malloc: Use mtag_enabled instead of USE_MTAG

Use the runtime check where possible: it should not cause slow down in
the !USE_MTAG case since then mtag_enabled is constant false, but it
allows compiling the tagging logic so it's less likely to break or
diverge when developers only test the !USE_MTAG case.

Reviewed-by: DJ Delorie <dj@redhat.com>

2 files changed, 8 insertions, 12 deletions

diff --git a/malloc/hooks.c b/malloc/hooks.c
index d8e304c31c..9474e199c3 100644
--- a/malloc/hooks.c
+++ b/malloc/hooks.c
@@ -262,11 +262,10 @@ free_check (void *mem, const void *caller)
 
   int err = errno;
 
-#ifdef USE_MTAG
   /* Quickly check that the freed pointer matches the tag for the memory.
      This gives a useful double-free detection.  */
-  *(volatile char *)mem;
-#endif
+  if (__glibc_unlikely (mtag_enabled))
+    *(volatile char *)mem;
 
   __libc_lock_lock (main_arena.mutex);
   p = mem2chunk_check (mem, NULL);
@@ -310,11 +309,10 @@ realloc_check (void *oldmem, size_t bytes, const void *caller)
       return NULL;
     }
 
-#ifdef USE_MTAG
   /* Quickly check that the freed pointer matches the tag for the memory.
      This gives a useful double-free detection.  */
-  *(volatile char *)oldmem;
-#endif
+  if (__glibc_unlikely (mtag_enabled))
+    *(volatile char *)oldmem;
 
   __libc_lock_lock (main_arena.mutex);
   const mchunkptr oldp = mem2chunk_check (oldmem, &magic_p);
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 849bd8e2c9..36583120ce 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3286,11 +3286,10 @@ __libc_free (void *mem)
   if (mem == 0)                              /* free(0) has no effect */
     return;
 
-#ifdef USE_MTAG
   /* Quickly check that the freed pointer matches the tag for the memory.
      This gives a useful double-free detection.  */
-  *(volatile char *)mem;
-#endif
+  if (__glibc_unlikely (mtag_enabled))
+    *(volatile char *)mem;
 
   int err = errno;
 
@@ -3352,11 +3351,10 @@ __libc_realloc (void *oldmem, size_t bytes)
   if (oldmem == 0)
     return __libc_malloc (bytes);
 
-#ifdef USE_MTAG
   /* Perform a quick check to ensure that the pointer's tag matches the
      memory's tag.  */
-  *(volatile char*) oldmem;
-#endif
+  if (__glibc_unlikely (mtag_enabled))
+    *(volatile char*) oldmem;
 
   /* chunk corresponding to oldmem */
   const mchunkptr oldp = mem2chunk (oldmem);