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

[Jan Stancek]

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.

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
+
 #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