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dri: Fix "cosmetic" undefined behaviour warning for RGB[A]16_UNORM formats.

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Ian Romanick reported some "undefined behaviour" warnings during some
not specified tests, relating to introduction of RGB[A}16_UNORM formats
in merge request
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38588

This due to overflowing the 32-bits masks[], and then during assignment
the red/green/blue/alphaMask fields in struct gl_config when using a 16
bpc format. Iow. the red/green/blue/alphaMask would not be usable.

Suppress this warning by setting masks[] to zero for unorm16 formats,
just as was previously done for is_float16, ie. fp16 formats.

16 bpc formats are only exposed for display on non-X11 WSI target
platforms like GBM+DRM, Wayland, surfaceless, and these platforms do
not use the info in red/green/blue/alphaMask at all, so the "undefined
behaviour" is meaningless.

Fixes: f2aaa9ce00 ("dri,gallium: Add support for RGB[A]16_UNORM display formats.")
Reported-by: Ian Romanick @idr
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
(cherry picked from commit ab94515b0a)

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40752>
This commit is contained in:
Mario Kleiner 2026-03-29 19:21:15 +02:00 • committed by Eric Engestrom
parent 58ab5760c1
commit af53a9bfbc
2 changed files with 8 additions and 2 deletions
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2
.pick_status.json
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@ -74,7 +74,7 @@
"description": "dri: Fix \"cosmetic\" undefined behaviour warning for RGB[A]16_UNORM formats.",
"nominated": true,
"nomination_type": 2,
"resolution": 0,
"resolution": 1,
"main_sha": null,
"because_sha": "f2aaa9ce00ffe7310bddcd5e884f34afb741f460",
"notes": null

8
src/gallium/frontends/dri/dri_screen.c
View file

@ -153,9 +153,11 @@ driCreateConfigs(enum pipe_format format,
unsigned num_accum_bits = (enable_accum) ? 2 : 1;
bool is_srgb;
bool is_float;
bool is_unorm16;
is_srgb = util_format_is_srgb(format);
is_float = util_format_is_float(format);
is_unorm16 = util_format_is_unorm16(util_format_description(format));
for (i = 0; i < 4; i++) {
color_bits[i] =
@ -168,7 +170,11 @@ driCreateConfigs(enum pipe_format format,
shifts[i] = -1;
}
if (is_float || color_bits[i] == 0)
/* is_float and is_unorm16 is only true on non-x11 target platforms, which
* don't actually use redMask, greenMask, ..., so avoid setting masks[]
* to prevent a meaningless "undefined behaviour" build warning.
*/
if (is_float || is_unorm16 || color_bits[i] == 0)
masks[i] = 0;
else
masks[i] = ((1u << color_bits[i]) - 1) << shifts[i];