linux-kernel - Re: [PATCH 1/2] perf: support specify vdso path in cmdline

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Message-ID: <d5309643a85144b4abbb8705b6e7bd8e@huawei.com>
Date: Fri, 14 Jun 2024 03:55:05 +0000
From: duchangbin <changbin.du@...wei.com>
To: Adrian Hunter <adrian.hunter@...el.com>
CC: duchangbin <changbin.du@...wei.com>, Peter Zijlstra
	<peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, "Arnaldo Carvalho de
 Melo" <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Nathan
 Chancellor <nathan@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa
	<jolsa@...nel.org>, "Ian Rogers" <irogers@...gle.com>, "Liang, Kan"
	<kan.liang@...ux.intel.com>, "Nick Desaulniers" <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
	"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>
Subject: Re: [PATCH 1/2] perf: support specify vdso path in cmdline

On Thu, Jun 13, 2024 at 01:19:20PM +0300, Adrian Hunter wrote:
> On 13/06/24 12:49, duchangbin wrote:
> > On Thu, Jun 13, 2024 at 11:23:26AM +0300, Adrian Hunter wrote:
> >> On 13/06/24 09:35, Changbin Du wrote:
> >>> The vdso dumped from process memory (in buildid-cache) lacks debugging
> >>> info. To annotate vdso symbols with source lines we need specify a
> >>> debugging version.
> >>>
> >>> For x86, we can find them from your local build as
> >>> arch/x86/entry/vdso/vdso{32,64}.so.dbg. Or they may reside in
> >>> /lib/modules/<version>/vdso/vdso{32,64}.so on Ubuntu. But notice that
> >>> the buildid has to match.
> >>>
> >>> $ sudo perf record -a
> >>> $ sudo perf report --objdump=llvm-objdump \
> >>>   --vdso arch/x86/entry/vdso/vdso64.so.dbg,arch/x86/entry/vdso/vdso32.so.dbg
> >>>
> >>> When doing cross platform analysis, we also need specify the vdso path if
> >>> we are interested in its symbols.
> >>
> >> We already have logic to find debug files, and to deal with a symbol source
> >> (syms_ss) and runtime symbol source (runtime_ss).
> >>
> >> Can't we make that work transparently for vdso so that the user does
> >> not have to.
> >>
> > For Ubuntu, we can find the debug files of vdso in
> > /lib/modules/<version>/vdso/vdso{32,64}.so. These two are debug version.
> > 
> > For local build, seems vdso{32,64}.so.dbg are not installed in /lib/modules/ nor
> > other locations.
> 
> Isn't there /lib/modules/<version>/build symbolic link to follow?
> 
hm, we can try /lib/modules/<version>/build/arch/x86/entry/vdso/vdso*.so.dbg.
Other arches are similar.

So, we will try these pathes internally. And keep '--vdso' if someone really
want a special path. (just like vmlinux)

-- 
Cheers,
Changbin Du