linux-kernel - Re: [PATCH 3/3] perf tools: adjust symbol address

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Message-ID: <20091230131016.GC2956@ghostprotocols.net>
Date:	Wed, 30 Dec 2009 11:10:16 -0200
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] perf tools: adjust symbol address

Em Wed, Dec 30, 2009 at 11:18:55AM +0800, Xiao Guangrong escreveu:
> Using relocation offset adjust symbol address if we get
> kernel symbol name form elf file
> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 79ca6a0..5b58d34 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -19,6 +19,18 @@
>  #define NT_GNU_BUILD_ID 3
>  #endif
>  
> +static s32 relocate_offset;
> +void update_relocate_offset(s32 offset)
> +{
> +	relocate_offset = offset;
> +}
> +
> +static inline void update_kernel_address(GElf_Sym *sym, bool kernel)
> +{
> +	if (kernel)
> +		sym->st_value += relocate_offset;
> +}

This should be done on the dso level, we may process multiple kernels,
some with relocation, some without.

Humm, even at the _map_ level, because then we can just use the normal
map_ip mechanism, this time the not using the identity map stuff, i.e.
we have to get an IP from some event, then subtract the relocate_offset
that will be in map->start.

- Arnaldo
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