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Subject[PATCH] ELF: add and use SUPRESS_WARN_UNUSED_RESULT
Last write to the "error" variable in load_elf_binary() is dead write.

Add and use SUPRESS_WARN_UNUSED_RESULT macro to express intent better.

Credit goes to Ed Catmur:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66425#c34

Macro doesn't work for WUR functions returning structures and unions,
but it will work once gcc copies clang.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

fs/binfmt_elf.c | 3 ++-
include/linux/compiler_attributes.h | 4 ++++
2 files changed, 6 insertions(+), 1 deletion(-)

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1290,7 +1290,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
and some applications "depend" upon this behavior.
Since we do not have the power to recompile these, we
emulate the SVr4 behavior. Sigh. */
- error = vm_mmap(NULL, 0, PAGE_SIZE, PROT_READ | PROT_EXEC,
+ SUPRESS_WARN_UNUSED_RESULT
+ vm_mmap(NULL, 0, PAGE_SIZE, PROT_READ | PROT_EXEC,
MAP_FIXED | MAP_PRIVATE, 0);
}

--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -284,6 +284,10 @@
* clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
*/
#define __must_check __attribute__((__warn_unused_result__))
+/*
+ * "(void)" is enough for clang but not for gcc.
+ */
+#define SUPRESS_WARN_UNUSED_RESULT (void)!

/*
* gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
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