Re: [PATCH v2] perf tools: Fix arm64 build error with gcc-11

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

On 10/02/2021 03:24, 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. Add ternary operator,
> The statement evaluates to "Unknown" if reg_name==NULL is met.
> 
> Signed-off-by: Jianlin Lv <Jianlin.Lv@arm.com>
> ---
> v2: Add ternary operator to avoid similar errors in other arch.
> ---
>   tools/perf/builtin-script.c                            | 4 +++-
>   tools/perf/util/scripting-engines/trace-event-python.c | 4 +++-
>   tools/perf/util/session.c                              | 5 +++--
>   3 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index 42dad4a0f8cf..d59da3a063d0 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -635,6 +635,7 @@ static int perf_sample__fprintf_regs(struct regs_dump *regs, uint64_t mask,
>   {
>   	unsigned i = 0, r;
>   	int printed = 0;
> +	const char *reg_name;
>   
>   	if (!regs || !regs->regs)
>   		return 0;
> @@ -643,7 +644,8 @@ static int perf_sample__fprintf_regs(struct regs_dump *regs, uint64_t mask,
>   
>   	for_each_set_bit(r, (unsigned long *) &mask, sizeof(mask) * 8) {
>   		u64 val = regs->regs[i++];
> -		printed += fprintf(fp, "%5s:0x%"PRIx64" ", perf_reg_name(r), val);
> +		reg_name = perf_reg_name(r);
> +		printed += fprintf(fp, "%5s:0x%"PRIx64" ", reg_name ?: "Unknown", val);

is it possible not have to do this check for NULL and reassignment 
everywhere?

>   	}
>   
>   	return printed;
> diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
> index c83c2c6564e0..e1222cc6a699 100644
> --- a/tools/perf/util/scripting-engines/trace-event-python.c
> +++ b/tools/perf/util/scripting-engines/trace-event-python.c
> @@ -691,6 +691,7 @@ static int regs_map(struct regs_dump *regs, uint64_t mask, char *bf, int size)
>   {
>   	unsigned int i = 0, r;
>   	int printed = 0;
> +	const char *reg_name;
>   
>   	bf[0] = 0;
>   
> @@ -700,9 +701,10 @@ static int regs_map(struct regs_dump *regs, uint64_t mask, char *bf, int size)
>   	for_each_set_bit(r, (unsigned long *) &mask, sizeof(mask) * 8) {

a good practice is to limit scope of variables as much as possible, so 
reg_name could be declared here
	
>   		u64 val = regs->regs[i++];
>   
> +		reg_name = perf_reg_name(r);
>   		printed += scnprintf(bf + printed, size - printed,
>   				     "%5s:0x%" PRIx64 " ",
> -				     perf_reg_name(r), val);
> +				     reg_name ?: "Unknown", val);
>   	}
>   
>   	return printed;
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index 25adbcce0281..1058d8487e98 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1135,12 +1135,13 @@ static void branch_stack__printf(struct perf_sample *sample, bool callstack)
>   static void regs_dump__printf(u64 mask, u64 *regs)
>   {
>   	unsigned rid, i = 0;
> +	const 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);

super nit: it's "unknown" in util/perf_regs.h::perf_reg_name(), so nice 
to be consistent


>   	}
>   }
>   
> 

thanks,
John