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

From: Adrian Hunter <adrian.hunter@intel.com>
To: Will Deacon <will.deacon@arm.com>
Cc: "acme@redhat.com" <acme@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Kristina Martsenko <Kristina.Martsenko@arm.com>,
	Vladimir Nikulichev <nvs@tbricks.com>,
	Namhyung Kim <namhyung@kernel.org>,
	luto@amacapital.net
Subject: Re: [PATCH] perf tools: don't adjust symbols in vDSO
Date: Fri, 26 Jun 2015 18:35:33 +0300	[thread overview]
Message-ID: <558D7145.3030403@intel.com> (raw)
In-Reply-To: <20150626145835.GD9791@arm.com>

On 26/06/2015 5:58 p.m., Will Deacon wrote:
> (CC'ing Andy, since the removal of VDSO_PRELINK is user-visible here)
> On Fri, Jun 26, 2015 at 02:55:29PM +0100, Adrian Hunter wrote:
>> 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@tbricks.com>
>>>>> Cc: Adrian Hunter <adrian.hunter@intel.com>
>>>>> Cc: Namhyung Kim <namhyung@kernel.org>
>>>>> Reported-by: Kristina Martsenko <kristina.martsenko@arm.com>
>>>>> Signed-off-by: Will Deacon <will.deacon@arm.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
>
> So I just tried that on a core2 box and it's broken even without my patch:
>
> # ./perf record -e cycles:u  ./vdso-test
> [...]
> # ./perf report
> [...]
> # Overhead  Command    Shared Object      Symbol
> # ........  .........  .................  ........................
> #
>      99.70%  vdso-test  [vdso]             [.] __vdso_clock_gettime

Annotation is broken but the symbol gets resolved.