Re: [PATCH] s390/perf: fix 'start' address of module's map

[Songshan Gong]

å 7/27/2016 9:08 PM, Arnaldo Carvalho de Melo åé:
> Em Wed, Jul 27, 2016 at 06:49:48PM +0800, Songshan Gong escreveu:
> > å 7/27/2016 4:29 AM, Arnaldo Carvalho de Melo åé:
> > > Em Tue, Jul 26, 2016 at 10:14:18PM +0200, Christian Borntraeger escreveu:
> > > > On 07/26/2016 09:50 PM, Arnaldo Carvalho de Melo wrote:
> > > > > Em Thu, Jul 21, 2016 at 11:10:51AM +0800, Song Shan Gong escreveu:
> > > > > > At preset, when creating module's map, perf gets 'start' address by parsing
> > > > > > '/proc/modules', but it's module base address, isn't the start address of
> > > > > > '.text' section. In most archs, it's OK. But for s390, it places 'GOT' and
> > > > > > 'PLT' relocations before '.text' section. So there exists an offset between
> > > > > > module base address and '.text' section, which will incur wrong symbol
> > > > > > resolution for modules.
> > > > >
> > > > > I'll apply this as it fixes the problem for you and we need to get fixes
> > > > > in ASAP to get this into 4.8, but why can't we just use your method for
> > > > > all arches and get rid of this arch__ hook? I.e. if I look here in my
> > > > > x86_64 notebook I see:
> > > > >
> > > > > [acme@jouet linux]$ cat /sys/module/tun/sections/.text
> > > > > 0xffffffffc0af2000
> > > > > [acme@jouet linux]$ grep tun /proc/modules
> > > > > tun 28672 4 vhost_net, Live 0xffffffffc0af2000
> > > > > [acme@jouet linux]$
> > > > >
> > > > > So I could as well use what is in /sys/module/tun/sections/.text instead
> > > > > of reading it from /proc/modules and, in s390, reading it from
> > > > > /sys/module/tun/sections/.text.
> > > > >
> > > > > Do you see any problem with using this approach for _all_ arches?
> > > >
> > > > I think it should work well for _all_ arches but it will probably be
> > > > hard to test this without help.
> > >
> > > Well, we could check for the cases we don't know, i.e. read from both
> > > and warn about cases where it is different, except for s390 where we now
> > > which is the right one to pick.
> > One question: how to get arch info except machine->env->arch? It seems that
> > machine->env->arch could be NULL sometimes.
>
> That is not what you want to look at, as it is related to perf.data,
> which may not be related to what you want, which is the running machine.
>
> For that use uname() -> utsname.machine.
>
> But then, why would you need it for reading /sys/module/*/sections/.text?
> The arch name isn't there :-)

Yes, it's no use for this patch. Thanks a lot.
> - Arnaldo

--
SongShan Gong