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

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Message-ID: <20150312202340.GC3550@kernel.org>
Date:	Thu, 12 Mar 2015 17:23:40 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
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

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?

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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