The patch titled Subject: lib: stackinit: hide never-taken branch from compiler has been added to the -mm mm-hotfixes-unstable branch. Its filename is lib-stackinit-hide-never-taken-branch-from-compiler.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Kees Cook kees@kernel.org Subject: lib: stackinit: hide never-taken branch from compiler Date: Sun, 17 Nov 2024 03:38:13 -0800

The never-taken branch leads to an invalid bounds condition, which is by design. To avoid the unwanted warning from the compiler, hide the variable from the optimizer.

../lib/stackinit_kunit.c: In function 'do_nothing_u16_zero': ../lib/stackinit_kunit.c:51:49: error: array subscript 1 is outside array bounds of 'u16[0]' {aka 'short unsigned int[]'} [-Werror=array-bounds=] 51 | #define DO_NOTHING_RETURN_SCALAR(ptr) *(ptr) | ^~~~~~ ../lib/stackinit_kunit.c:219:24: note: in expansion of macro 'DO_NOTHING_RETURN_SCALAR' 219 | return DO_NOTHING_RETURN_ ## which(ptr + 1); \ | ^~~~~~~~~~~~~~~~~~

Link: https://lkml.kernel.org/r/20241117113813.work.735-kees@kernel.org Signed-off-by: Kees Cook kees@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

lib/stackinit_kunit.c | 1 + 1 file changed, 1 insertion(+)

--- a/lib/stackinit_kunit.c~lib-stackinit-hide-never-taken-branch-from-compiler +++ a/lib/stackinit_kunit.c @@ -212,6 +212,7 @@ static noinline void test_ ## name (stru static noinline DO_NOTHING_TYPE_ ## which(var_type) \ do_nothing_ ## name(var_type *ptr) \ { \ + OPTIMIZER_HIDE_VAR(ptr); \ /* Will always be true, but compiler doesn't know. */ \ if ((unsigned long)ptr > 0x2) \ return DO_NOTHING_RETURN_ ## which(ptr); \ _

Patches currently in -mm which might be from kees@kernel.org are

lib-stackinit-hide-never-taken-branch-from-compiler.patch