linux-kernel - Re: [PATCH] perf tools: don't adjust symbols in vDSO

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Date:	Thu, 25 Jun 2015 16:32:13 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Will Deacon <will.deacon@....com>, acme@...hat.com
CC:	linux-kernel@...r.kernel.org, kristina.martsenko@....com,
	Vladimir Nikulichev <nvs@...icks.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH] perf tools: don't adjust symbols in vDSO

On 24/06/15 19:17, Will Deacon wrote:
> Commit 922d0e4d9f04 ("perf tools: Adjust symbols in VDSO") changed the
> ELF symbol parsing so that the vDSO is treated the same as ET_EXEC and
> ET_REL binaries despite being an ET_DYN.
> 
> This causes objdump, which expects relative addresses, not to produce
> any output in conjunction with perf annotate, which cheerfully passes
> absolute addresses when trying to disassemble vDSO functions.
> 
> This patch avoids marking the vDSO as requiring adjustment of symbol
> addresses, allowing the relative program counter to be used instead.
> 
> Cc: Vladimir Nikulichev <nvs@...icks.com>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Reported-by: Kristina Martsenko <kristina.martsenko@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
> 
> Not sure why I've just started seeing this, but it appears to affect
> both x86 and arm64. Also, if I revert the patch above then the issue
> it supposedly fixed doesn't resurface. Maybe it was just masking another
> bug that has since been addressed?

No the problem still appears on older kernels.

Probably could look at the vdso section/program headers to decide if it
needs adjustment or not.

> 
>  tools/perf/util/symbol-elf.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index a7ab6063e038..ba4f9bf2765d 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -706,7 +706,6 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
>  		GElf_Shdr shdr;
>  		ss->adjust_symbols = (ehdr.e_type == ET_EXEC ||
>  				ehdr.e_type == ET_REL ||
> -				dso__is_vdso(dso) ||
>  				elf_section_by_name(elf, &ehdr, &shdr,
>  						     ".gnu.prelink_undo",
>  						     NULL) != NULL);
> 

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