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malloc: Use mtag_enabled instead of USE_MTAG

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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>
This commit is contained in:
Szabolcs Nagy
2021-02-17 10:15:18 +00:00
parent 63a20eb03c
commit d32624802d
2 changed files with 8 additions and 12 deletions
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6
malloc/hooks.c
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@ -262,11 +262,10 @@ free_check (void *mem, const void *caller)
int err = errno; int err = errno;
#ifdef USE_MTAG
/* Quickly check that the freed pointer matches the tag for the memory. /* Quickly check that the freed pointer matches the tag for the memory.
This gives a useful double-free detection. */ This gives a useful double-free detection. */
if (__glibc_unlikely (mtag_enabled))
*(volatile char *)mem; *(volatile char *)mem;
#endif
__libc_lock_lock (main_arena.mutex); __libc_lock_lock (main_arena.mutex);
p = mem2chunk_check (mem, NULL); p = mem2chunk_check (mem, NULL);
@ -310,11 +309,10 @@ realloc_check (void *oldmem, size_t bytes, const void *caller)
return NULL; return NULL;
} }
#ifdef USE_MTAG
/* Quickly check that the freed pointer matches the tag for the memory. /* Quickly check that the freed pointer matches the tag for the memory.
This gives a useful double-free detection. */ This gives a useful double-free detection. */
if (__glibc_unlikely (mtag_enabled))
*(volatile char *)oldmem; *(volatile char *)oldmem;
#endif
__libc_lock_lock (main_arena.mutex); __libc_lock_lock (main_arena.mutex);
const mchunkptr oldp = mem2chunk_check (oldmem, &magic_p); const mchunkptr oldp = mem2chunk_check (oldmem, &magic_p);

6
malloc/malloc.c
View File

@ -3286,11 +3286,10 @@ __libc_free (void *mem)
if (mem == 0) /* free(0) has no effect */ if (mem == 0) /* free(0) has no effect */
return; return;
#ifdef USE_MTAG
/* Quickly check that the freed pointer matches the tag for the memory. /* Quickly check that the freed pointer matches the tag for the memory.
This gives a useful double-free detection. */ This gives a useful double-free detection. */
if (__glibc_unlikely (mtag_enabled))
*(volatile char *)mem; *(volatile char *)mem;
#endif
int err = errno; int err = errno;
@ -3352,11 +3351,10 @@ __libc_realloc (void *oldmem, size_t bytes)
if (oldmem == 0) if (oldmem == 0)
return __libc_malloc (bytes); return __libc_malloc (bytes);
#ifdef USE_MTAG
/* Perform a quick check to ensure that the pointer's tag matches the /* Perform a quick check to ensure that the pointer's tag matches the
memory's tag. */ memory's tag. */
if (__glibc_unlikely (mtag_enabled))
*(volatile char*) oldmem; *(volatile char*) oldmem;
#endif
/* chunk corresponding to oldmem */ /* chunk corresponding to oldmem */
const mchunkptr oldp = mem2chunk (oldmem); const mchunkptr oldp = mem2chunk (oldmem);