Re: [LTP] [PATCH] syscalls/mallinfo02: introduce LTP_VAR_USED to avoid optimization

[Cyril Hrubis <chrubis@suse.cz>]

Hi!
> gcc 15 is a bit more clever and noticed that 'buf' isn't used
> for anything so it optimized it out, including call to malloc.
> So, there's also no mmap() call behind it and test fails,
> because nothing was allocated.

Huh, that sounds like the optimizations are getting more and more evil
over the time.

> Introduce LTP_VAR_USED macro, that makes compiler aware of the
> variable and doesn't optimize it out.
> 
> Signed-off-by: Jan Stancek <jstancek@redhat.com>
> ---
>  include/tst_common.h                               | 2 ++
>  testcases/kernel/syscalls/mallinfo2/mallinfo2_01.c | 2 +-
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/tst_common.h b/include/tst_common.h
> index b14bbae04077..3de826acd0ec 100644
> --- a/include/tst_common.h
> +++ b/include/tst_common.h
> @@ -13,6 +13,8 @@
>  #define LTP_ATTRIBUTE_UNUSED		__attribute__((unused))
>  #define LTP_ATTRIBUTE_UNUSED_RESULT	__attribute__((warn_unused_result))
>  
> +#define LTP_VAR_USED(p) asm volatile("" :: "m"(p)); p

Shouldn't __attribute__((used)) suffice?

>  #ifndef ARRAY_SIZE
>  # define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
>  #endif
> diff --git a/testcases/kernel/syscalls/mallinfo2/mallinfo2_01.c b/testcases/kernel/syscalls/mallinfo2/mallinfo2_01.c
> index 90cf4fcb3b89..51783fc22b80 100644
> --- a/testcases/kernel/syscalls/mallinfo2/mallinfo2_01.c
> +++ b/testcases/kernel/syscalls/mallinfo2/mallinfo2_01.c
> @@ -26,7 +26,7 @@ void test_mallinfo2(void)
>  	char *buf;
>  	size_t size = 2UL * 1024UL * 1024UL * 1024UL;
>  
> -	buf = malloc(size);
> +	LTP_VAR_USED(buf) = malloc(size);
>  
>  	if (!buf)
>  		tst_brk(TCONF, "Current system can not malloc 2G space, skip it");
> -- 
> 2.43.0
> 
> 
> -- 
> Mailing list info: https://lists.linux.it/listinfo/ltp

-- 
Cyril Hrubis
chrubis@suse.cz

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp