[LTP] [RFC PATCH v1 1/1] overcommit_memory: Disable optimization for malloc to prevent false positives

[LTP] [RFC PATCH v1 1/1] overcommit_memory: Disable optimization for malloc to prevent false positives

[Jan Polensky]

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>
---
 testcases/kernel/mem/tunable/overcommit_memory.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/testcases/kernel/mem/tunable/overcommit_memory.c b/testcases/kernel/mem/tunable/overcommit_memory.c
index b5beebbcd3c4..fb42dbb75a00 100644
--- a/testcases/kernel/mem/tunable/overcommit_memory.c
+++ b/testcases/kernel/mem/tunable/overcommit_memory.c
@@ -151,6 +151,7 @@ static void overcommit_memory_test(void)

 }

+__attribute__((optimize("O0")))
 static int heavy_malloc(long size)
 {
 	char *p;
--
2.49.0


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Re: [LTP] [RFC PATCH v1 1/1] overcommit_memory: Disable optimization for malloc to prevent false positives

[Cyril Hrubis]

Hi!
We already have a macro for this usecase introduced in the commit:

commit 5bb0c6bc553a3393627b371275b2e34b0099de19
Author: Jan Stancek <jstancek@redhat.com>
Date:   Thu Feb 6 10:42:31 2025 +0100

    syscalls/mallinfo02: introduce LTP_VAR_USED to avoid optimization


Can you please use the LTP_VAR_USED() instead?

-- 
Cyril Hrubis
chrubis@suse.cz

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