linux-kernel - Re: [PATCH 0/3] perf report: Add support to print a textual representation of IBS raw sample data

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Message-ID: <YTtmwrZ6iy0TzG3l@kernel.org>
Date:   Fri, 10 Sep 2021 11:08:02 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Ian Rogers <irogers@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Michael Petlan <mpetlan@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Robert Richter <robert.richter@....com>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 0/3] perf report: Add support to print a textual
 representation of IBS raw sample data

Em Fri, Sep 10, 2021 at 10:47:16AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Sep 09, 2021 at 04:58:12PM -0500, Kim Phillips escreveu:
> > Hi Arnaldo,
> > 
> > Can you please take a look at applying this series?  Its kernel-side
> > dependent series has already been applied and is in Linus' master.
> 
> Sure, I'm now trying to fix this:
> 
>   CC      /tmp/build/perf/util/amd-sample-raw.o
> util/amd-sample-raw.c: In function ‘evlist__amd_sample_raw’:
> util/amd-sample-raw.c:125:42: error: ‘ bytes’ directive output may be truncated writing 6 bytes into a region of size between 4 and 7 [-Werror=format-truncation=]
>   125 |                          " OpMemWidth %2d bytes", 1 << (reg.op_mem_width - 1));
>       |                                          ^~~~~~
> In file included from /usr/include/stdio.h:866,
>                  from util/amd-sample-raw.c:7:
> /usr/include/bits/stdio2.h:71:10: note: ‘__builtin___snprintf_chk’ output between 21 and 24 bytes into a destination of size 21
>    71 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    72 |                                    __glibc_objsize (__s), __fmt,
>       |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    73 |                                    __va_arg_pack ());
>       |                                    ~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> make[4]: *** [/var/home/acme/git/perf/tools/build/Makefile.build:96: /tmp/build/perf/util/amd-sample-raw.o] Error 1

So, that trick with using sizeof and that string 3 times is cumbersome
and prone to truncation, at least the compiler can't say that the number
you're passing to %2d will have just 2 digits:

[acme@...co c]$ cat printf.c
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
	char bf[64];
	int len = snprintf(bf, sizeof(bf), "%2d", atoi(argv[1]));

	printf("strlen(%s): %u\n", bf, len);

	return 0;
}
[acme@...co c]$ ./printf 1234567
strlen(1234567): 7
[acme@...co c]$

I'm trying to rework this.

- Arnaldo