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

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Date:   Fri, 10 Sep 2021 11:17:11 -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 11:11:48AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Fri, Sep 10, 2021 at 11:08:02AM -0300, Arnaldo Carvalho de Melo escreveu:
> > 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.
> 
> So below is the minimal fix, the other cases the compiler somehow thinks
> its ok, so I'll keep as is, will just remove the sizeof(string) to
> sizeof(var), as I did below for the offending case.

End result:

diff --git a/tools/perf/util/amd-sample-raw.c b/tools/perf/util/amd-sample-raw.c
index fc1f670e88562b2e..fbb7d61c50489374 100644
--- a/tools/perf/util/amd-sample-raw.c
+++ b/tools/perf/util/amd-sample-raw.c
@@ -106,7 +106,7 @@ static void pr_ibs_op_data2(union ibs_op_data2 reg)
 static void pr_ibs_op_data3(union ibs_op_data3 reg)
 {
 	char l2_miss_str[sizeof(" L2Miss _")] = "";
-	char op_mem_width_str[sizeof(" OpMemWidth __ bytes")] = "";
+	char op_mem_width_str[sizeof(" OpMemWidth _____ bytes")] = "";
 	char op_dc_miss_open_mem_reqs_str[sizeof(" OpDcMissOpenMemReqs __")] = "";
 
 	/*
@@ -114,14 +114,13 @@ static void pr_ibs_op_data3(union ibs_op_data3 reg)
 	 * Ignore L2Miss and OpDcMissOpenMemReqs (and opdata2) if DcMissNoMabAlloc or SwPf set
 	 */
 	if (!(cpu_family == 0x19 && cpu_model < 0x10 && (reg.dc_miss_no_mab_alloc || reg.sw_pf))) {
-		snprintf(l2_miss_str, sizeof(" L2Miss _"),
-			 " L2Miss %d", reg.l2_miss);
-		snprintf(op_dc_miss_open_mem_reqs_str, sizeof(" OpDcMissOpenMemReqs __"),
+		snprintf(l2_miss_str, sizeof(l2_miss_str), " L2Miss %d", reg.l2_miss);
+		snprintf(op_dc_miss_open_mem_reqs_str, sizeof(op_dc_miss_open_mem_reqs_str),
 			 " OpDcMissOpenMemReqs %2d", reg.op_dc_miss_open_mem_reqs);
 	}
 
 	if (reg.op_mem_width)
-		snprintf(op_mem_width_str, sizeof(" OpMemWidth __ bytes"),
+		snprintf(op_mem_width_str, sizeof(op_mem_width_str),
 			 " OpMemWidth %2d bytes", 1 << (reg.op_mem_width - 1));
 
 	printf("ibs_op_data3:\t%016llx LdOp %d StOp %d DcL1TlbMiss %d DcL2TlbMiss %d "