From e5f7e4e0a445f1b9b81ddc9b968e52b44f9d4242 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 21 Apr 2025 14:58:34 -0700 Subject: [PATCH 3398/5403] drm/amdgpu/atom: Work around vbios NULL offset false positive GCC really does not want to consider NULL (or near-NULL) addresses as valid, so calculations based off of NULL end up getting range-tracked into being an offset wthin a 0 byte array. It gets especially mad about this: if (vbios_str == NULL) vbios_str += sizeof(BIOS_ATOM_PREFIX) - 1; ... if (vbios_str != NULL && *vbios_str == 0) vbios_str++; It sees this as being "sizeof(BIOS_ATOM_PREFIX) - 1" byte offset from NULL, when building with -Warray-bounds (and the coming -fdiagnostic-details flag): In function 'atom_get_vbios_pn', inlined from 'amdgpu_atom_parse' at drivers/gpu/drm/amd/amdgpu/atom.c:1553:2: drivers/gpu/drm/amd/amdgpu/atom.c:1447:34: error: array subscript 0 is outside array bounds of 'unsigned char[0]' [-Werror=array-bounds=] 1447 | if (vbios_str != NULL && *vbios_str == 0) | ^~~~~~~~~~ 'amdgpu_atom_parse': events 1-2 1444 | if (vbios_str == NULL) | ^ | | | (1) when the condition is evaluated to true ...... 1447 | if (vbios_str != NULL && *vbios_str == 0) | ~~~~~~~~~~ | | | (2) out of array bounds here In function 'amdgpu_atom_parse': cc1: note: source object is likely at address zero As there isn't a sane way to convince it otherwise, hide vbios_str from GCC's optimizer to avoid the warning so we can get closer to enabling -Warray-bounds globally. Acked-by: Alex Deucher Signed-off-by: Kees Cook Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/amdgpu/atom.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c index 81d195d366ce..427b073de2fc 100644 --- a/drivers/gpu/drm/amd/amdgpu/atom.c +++ b/drivers/gpu/drm/amd/amdgpu/atom.c @@ -1444,6 +1444,7 @@ static void atom_get_vbios_pn(struct atom_context *ctx) if (vbios_str == NULL) vbios_str += sizeof(BIOS_ATOM_PREFIX) - 1; } + OPTIMIZER_HIDE_VAR(vbios_str); if (vbios_str != NULL && *vbios_str == 0) vbios_str++; -- 2.54.0