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mtrace: Deprecate mallwatch and tr_break

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The variable and function pair appear to provide a way for users to
set conditional breakpoints in mtrace when a specific address is
returned by the allocator.  This can be achieved by using conditional
breakpoints in gdb so it is redundant.  There is no documentation of
this interface in the manual either, so it appears to have been a hack
that got added to debug malloc.  Deprecate these symbols and do not
call tr_break anymore.

Reviewed-by: DJ Delorie <dj@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Siddhesh Poyarekar 2021-07-03 00:47:34 +05:30
parent 7df5c7bcce
commit 00d28960c5
2 changed files with 24 additions and 37 deletions
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4
NEWS
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@ -93,6 +93,10 @@ Deprecated and removed features, and other changes affecting compatibility:
package managers that delete removed files late during the package
upgrade or downgrade process.
* The symbols mallwatch and tr_break are now deprecated and no longer used in
mtrace. Similar functionality can be achieved by using conditional
breakpoints within mtrace functions from within gdb.
Changes to build and runtime requirements:
* On Linux, the shm_open, sem_open, and related functions now expect the

57
malloc/mtrace.c
View File

@ -50,8 +50,25 @@ static char *malloc_trace_buffer;
__libc_lock_define_initialized (static, lock);
/* Address to breakpoint on accesses to... */
#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_34)
/* Compatibility symbols that were introduced to help break at allocation sites
for specific memory allocations. This is unusable with ASLR, although gdb
may allow predictable allocation addresses. Even then, gdb has watchpoint
and conditional breakpoint support which should provide the same
functionality without having this kludge. These symbols are preserved in
case some applications ended up linking against them but they don't actually
do anything anymore; not that they did much before anyway. */
void *mallwatch;
compat_symbol (libc, mallwatch, mallwatch, GLIBC_2_0);
void
tr_break (void)
{
}
compat_symbol (libc, tr_break, tr_break, GLIBC_2_0);
#endif
/* Old hook values. */
static void (*tr_old_free_hook) (void *ptr, const void *);
@ -61,19 +78,6 @@ static void *(*tr_old_realloc_hook) (void *ptr, size_t size,
static void *(*tr_old_memalign_hook) (size_t __alignment, size_t __size,
const void *);
/* This function is called when the block being alloc'd, realloc'd, or
freed has an address matching the variable "mallwatch". In a debugger,
set "mallwatch" to the address of interest, then put a breakpoint on
tr_break. */
extern void tr_break (void) __THROW;
libc_hidden_proto (tr_break)
void
tr_break (void)
{
}
libc_hidden_def (tr_break)
static void
tr_where (const void *caller, Dl_info *info)
{
@ -167,12 +171,6 @@ tr_freehook (void *ptr, const void *caller)
tr_where (caller, info);
/* Be sure to print it first. */
fprintf (mallstream, "- %p\n", ptr);
if (ptr == mallwatch)
{
__libc_lock_unlock (lock);
tr_break ();
__libc_lock_lock (lock);
}
set_default_hooks ();
if (tr_old_free_hook != NULL)
(*tr_old_free_hook)(ptr, caller);
@ -203,9 +201,6 @@ tr_mallochook (size_t size, const void *caller)
__libc_lock_unlock (lock);
if (hdr == mallwatch)
tr_break ();
return hdr;
}
@ -214,9 +209,6 @@ tr_reallochook (void *ptr, size_t size, const void *caller)
{
void *hdr;
if (ptr == mallwatch)
tr_break ();
Dl_info mem;
Dl_info *info = lock_and_info (caller, &mem);
@ -247,9 +239,6 @@ tr_reallochook (void *ptr, size_t size, const void *caller)
__libc_lock_unlock (lock);
if (hdr == mallwatch)
tr_break ();
return hdr;
}
@ -274,9 +263,6 @@ tr_memalignhook (size_t alignment, size_t size, const void *caller)
__libc_lock_unlock (lock);
if (hdr == mallwatch)
tr_break ();
return hdr;
}
@ -296,10 +282,7 @@ release_libc_mem (void)
#endif
/* We enable tracing if either the environment variable MALLOC_TRACE
is set, or if the variable mallwatch has been patched to an address
that the debugging user wants us to stop on. When patching mallwatch,
don't forget to set a breakpoint on tr_break! */
/* We enable tracing if the environment variable MALLOC_TRACE is set. */
void
mtrace (void)
@ -321,7 +304,7 @@ mtrace (void)
#else
mallfile = getenv (mallenv);
#endif
if (mallfile != NULL || mallwatch != NULL)
if (mallfile != NULL)
{
char *mtb = malloc (TRACE_BUFFER_SIZE);
if (mtb == NULL)