linux-kernel - Re: [PATCHv2 3/8] perf probe powerpc: Fix symbol fixup issues due to ELF type

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Message-ID: <20150427050653.GB6113@naverao1-tp.in.ibm.com>
Date:	Mon, 27 Apr 2015 10:36:53 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	mpe@...erman.id.au, ananth@...ibm.com
Subject: Re: [PATCHv2 3/8] perf probe powerpc: Fix symbol fixup issues due to
 ELF type

On 2015/03/12 05:23PM, Arnaldo Carvalho de Melo wrote:
> Em Mon, Dec 15, 2014 at 08:20:33PM +0530, Naveen N. Rao escreveu:
> > If using the symbol table, symbol addresses are not being fixed up
> > properly, resulting in probes being placed at wrong addresses:
> > 
> >   # perf probe do_fork
> >   Added new event:
> >     probe:do_fork        (on do_fork)
> > 
> >   You can now use it in all perf tools, such as:
> > 
> > 	  perf record -e probe:do_fork -aR sleep 1
> > 
> >   # cat /sys/kernel/debug/tracing/kprobe_events
> >   p:probe/do_fork _text+635952
> >   # printf "%x" 635952
> >   9b430
> >   # grep do_fork /boot/System.map
> >   c0000000000ab430 T .do_fork
> > 
> > Fix by checking for ELF type ET_DYN used by ppc64 kernels.
> 
> Sorry if this was answered already, its been a while since this was
> posted/discussed... Are you completely sure this is not a problem on
> !ppc?
> 
> Woudln't it be more conservative to somehow only adjust symbols for this
> ET_DYN type if the arch is ppc? I.e. something like moving that
> adjust_symbols logic to be arch_adjust_symbols(), provide a default and
> then override it for ppc to include also ET_DYN?

I did check and I don't think any other arch kernel uses ET_DYN, but 
yes, being conservative, I could just make this a arch helper. Will do.

- Naveen

> 
> Looking at the other patches...
> 
> - Arnaldo
> 
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> > ---
> >  tools/perf/util/symbol-elf.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> > index 06fcd1b..7ac4e4c 100644
> > --- a/tools/perf/util/symbol-elf.c
> > +++ b/tools/perf/util/symbol-elf.c
> > @@ -683,7 +683,8 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
> >  						     NULL) != NULL);
> >  	} else {
> >  		ss->adjust_symbols = ehdr.e_type == ET_EXEC ||
> > -				     ehdr.e_type == ET_REL;
> > +				     ehdr.e_type == ET_REL ||
> > +				     ehdr.e_type == ET_DYN;
> >  	}
> >  
> >  	ss->name   = strdup(name);
> > -- 
> > 2.1.3
> 

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