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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 15 Feb 2022, Nathan Chancellor <nathan@kernel.org> wrote:
> 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@gmail.com>
>
> Given this is not enabled for GCC and it is disabled in the main
> Makefile:
>
> Reviewed-by: Nathan Chancellor <nathan@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.

Thanks for the patch and review, pushed to drm-intel-next. I appreciate
the support in maintaining fairly strict warning levels in i915.

BR,
Jani.

>
>> ---
>> 
>> 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
>> 
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center