[PATCH v2] drm/i915: fix build issue when using clang

[Nathan Chancellor]

On Mon, Feb 14, 2022 at 11:58:20AM -0800, Tong Zhang wrote:
> 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.
> 
> Signed-off-by: Tong Zhang <ztong0001 at gmail.com>

Given this is not enabled for GCC and it is disabled in the main
Makefile:

Reviewed-by: Nathan Chancellor <nathan at kernel.org>

Additionally, it seems like trace_printk() is designed to be able to
take a string literal without a format argument, so this should be fine.

> ---
> 
> v2: revise commit message
> 
>  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
> 
>