On Mon, Apr 21, 2025 at 5:59 PM Kees Cook <k...@kernel.org> wrote: > > 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. > > Signed-off-by: Kees Cook <k...@kernel.org>
Acked-by: Alex Deucher <alexander.deuc...@amd.com> Do you want me to pick this up, or do you want to take this through some other tree? Thanks, Alex > --- > Cc: Alex Deucher <alexander.deuc...@amd.com> > Cc: "Christian König" <christian.koe...@amd.com> > Cc: Xinhui Pan <xinhui....@amd.com> > Cc: David Airlie <airl...@gmail.com> > Cc: Simona Vetter <sim...@ffwll.ch> > Cc: Jesse Zhang <jesse.zh...@amd.com> > Cc: Tim Huang <tim.hu...@amd.com> > Cc: Srinivasan Shanmugam <srinivasan.shanmu...@amd.com> > Cc: Alexander Richards <electrod...@gmail.com> > Cc: Lijo Lazar <lijo.la...@amd.com> > Cc: Mario Limonciello <mario.limoncie...@amd.com> > Cc: "Gustavo A. R. Silva" <gustavo...@kernel.org> > Cc: amd-gfx@lists.freedesktop.org > Cc: dri-de...@lists.freedesktop.org > --- > 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++; > > -- > 2.34.1 >
