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

[Adrian Hunter]

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@xxxxxxxxxxx>
> > > > > Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> > > > > Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> > > > > Reported-by: Kristina Martsenko <kristina.martsenko@xxxxxxx>
> > > > > Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
> > > > > ---
> > > > >
> > > > > 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.

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