[PATCH] media: mediatek: vcodec: mark vdec_vp9_slice_map_counts_eob_coef noinline

Arnd Bergmann
2024-10-18T15:16:47Z

From: Arnd Bergmann <arnd@arndb.de>

With KASAN enabled, clang fails to optimize the inline version of
vdec_vp9_slice_map_counts_eob_coef() properly, leading to kilobytes
of temporary values spilled to the stack:

drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c:1526:12: error: stack frame size (2160) exceeds limit (2048) in 'vdec_vp9_slice_update_prob' [-Werror,-Wframe-larger-than]

This seems to affect all versions of clang including the latest (clang-20),
but the degree of stack overhead is different per release.

Marking the function as noinline_for_stack is harmless here and avoids
the problem completely.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
I have not come to a conclusion on how exactly clang fails to do this
right, but can provide the .config and/or preprocessed source files
and command line if we think this should be fixed in clang.
---
.../mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c b/drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c
index eea709d93820..47c302745c1d 100644
--- a/drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c
+++ b/drivers/media/platform/mediatek/vcodec/decoder/vdec/vdec_vp9_req_lat_if.c
@@ -1188,7 +1188,8 @@ static int vdec_vp9_slice_setup_lat(struct vdec_vp9_slice_instance *instance,
return ret;
}

-static
+/* clang stack usage explodes if this is inlined */
+static noinline_for_stack
void vdec_vp9_slice_map_counts_eob_coef(unsigned int i, unsigned int j, unsigned int k,
struct vdec_vp9_slice_frame_counts *counts,
struct v4l2_vp9_frame_symbol_counts *counts_helper)
--
2.39.5