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SubjectRe: [PATCH] perf tools: Fix arm64 build error with gcc-11
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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
> .
>

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