8 +604,17 @@ void CrMallocErrorBreak() {
     return;
 
   // A unit test checks this error message, so it needs to be in release builds.
-  PLOG(ERROR) <<
-      "Terminating process due to a potential for future heap corruption";
+  char buf[1024] =
+      "Terminating process due to a potential for future heap corruption: "
+      "errno==";

[Mark Mentovai, 2012/11/12 23:19:32]

One = too many?

[Scott Hess - ex-Googler, 2012/11/12 23:39:53]

Done.  I was thinking C-style is-equal-to, but a byte is a byte.

+  char errnobuf[4] = {

[Mark Mentovai, 2012/11/12 23:19:32]

No [4], just [].

[Scott Hess - ex-Googler, 2012/11/12 23:39:53]

Done.

+    '0' + ((errno / 100) % 10),
+    '0' + ((errno / 10) % 10),
+    '0' + (errno % 10),
+    '\000'
+  };

[Mark Mentovai, 2012/11/12 23:19:32]

Ha!

Do you want to COMPILE_ASSERT that ELAST <= 999?

[Scott Hess - ex-Googler, 2012/11/12 23:39:53]

Honestly, I kind of questioned even the third digit.  But, sure.

+  strlcat(buf, errnobuf, sizeof(buf));

[Mark Mentovai, 2012/11/12 23:19:32]

I can think of a way to avoid the copy, but that’s just for fun at that point,
there’s nothing wrong with the strlcat.

[Scott Hess - ex-Googler, 2012/11/12 23:39:53]

There are dozens of ways to skin this cat, and they're all guaranteed to be
gross.

+  RAW_LOG(ERROR, buf);
 
   // Crash by writing to NULL+errno to allow analyzing errno from
   // crash dump info (setting a breakpad key would re-enter the malloc
@@ -629,6 +640,10 @@ void EnableTerminationOnHeapCorruption() {
     return;
   }
 
+  // Warm this up so that it doesn't require allocation when
+  // |CrMallocErrorBreak()| calls it.
+  ignore_result(g_unchecked_malloc.Get().Get());
+
   mach_error_t err = mach_override_ptr(
      (void*)malloc_error_break,
      (void*)&CrMallocErrorBreak,