Re: [PATCH] perf tools: Fix arm64 build error with gcc-11

[John Garry <john.garry@huawei.com>]

On 09/02/2021 12:17, Leo Yan wrote:
> Hi Jianlin,
> 
> On Tue, Feb 09, 2021 at 07:33:57PM +0800, Jianlin Lv wrote:
>> gcc version: 11.0.0 20210208 (experimental) (GCC)
>>
>> Following build error on arm64:
>>
>> .......
>> In function ‘printf’,
>>      inlined from ‘regs_dump__printf’ at util/session.c:1141:3,
>>      inlined from ‘regs__printf’ at util/session.c:1169:2:
>> /usr/include/aarch64-linux-gnu/bits/stdio2.h:107:10: \
>>    error: ‘%-5s’ directive argument is null [-Werror=format-overflow=]
>>
>> 107 |   return __printf_chk (__USE_FORTIFY_LEVEL - 1, __fmt, \
>>                  __va_arg_pack ());
>>
>> ......
>> In function ‘fprintf’,
>>    inlined from ‘perf_sample__fprintf_regs.isra’ at \
>>      builtin-script.c:622:14:
>> /usr/include/aarch64-linux-gnu/bits/stdio2.h:100:10: \
>> 	error: ‘%5s’ directive argument is null [-Werror=format-overflow=]
>>    100 |   return __fprintf_chk (__stream, __USE_FORTIFY_LEVEL - 1, __fmt,
>>    101 |                         __va_arg_pack ());
>>
>> cc1: all warnings being treated as errors
>> .......
>>
>> This patch fixes Wformat-overflow warnings by replacing the return
>> value NULL of perf_reg_name with "unknown".
>>
>> Signed-off-by: Jianlin Lv <Jianlin.Lv@arm.com>
>> ---
>>   tools/perf/arch/arm64/include/perf_regs.h | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/arch/arm64/include/perf_regs.h b/tools/perf/arch/arm64/include/perf_regs.h
>> index baaa5e64a3fb..901419f907c0 100644
>> --- a/tools/perf/arch/arm64/include/perf_regs.h
>> +++ b/tools/perf/arch/arm64/include/perf_regs.h
>> @@ -85,10 +85,10 @@ static inline const char *perf_reg_name(int id)
>>   	case PERF_REG_ARM64_PC:
>>   		return "pc";
>>   	default:
>> -		return NULL;
>> +		return "unknown";
>>   	}
>>   
>> -	return NULL;
>> +	return "unknown";
> 
> This issue is a common issue crossing all archs.  So it's better to
> change the code in the places where calls perf_reg_name(), e.g. in
> util/session.c:
> 
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1135,12 +1135,14 @@ static void branch_stack__printf(struct perf_sample *sample, bool callstack)
>   static void regs_dump__printf(u64 mask, u64 *regs)
>   {
>          unsigned rid, i = 0;
> +       char *reg_name;
>   
>          for_each_set_bit(rid, (unsigned long *) &mask, sizeof(mask) * 8) {
>                  u64 val = regs[i++];
>   
> +               reg_name = perf_reg_name(rid);
>                  printf(".... %-5s 0x%016" PRIx64 "\n",
> -                      perf_reg_name(rid), val);
> +                      reg_name ?: "Unknown", val);
>          }
>   }
> 
> And another potential issue is the format specifier "%-5s", it prints
> out maximum to 5 chars, 

Doesn't the width field specify the min, not max, number of characters?

Cheers,
John

> but actually string "Unknown" has 7 chars.
> Actually the format specifier breaks other archs register names, e.g.
> [1][2], seems to me, it's better to change as "%-8s", you might need
> to use a dedicated patch for format specifier changes.
> 
> Thanks,
> Leo
> 
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/powerpc/include/perf_regs.h#n57
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/csky/include/perf_regs.h#n83
> .
>