linux-kernel - Re: [GIT PULL 00/13] Annotation improvements (G+ edition)

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Message-ID: <20120425103132.GB17992@infradead.org>
Date:	Wed, 25 Apr 2012 07:31:32 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Hagen Paul Pfeifer <hagen@...u.net>
Subject: Re: [GIT PULL 00/13] Annotation improvements (G+ edition)

CCing Hagen, who also reported this crash on G+.

Em Wed, Apr 25, 2012 at 09:05:38AM +0200, Ingo Molnar escreveu:
> The new output looks very (very!) nice - but it is still a bit 
> fragile:

Glad you liked it :-)
 
> earth5:~/tip/tools/perf> ./perf record -a sleep 1
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.092 MB perf.data (~4008 samples) ]
> 
> earth5:~/tip/tools/perf> ./perf annotate _int_free
> perf: Segmentation fault
> 
> The crash happens here:
> 
> Program received signal SIGSEGV, Segmentation fault.
> 0x0000000000486cda in annotate_browser__mark_jump_targets (size=<optimized out>, 
>     browser=<optimized out>) at ui/browsers/annotate.c:704
> 704			bdlt->jump_target = true;
> 
> But other than that the new assembly output is awesome :-)

Humm...

683 static void annotate_browser__mark_jump_targets(struct annotate_browser *browser,
684							size_t size)
685	{
686		u64 offset;
687	
688		for (offset = 0; offset < size; ++offset) {
689			struct disasm_line *dl = browser->offsets[offset], *dlt;
690			struct browser_disasm_line *bdlt;
691	
692			if (!dl || !dl->ins || !ins__is_jump(dl->ins))
693				continue;
694	
695			if (dl->ops.target >= size) {
696				ui__error("jump to after symbol!\n"
697					  "size: %zx, jump target: %" PRIx64,
698					  size, dl->ops.target);
699				continue;
700			}
701	
702			dlt = browser->offsets[dl->ops.target];
703			bdlt = disasm_line__browser(dlt);
704			bdlt->jump_target = true;
705		}
706			
707	}

(gdb) p size
$5 = 2415
(gdb) p offset
$6 = 140
(gdb) p dl->ops.target
$7 = 143
(gdb) p browser->offsets[143]
$8 = (struct disasm_line *) 0x0
(gdb) p dl->name
$9 = 0x2363bd0 "je"
(gdb)

Really strange, the code assumed that at the jump target we would have an
assembly line, but only in the previous instruction offset we have a 'lock':

(gdb) p browser->offsets[144]
$10 = (struct disasm_line *) 0x0
(gdb) p browser->offsets[142]
$11 = (struct disasm_line *) 0x27bd620
(gdb) p browser->offsets[142]->name
$12 = 0x237a8a0 "lock"
(gdb)

I'll study this more, but for now I'll just check if there is a disasm_line
at dl->ops.target, i.e. a valid jump target.

- Arnaldo
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