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work around constant folding bug 61144 in gcc 4.9.0 and 4.9.1

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previously we detected this bug in configure and issued advice for a
workaround, but this turned out not to work. since then gcc 4.9.0 has
appeared in several distributions, and now 4.9.1 has been released
without a fix despite this being a wrong code generation bug which is
supposed to be a release-blocker, per gcc policy.

since the scope of the bug seems to affect only data objects (rather
than functions) whose definitions are overridable, and there are only
a very small number of these in musl, I am just changing them from
const to volatile for the time being. simply removing the const would
be sufficient to make gcc 4.9.1 work (the non-const case was
inadvertently fixed as part of another change in gcc), and this would
also be sufficient with 4.9.0 if we forced -O0 on the affected files
or on the whole build. however it's cleaner to just remove all the
broken compiler detection and use volatile, which will ensure that
they are never constant-folded. the quality of a non-broken compiler's
output should not be affected except for the fact that these objects
are no longer const and thus possibly add a few bytes to data/bss.

this change can be reconsidered and possibly reverted at some point in
the future when the broken gcc versions are no longer relevant.
This commit is contained in:
Rich Felker 2014-07-16 21:32:06 -04:00
commit a6adb2bcd8
8 changed files with 9 additions and 30 deletions
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6
src/thread/pthread_create.c
View file

@ -116,12 +116,12 @@ static int start(void *p)
#define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE)
/* pthread_key_create.c overrides this */
static const size_t dummy = 0;
static volatile size_t dummy = 0;
weak_alias(dummy, __pthread_tsd_size);
static void *const dummy_tsd[1] = { 0 };
static void *dummy_tsd[1] = { 0 };
weak_alias(dummy_tsd, __pthread_tsd_main);
static FILE *const dummy_file = 0;
static FILE *volatile dummy_file = 0;
weak_alias(dummy_file, __stdin_used);
weak_alias(dummy_file, __stdout_used);
weak_alias(dummy_file, __stderr_used);

2
src/thread/pthread_key_create.c
View file

@ -1,6 +1,6 @@
#include "pthread_impl.h"
const size_t __pthread_tsd_size = sizeof(void *) * PTHREAD_KEYS_MAX;
volatile size_t __pthread_tsd_size = sizeof(void *) * PTHREAD_KEYS_MAX;
void *__pthread_tsd_main[PTHREAD_KEYS_MAX] = { 0 };
static void (*keys[PTHREAD_KEYS_MAX])(void *);