linux-kernel - Re: [PATCH 2/6] perf annotate-data: Collect global variables in advance

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Date: Thu, 2 May 2024 16:28:00 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 2/6] perf annotate-data: Collect global variables in advance

On Thu, May 2, 2024 at 11:23 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Thu, May 2, 2024 at 6:50 AM Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> >
> > On Wed, May 01, 2024 at 11:00:07PM -0700, Namhyung Kim wrote:
> > > Currently it looks up global variables from the current CU using address
> > > and name.  But it sometimes fails to find a variable as the variable can
> > > come from a different CU - but it's still strange it failed to find a
> > > declaration for some reason.
> > >
> > > Anyway, it can collect all global variables from all CU once and then
> > > lookup them later on.  This slightly improves the success rate of my
> > > test data set.
> >
> > It would be interesting you could provide examples from your test data
> > set, i.e. after this patch these extra global variables were considered
> > in the test results, with some tool output, etc.

Here's the example:

Before
-----------------------------------------------------------
find data type for 0x6014(PC) at entry_SYSCALL_64+0x7
CU for arch/x86/entry/entry_64.S (die:0x85e1d)
no variable found

After
-----------------------------------------------------------
find data type for 0x6014(PC) at entry_SYSCALL_64+0x7
CU for arch/x86/entry/entry_64.S (die:0x85e1d)
found by addr=0x6014 type_offset=0x14
 type='struct tss_struct' size=0x5000 (die:0x74dbe1)

It was asm code so it doesn't have the type info in the CU.
With this change it can see the type (from a different CU).
It seems we have a per-cpu variable called cpu_tss_rw at
address 0x6000.

  $ nm vmlinux | grep 6000 | grep tss
  0000000000006000 D cpu_tss_rw

Thanks,
Namhyung