linux-kernel - Re: [PATCH] perf tools: don't adjust symbols in vDSO

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Date:	Fri, 26 Jun 2015 16:55:29 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Will Deacon <will.deacon@....com>
CC:	"acme@...hat.com" <acme@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kristina Martsenko <Kristina.Martsenko@....com>,
	Vladimir Nikulichev <nvs@...icks.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH] perf tools: don't adjust symbols in vDSO

On 26/06/15 15:23, Will Deacon wrote:
> On Thu, Jun 25, 2015 at 02:32:13PM +0100, Adrian Hunter wrote:
>> On 24/06/15 19:17, Will Deacon wrote:
>>> Commit 922d0e4d9f04 ("perf tools: Adjust symbols in VDSO") changed the
>>> ELF symbol parsing so that the vDSO is treated the same as ET_EXEC and
>>> ET_REL binaries despite being an ET_DYN.
>>>
>>> This causes objdump, which expects relative addresses, not to produce
>>> any output in conjunction with perf annotate, which cheerfully passes
>>> absolute addresses when trying to disassemble vDSO functions.
>>>
>>> This patch avoids marking the vDSO as requiring adjustment of symbol
>>> addresses, allowing the relative program counter to be used instead.
>>>
>>> Cc: Vladimir Nikulichev <nvs@...icks.com>
>>> Cc: Adrian Hunter <adrian.hunter@...el.com>
>>> Cc: Namhyung Kim <namhyung@...nel.org>
>>> Reported-by: Kristina Martsenko <kristina.martsenko@....com>
>>> Signed-off-by: Will Deacon <will.deacon@....com>
>>> ---
>>>
>>> Not sure why I've just started seeing this, but it appears to affect
>>> both x86 and arm64. Also, if I revert the patch above then the issue
>>> it supposedly fixed doesn't resurface. Maybe it was just masking another
>>> bug that has since been addressed?
>>
>> No the problem still appears on older kernels.
> 
> Can you be more specific, please? I tried with a 3.16 kernel (that I happen

3.13 Ubuntu kernel

> to be running on my box) but perf doesn't even detect the vdso there,
> regardless of this patch.

Don't know what you mean about not detecting vdso

> 
>> Probably could look at the vdso section/program headers to decide if it
>> needs adjustment or not.
> 
> Did the x86 kernel change in this regard? Why isn't the vDSO always ET_DYN?

I guess, but it is ET_DYN


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