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/lib-stackinit-hide-never-taken-branch-from-compiler.patch
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@xxxxxxxxxx>
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@xxxxxxxxxx
Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx are
lib-stackinit-hide-never-taken-branch-from-compiler.patch
