linux-kernel - Re: [PATCH] perf jit: memset variable st using the correct size

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Message-ID: <20160419135221.GF3677@kernel.org>
Date:	Tue, 19 Apr 2016 10:52:21 -0300
From:	rnaldo Carvalho de Melo <acme@...nel.org>
To:	Colin King <colin.king@...onical.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf jit: memset variable st using the correct size

Em Tue, Apr 19, 2016 at 10:47:41AM -0300, rnaldo Carvalho de Melo escreveu:
> Em Tue, Apr 19, 2016 at 12:07:18AM +0100, Colin King escreveu:
> > From: Colin Ian King <colin.king@...onical.com>
> > 
> > The current code is memsetting the struct stat variable st with
> > the size of stat (which turns out to be 1 byte) rather than the
> > size of variable sz.
> 
> Thanks, applied.

BTW, its a obvious bug, but I'll add this to the changeset log to
enlighten others ;-)

  [acme@...et c]$ cc -pedantic sizeof_function.c -o sizeof_function
  sizeof_function.c: In function ‘main’:
  sizeof_function.c:8:46: warning: invalid application of ‘sizeof’ to a function type [-Wpointer-arith]
    printf("sizeof(stat)=%zd, stat=%p\n", sizeof(stat), stat);
                                              ^
  [acme@...et c]$ ./sizeof_function 
  sizeof(stat)=1, stat=0x40063

As my expectation was for this to return sizeof(void *) :-\

- Arnaldo
 
> - Arnaldo
>  
> > Signed-off-by: Colin Ian King <colin.king@...onical.com>
> > ---
> >  tools/perf/util/jitdump.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
> > index 52fcef3..86afe96 100644
> > --- a/tools/perf/util/jitdump.c
> > +++ b/tools/perf/util/jitdump.c
> > @@ -412,7 +412,7 @@ static int jit_repipe_code_load(struct jit_buf_desc *jd, union jr_entry *jr)
> >  		return -1;
> >  	}
> >  	if (stat(filename, &st))
> > -		memset(&st, 0, sizeof(stat));
> > +		memset(&st, 0, sizeof(st));
> >  
> >  	event->mmap2.header.type = PERF_RECORD_MMAP2;
> >  	event->mmap2.header.misc = PERF_RECORD_MISC_USER;
> > @@ -500,7 +500,7 @@ static int jit_repipe_code_move(struct jit_buf_desc *jd, union jr_entry *jr)
> >  	size++; /* for \0 */
> >  
> >  	if (stat(filename, &st))
> > -		memset(&st, 0, sizeof(stat));
> > +		memset(&st, 0, sizeof(st));
> >  
> >  	size = PERF_ALIGN(size, sizeof(u64));
> >  
> > -- 
> > 2.7.4