[PATCH] [RFC] ubsan: disallow bounds checking with gcov on broken gcc

[Arnd Bergmann]

From: Arnd Bergmann <arnd@xxxxxxxx>

Combining UBSAN and GCOV in randconfig builds results in a number of
stack frame size warnings, such as:

crypto/twofish_common.c:683:1: error: the frame size of 2040 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
drivers/media/platform/mediatek/vcodec/vdec/vdec_vp9_req_lat_if.c:1589:1: error: the frame size of 1696 bytes is larger than 1400 bytes [-Werror=frame-larger-than=]
drivers/media/platform/verisilicon/hantro_g2_vp9_dec.c:754:1: error: the frame size of 1260 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
drivers/staging/media/ipu3/ipu3-css-params.c:1206:1: error: the frame size of 1080 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
drivers/staging/media/rkvdec/rkvdec-vp9.c:1042:1: error: the frame size of 2176 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
drivers/staging/media/rkvdec/rkvdec-vp9.c:995:1: error: the frame size of 1656 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]

I managed to track this down to the -fsanitize=bounds option clashing
with the -fprofile-arcs option, which leads a lot of spilled temporary
variables in generated instrumentation code.

Hopefully this can be addressed in future gcc releases the same way
that clang handles the combination, but for existing compiler releases,
it seems best to disable one of the two flags. This can be done either
globally by just not passing both at the same time, or locally using
the no_sanitize or no_instrument_function attributes in the affected
functions.

Try the simplest approach here, and turn off -fsanitize=bounds on
gcc when GCOV is enabled, leaving the rest of UBSAN working. Doing
this globally also helps avoid inefficient code from the same
problem that did not push the build over the warning limit.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Link: https://lore.kernel.org/stable/6b1a0ee6-c78b-4873-bfd5-89798fce9899@kili.mountain/
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110074
Link: https://godbolt.org/z/zvf7YqK5K
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 lib/Kconfig.ubsan | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index f7cbbad2bb2f4..8f71ff8f27576 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -29,6 +29,8 @@ config UBSAN_TRAP
 
 config CC_HAS_UBSAN_BOUNDS_STRICT
 	def_bool $(cc-option,-fsanitize=bounds-strict)
+	# work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110074
+	depends on GCC_VERSION > 140000 || !GCOV_PROFILE_ALL
 	help
 	  The -fsanitize=bounds-strict option is only available on GCC,
 	  but uses the more strict handling of arrays that includes knowledge
-- 
2.39.2