[PATCH] drm/i915: fix build issue when using clang

[Tong Zhang]

On Sun, Feb 13, 2022 at 10:39 AM Nathan Chancellor <nathan at kernel.org> wrote:
>
> On Sat, Feb 12, 2022 at 10:51:06PM -0800, Tong Zhang wrote:
> > drm/i915 target adds some extra cflags, especially it does re-apply -Wall.
> > In clang this will override -Wno-format-security and cause the build to
> > fail when CONFIG_DRM_I915_WERROR=y. While with GCC this does not happen.
> > We reapply -Wno-format-security here to get around this issue.
>
> For what it's worth, GCC would warn in the exact same way if
> -Wformat-security was included within -Wall like it is for clang:
>
> drivers/gpu/drm/i915/gt/intel_gt.c: In function ‘intel_gt_invalidate_tlbs’:
> drivers/gpu/drm/i915/gt/intel_gt.c:988:9: error: format not a string literal and no format arguments [-Werror=format-security]
>   988 |         GEM_TRACE("\n");
>       |         ^~~~~~~~~
> cc1: all warnings being treated as errors
>
> drivers/gpu/drm/i915/gt/selftest_execlists.c: In function ‘live_sanitycheck’:
> drivers/gpu/drm/i915/gt/selftest_execlists.c:142:25: error: format not a string literal and no format arguments [-Werror=format-security]
>   142 |                         GEM_TRACE("spinner failed to start\n");
>       |                         ^~~~~~~~~
> drivers/gpu/drm/i915/gt/selftest_execlists.c: In function ‘live_preempt’:
> drivers/gpu/drm/i915/gt/selftest_execlists.c:1775:25: error: format not a string literal and no format arguments [-Werror=format-security]
>  1775 |                         GEM_TRACE("lo spinner failed to start\n");
>       |                         ^~~~~~~~~
> drivers/gpu/drm/i915/gt/selftest_execlists.c:1792:25: error: format not a string literal and no format arguments [-Werror=format-security]
>  1792 |                         GEM_TRACE("hi spinner failed to start\n");
>       |                         ^~~~~~~~~
> cc1: all warnings being treated as errors
>
> If fixing these warnings instead of just disabling the warning is
> undesirable (since I feel like the entire point of the i195 cflags
> situation is to enable more warnings than the main Makefile), I think
> the commit message should be rewritten to something along the lines of:
>
> "drm/i915 adds some extra cflags, namely -Wall, which causes
> instances of -Wformat-security to appear when building with clang, even
> though this warning is turned off kernel-wide in the main Makefile:"
>
> > drivers/gpu/drm/i915/gt/intel_gt.c:983:2: error: format string is not a string literal (potentially insecure) [-Werror,-Wformat-security]
> >         GEM_TRACE("ERROR\n");
> >         ^~~~~~~~~~~~~~~~~~~~
> > ./drivers/gpu/drm/i915/i915_gem.h:76:24: note: expanded from macro 'GEM_TRACE'
> >  #define GEM_TRACE(...) trace_printk(__VA_ARGS__)
> >                        ^~~~~~~~~~~~~~~~~~~~~~~~~
> > ./include/linux/kernel.h:369:3: note: expanded from macro 'trace_printk'
> >                 do_trace_printk(fmt, ##__VA_ARGS__);    \
> >                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > ./include/linux/kernel.h:383:30: note: expanded from macro 'do_trace_printk'
> >                 __trace_bprintk(_THIS_IP_, trace_printk_fmt, ##args);   \
> >                                            ^~~~~~~~~~~~~~~~
> > drivers/gpu/drm/i915/gt/intel_gt.c:983:2: note: treat the string as an argument to avoid this
>
> "This does not happen with GCC because it does not enable
> -Wformat-security with -Wall. Disable -Wformat-security within the i915
> Makefile so that these warnings do not show up with clang."
>
> The actual diff itself looks fine to me.
>
> Cheers,
> Nathan
>
> > Signed-off-by: Tong Zhang <ztong0001 at gmail.com>
> > ---
> >  drivers/gpu/drm/i915/Makefile | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> > index 1b62b9f65196..c04e05a3d39f 100644
> > --- a/drivers/gpu/drm/i915/Makefile
> > +++ b/drivers/gpu/drm/i915/Makefile
> > @@ -13,6 +13,7 @@
> >  # will most likely get a sudden build breakage... Hopefully we will fix
> >  # new warnings before CI updates!
> >  subdir-ccflags-y := -Wall -Wextra
> > +subdir-ccflags-y += -Wno-format-security
> >  subdir-ccflags-y += -Wno-unused-parameter
> >  subdir-ccflags-y += -Wno-type-limits
> >  subdir-ccflags-y += -Wno-missing-field-initializers
> > --
> > 2.25.1
> >

Thank you Nathan!
I will send a v2 with a revised commit message.
Thanks,
- Tong