[LTP] [PATCH v2 1/1] overcommit_memory: Disable optimization for malloc to prevent false positives

[Jan Stancek]

On Thu, May 22, 2025 at 5:21 PM Jan Polensky <japo@linux.ibm.com> wrote:
>
> When compiling with GCC 15.1.1+, the default-enabled -fmalloc-dce=2 and
> -fallocation-dce under -O2 can eliminate the entire malloc block because its
> result is only compared to NULL and/or passed to free().
>
> This leads to false positives in tests that expect malloc() to fail under memory
> pressure, as the allocation is optimized away.
>
> Disable this optimization for the affected function to preserve the intended
> test behavior.
>
> References: https://gcc.gnu.org/onlinedocs/gcc-15.1.0/gcc/Optimize-Options.html
> Signed-off-by: Jan Polensky <japo@linux.ibm.com>

Pushed.

Thanks,
Jan

> ---
> Changes since v1 (thanks to Cyril Hrubis):
> - Use LTP_VAR_USED macro to prevent GCC from optimizing away malloc().
>
>  testcases/kernel/mem/tunable/overcommit_memory.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/testcases/kernel/mem/tunable/overcommit_memory.c b/testcases/kernel/mem/tunable/overcommit_memory.c
> index b5beebbcd3c4..9b2cb479d5ee 100644
> --- a/testcases/kernel/mem/tunable/overcommit_memory.c
> +++ b/testcases/kernel/mem/tunable/overcommit_memory.c
> @@ -62,6 +62,7 @@
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <limits.h>
> +#include "tst_common.h"
>  #include "tst_test.h"
>
>  #define DEFAULT_OVER_RATIO     50L
> @@ -155,7 +156,7 @@ static int heavy_malloc(long size)
>  {
>         char *p;
>
> -       p = malloc(size * TST_KB);
> +       LTP_VAR_USED(p) = malloc(size * TST_KB);
>         if (p != NULL) {
>                 tst_res(TINFO, "malloc %ld kB successfully", size);
>                 free(p);
> --
> 2.49.0
>
>
> --
> Mailing list info: https://lists.linux.it/listinfo/ltp
>