-----Original Message-----
From: Leo Yan <redacted>
Sent: Tuesday, July 13, 2021 6:10 PM
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Hunter, Adrian <adrian.hunter@intel.com>; Peter Zijlstra
[off-list ref]; Ingo Molnar [off-list ref]; Mark Rutland
[off-list ref]; Alexander Shishkin
[off-list ref]; Jiri Olsa [off-list ref];
Namhyung Kim [off-list ref]; Thomas Gleixner
[off-list ref]; Borislav Petkov [off-list ref]; x86@kernel.org; H.
Peter Anvin [off-list ref]; Mathieu Poirier
[off-list ref]; Suzuki K Poulose
[off-list ref]; Mike Leach [off-list ref]; linux-
perf-users@vger.kernel.org; linux-kernel@vger.kernel.org;
coresight@lists.linaro.org; linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 10/11] perf env: Set flag for kernel is 64-bit mode

Hi Arnaldo, Adrian,

On Mon, Jul 12, 2021 at 03:14:35PM -0300, Arnaldo Carvalho de Melo wrote:

quoted

Em Sun, Jul 11, 2021 at 06:41:04PM +0800, Leo Yan escreveu:

quoted

It's useful to know that the kernel is running in 32-bit or 64-bit
mode.  E.g. We can decide if perf tool is running in compat mode
from this info.

This patch adds a global variable "kernel_is_64_bit", it's
initialized when a session setups environment, its value is decided
by checking the architecture string.

Signed-off-by: Leo Yan <redacted>
---
 tools/perf/util/env.c | 17 ++++++++++++++++-  tools/perf/util/env.h
|  1 +
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/env.c b/tools/perf/util/env.c index

ebc5e9ad35db..345635a2e842 100644

--- a/tools/perf/util/env.c
+++ b/tools/perf/util/env.c

@@ -11,6 +11,7 @@
 #include <stdlib.h>
 #include <string.h>

+int kernel_is_64_bit;
 struct perf_env perf_env;

Why can't this be in 'struct perf_env'?

Good question.  I considered to add it in struct perf_env but finally I used this
way; the reason is this variable "kernel_is_64_bit" is only used during
recording phase for AUX ring buffer, and don't use it for report.  So seems to
me it's over complexity to add a new field and just wander if it's necessary to
save this field as new feature in the perf header.

I think we store the arch, so if the "kernel_is_64_bit" calculation depends only on arch
then I guess we don't need a new feature at the moment.

Combining the comment from Adrian in another email, I think it's good to add
a new field "compat_mode" in the struct perf_env, and this field will be
initialized in build-record.c.  Currently we don't need to save this value into
the perf file, if later we need to use this value for decoding phase, then we
can add a new feature item to save "compat_mode"
into the perf file's header.

If you have any different idea, please let me know.  Thanks!

Leo

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