On Tue, Apr 23, 2019 at 02:16:53PM +0000, Kazlauskas, Nicholas wrote:
> On 4/23/19 10:10 AM, Dan Carpenter wrote:
> > Hello David Francis,
> >
> > This is a semi-automatic email about new static checker warnings.
> >
> > The patch c238bfe0be9e: "drm/amd/display: If one stream full updates,
> > full update all planes" from Mar 29, 2019, leads to the following
> > Smatch complaint:
> >
> > drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc.c:1492 det_surface_update()
> > warn: variable dereferenced before check 'u->surface' (see line 1467)
> >
> > drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc.c
> > 1466
> > 1467 if (u->surface->force_full_update) {
> > ^^^^^^^^^^^^
> > The patch adds a new dereference
> >
> > 1468 update_flags->bits.full_update = 1;
> > 1469 return UPDATE_TYPE_FULL;
> > 1470 }
> > 1471
> > 1472 type = get_plane_info_update_type(u);
> > 1473 elevate_update_type(&overall_type, type);
> > 1474
> > 1475 type = get_scaling_info_update_type(u);
> > 1476 elevate_update_type(&overall_type, type);
> > 1477
> > 1478 if (u->in_transfer_func)
> > 1479 update_flags->bits.in_transfer_func_change = 1;
> > 1480
> > 1481 if (u->input_csc_color_matrix)
> > 1482 update_flags->bits.input_csc_change = 1;
> > 1483
> > 1484 if (u->coeff_reduction_factor)
> > 1485 update_flags->bits.coeff_reduction_change = 1;
> > 1486
> > 1487 if (u->gamma) {
> > 1488 enum surface_pixel_format format = SURFACE_PIXEL_FORMAT_GRPH_BEGIN;
> > 1489
> > 1490 if (u->plane_info)
> > 1491 format = u->plane_info->format;
> > 1492 else if (u->surface)
> > ^^^^^^^^^^
> > But the old code assumed it could be NULL
>
> This looks like a check that could probably be dropped. This function
> shouldn't be called with a u->surface = NULL - there's even that other
> deference at the top of the function with &u->surface->update_flags;
>
Yeah... Techincally, that's not a dereference though so it doesn't
generate a static checker warning. (It's just taking the address).
But then we dereference the address on the next line when we do
"update_flags->raw = 0;". That code is complicated for static analysis.
regards,
dan carpenter
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