Add better free tracking.

Included in this change:

- Change the tag when a pointer is freed so it's easy to detect if
  an already freed pointer is being used.
- Move the free backtrace out of the header. This backtrace is only
  used under only some circumstances, so no need to allocate space
  in all headers for it.
- Add new option free_track_backtrace_num_frames to specify how many
  frames to record when the free occurs. This removes the dependency
  on the backtrace option to get backtraces.

Bug: 26739265
Change-Id: I76f5209507dcf46af67ada162a7cb2bf282116f2

1 files changed, 1 insertions, 1 deletions

diff --git a/libc/malloc_debug/malloc_debug.h b/libc/malloc_debug/malloc_debug.h
index 4a15f77bf..cd025a786 100644
--- a/libc/malloc_debug/malloc_debug.h
+++ b/libc/malloc_debug/malloc_debug.h
@@ -39,7 +39,6 @@
 // will still be in this order.
 //   Header          (Required)
 //   BacktraceHeader (Optional: For the allocation backtrace)
-//   BacktraceHeader (Optional: For the free backtrace)
 //   uint8_t data    (Optional: Front guard, will be a multiple of sizeof(uintptr_t))
 //   allocation data
 //   uint8_t data    (Optional: End guard)
@@ -70,6 +69,7 @@ struct BacktraceHeader {
 } __attribute__((packed));
 
 constexpr uint32_t DEBUG_TAG = 0x1ee7d00d;
+constexpr uint32_t DEBUG_FREE_TAG = 0x1cc7dccd;
 constexpr char LOG_DIVIDER[] = "*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***";
 constexpr size_t FREE_TRACK_MEM_BUFFER_SIZE = 4096;