Avoid compiler optimisation of malloc calls
PATCH 1/1 Avoid compiler optimisation of malloc calls
clang understands the malloc library call and can optimise calls to it. In particular it will avoid calling malloc completely if it detects that the result is not used.
--- .../conformance/interfaces/pthread_cond_init/4-1.c | 19 ++++++++++++------- 1 files changed, 12 insertions(+), 7 deletions(-)
(quoted diff) +0 -0
a/testcases/open_posix_testsuite/conformance/interfaces/pthread_cond_init/4-1.c b/testcases/open_posix_testsuite/conformance/interfaces/pthread_cond_init/4-1.c index 287fda1..7932ec2 100644
---
a/testcases/open_posix_testsuite/conformance/interfaces/pthread_cond_init/4-1.c
+++
b/testcases/open_posix_testsuite/conformance/interfaces/pthread_cond_init/4-1.c @@ -50,7 +50,7 @@
#define ERR_MSG(f, rc) printf("Failed: func: %s rc: %s (%u)\n", \
f, strerror(rc), rc);
-/* Max memory for child is 81B */
+/* Max memory for child is 1MB */
#define MAX_MEM ((1<<20))
/*
@@ -59,8 +59,8 @@
*/
static void child(void)
{
- char *curr;
- char *prev = NULL;
+ void *curr;
+ void *prev = NULL;
struct rlimit rl;
pthread_cond_t cond;
pthread_condattr_t attr;
@@ -76,10 +76,15 @@ static void child(void)
exit(PTS_UNRESOLVED);
}
- /* Consume all memory we can */
- do {
- curr = malloc(1);
- } while (curr);
+ /*
+ * Consume all memory we can
+ * It's important to use the malloc() return value in a
+ * meaningful way to bypass potential compiler optimisations.
+ */
+ while ((curr = malloc(sizeof(void *)))) {
+ *(void **)curr = prev;
+ prev = curr;
+ }
if (errno != ENOMEM) {
ERR_MSG("malloc()", errno);
exit(PTS_UNRESOLVED);
Signature · 13 lines
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Hi!
Quoted 3 lines
clang understands the malloc library call and can optimise calls to it. In particular it will avoid calling malloc completely if it detects that the result is not used.
Both patches are okay, but seems to be corrupted (git am wasn't able to understand them).
Could you send these again (possibly with git send-email) or send a pull request from repo forked on github or anything else that would work?
Signature · 12 lines
Cyril Hrubis [email protected] ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_sfd2d_oct _______________________________________________ Ltp-list mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/ltp-list
PATCH 1/1 Avoid compiler optimisation of malloc calls
In reply to Chris Dearmanclang understands the malloc library call and can optimise calls to it. In particular it will avoid calling malloc completely if it detects that the result is not used.
--- .../conformance/interfaces/pthread_cond_init/4-1.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-)
testcases/open_posix_testsuite/conformance/interfaces/pthread_cond_init/4-1.c +12 -7
@@ -50,7 +50,7 @@#define ERR_MSG (f, rc) printf("Failed: func: %s rc: %s (%u)\n", \ f, strerror(rc), rc); -/* Max memory for child is 81B */ +/* Max memory for child is 1MB */ #define MAX_MEM ((1<<20))/*
@@ -59,8 +59,8 @@*/ static void child (void ) { -char *curr; -char *prev =NULL ; +void *curr; +void *prev =NULL ;struct rlimit rl;pthread_cond_t cond;pthread_condattr_t attr;
@@ -76,10 +76,15 @@ static void child(void)exit (PTS_UNRESOLVED ); } -/* Consume all memory we can */ -do { - curr =malloc (1 ); - }while (curr); +/* +* Consume all memory we can +* It's importamt to use the malloc() return value in a +* meaningful way to bypass potential compiler optimisations. +*/ +while ((curr =malloc (sizeof (void *)))) { + *(void **)curr = prev; + prev = curr; + }if (errno !=ENOMEM ) {ERR_MSG ("malloc()" , errno);exit (PTS_UNRESOLVED );
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Quoted 5 lines · Chris Dearman
clang understands the malloc library call and can optimise calls to it. In particular it will avoid calling malloc completely if it detects that the result is not used.
Signed-off-by Chris Dearman <[email protected]>
Pushed with Cyril's Ack, thank you.
Wanlong Gao
Quoted 14 lines
--- .../conformance/interfaces/pthread_cond_init/4-1.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-)------------------------------------------------------------------------------
Everyone hates slow websites. So do we.
Make your web apps faster with AppDynamics
Download AppDynamics Lite for free today:
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Quoted 5 lines
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------------------------------------------------------------------------------
Everyone hates slow websites. So do we.
Make your web apps faster with AppDynamics
Download AppDynamics Lite for free today:
http://p.sf.net/sfu/appdyn_sfd2d_oct
_______________________________________________
Ltp-list mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/ltp-list