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Date: Sat, 17 Sep 2016 13:54:13 -0500
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
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        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Ingo Molnar <mingo@kernel.org>, Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH] scripts: add script for translating stack dump function
 offsets
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On Sat, Sep 17, 2016 at 11:11:44AM +0200, Vegard Nossum wrote:
> On 16 September 2016 at 21:17, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > On Fri, Sep 16, 2016 at 11:12:10AM -0700, Linus Torvalds wrote:
> >> Side note: I find addr2line almost completely useless in many cases
> >> not because of address space randomization, but because of how complex
> >> the inlining often is. I just had something where I decided to use
> >> addr2line and it just pointed me to the __read_once_size_nocheck()
> >> line in <linux/compiler.h>. That was not very useful.
> >>
> >> I ended up actually looking at the instructions *around* it, to find
> >> where that one instruction had been inlined from.
> >>
> >> So I'm wondering if this kind of helper script could be extended to
> >> have that "look around it" thing to help.
> >
> > I think that issue is solved by addr2line's '--inline' option, which the
> > script uses:
> 
> Another small gotcha is that stack trace addresses are _return
> addresses_, not callsites. So you'll sometimes want to pass 'addr - 1'
> instead of just addr, as the next address (the return address) may
> belong to a completely unrelated deeply inlined function.

Hm, good point.  In that case, should it *always* subtract 1?  (Except
when the offset is already 0, of course.)

-- 
Josh