Messages in this thread | | | Date | Sat, 27 Jun 2015 10:03:54 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] perf tools: don't adjust symbols in vDSO |
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On Fri, Jun 26, 2015 at 04:44:14PM +0100, Andy Lutomirski wrote: > On Fri, Jun 26, 2015 at 8:29 AM, Will Deacon <will.deacon@arm.com> wrote: > > On Fri, Jun 26, 2015 at 04:18:59PM +0100, Andy Lutomirski wrote: > >> On Fri, Jun 26, 2015 at 7:58 AM, Will Deacon <will.deacon@arm.com> wrote: > >> > (CC'ing Andy, since the removal of VDSO_PRELINK is user-visible here) > >> > >> What arch is this? I removed VDSO_PRELINK entirely from x86 a while > >> back, and now x86's vdso has a base address of 0 before relocations, > >> and everything works just fine. > > > > I think this is only x86, since it's the removal of VDSO_PRELINK that > > has changed things. > > > >> (Except one ancient glibc, which fails if the vdso is relocated at > >> all. We no longer support that version of glibc unless you turn off > >> the vdso entirely.) > > > > The problem is that perf expects to objdump portions of the vdso using > > --start-address=foo and --stop-address=bar, but these addresses have changed > > from being offset by VDSO_PRELINK to 0x0. > > > > Thankfully, it looks like perf tool was always broken in this regard, but > > I figured you might like to be aware of the issue. I guess perf just needs > > to add on the load address of the vdso .text section to its relative > > addresses before passing them to objdump. > > > > Given that we've randomized the vdso load address on x86 for years, I > don't see how perf ever worked here. There was a brief period during > which we actually loaded the vdso at the address VDSO_PRELINK, but > that's long gone.
The symbol resolution works by applying the vdso symbol offset to the [vdso] vma base, but perf annotate had indeed been broken the whole time.
> Is there a patch I should be looking at?
I've cooked something, so I'll send it out now.
Will
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