linux-kernel - Re: [PATCH v2 00/14] perf: Stream comparison

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Date:   Mon, 23 Mar 2020 21:59:13 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v2 00/14] perf: Stream comparison

Hi Jiri,

On 3/23/2020 7:05 PM, Jiri Olsa wrote:
> On Fri, Mar 13, 2020 at 03:11:04PM +0800, Jin Yao wrote:
>> Sometimes, a small change in a hot function reducing the cycles of
>> this function, but the overall workload doesn't get faster. It is
>> interesting where the cycles are moved to.
> 
> I'm getting compilation fail:
> 
> 	  BUILD:   Doing 'make -j1' parallel build
> 	  CC       util/srclist.o
> 	util/srclist.c: In function ‘srclist__node_new’:
> 	util/srclist.c:388:35: error: ‘%s’ directive output may be truncated writing up to 4095 bytes into a region of size 4091 [-Werror=format-truncation=]
> 	  388 |  snprintf(cmd, sizeof(cmd), "diff %s %s",
> 	      |                                   ^~
> 	......
> 	  456 |  ret = init_src_info(b_path, a_path, rel_path, &node->info);
> 	      |                      ~~~~~~
> 	In file included from /usr/include/stdio.h:867,
> 			 from util/srclist.c:8:
> 	/usr/include/bits/stdio2.h:67:10: note: ‘__builtin___snprintf_chk’ output between 7 and 8197 bytes into a destination of size 4096
> 	   67 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
> 	      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 	   68 |        __bos (__s), __fmt, __va_arg_pack ());
> 	      |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 	cc1: all warnings being treated as errors
> 	mv: cannot stat 'util/.srclist.o.tmp': No such file or directory
> 	make[4]: *** [/home/jolsa/kernel/linux-perf/tools/build/Makefile.build:97: util/srclist.o] Error 1
> 	make[3]: *** [/home/jolsa/kernel/linux-perf/tools/build/Makefile.build:139: util] Error 2
> 	make[2]: *** [Makefile.perf:617: perf-in.o] Error 2
> 	make[1]: *** [Makefile.perf:225: sub-make] Error 2
> 	make: *** [Makefile:70: all] Error 2
> 
> 
> [jolsa@...va ~]$ gcc --version
> gcc (GCC) 9.3.1 20200317 (Red Hat 9.3.1-1)
> 
> jirka
> 

Can you help to add following patch on top of the patch-set? Looks we 
need to check the return value of snprintf for truncation checking.

jinyao@kbl:~/kbl-ws/perf-dev/lck-7589/acme/tools/perf$ git diff
diff --git a/tools/perf/util/srclist.c b/tools/perf/util/srclist.c
index 8060e4855d11..51ca69eaa9fd 100644
--- a/tools/perf/util/srclist.c
+++ b/tools/perf/util/srclist.c
@@ -385,8 +385,12 @@ static int src_info__create_line_mapping(struct 
src_info *info, char *b_path,
                 goto out;
         }

-       snprintf(cmd, sizeof(cmd), "diff %s %s",
-                b_path, a_path);
+       ret = snprintf(cmd, PATH_MAX, "diff %s %s",
+                      b_path, a_path);
+       if (ret == PATH_MAX) {
+               ret = -1;
+               goto out;
+       }

         pr_debug("Execute '%s'\n", cmd);

Thanks
Jin Yao