Re: [PATCH] perf-script: check session->header.env.arch before using it

From: Song Liu <songliubraving@fb.com>
To: LKML <linux-kernel@vger.kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Kernel Team <Kernel-team@fb.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, stable <stable@vger.kernel.org>
Subject: Re: [PATCH] perf-script: check session->header.env.arch before using it
Date: Sat, 16 Oct 2021 00:59:17 +0000	[thread overview]
Message-ID: <18D8F9F1-BF41-4C60-899B-53F6ED76FB2B@fb.com> (raw)
In-Reply-To: <20211004053238.514936-1-songliubraving@fb.com>

Hi Arnaldo, 

Could you please share your comments on this one?

Thanks,
Song

> On Oct 3, 2021, at 10:32 PM, Song Liu <songliubraving@fb.com> wrote:
> 
> When perf.data is not written cleanly, we would like to process existing
> data as much as possible (please see f_header.data.size == 0 condition
> in perf_session__read_header). However, perf.data with partial data may
> crash perf. Specifically, we see crash in perf-script for NULL
> session->header.env.arch.
> 
> Fix this by checking session->header.env.arch before using it to determine
> native_arch. Also split the if condition so it is easier to read.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
> tools/perf/builtin-script.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index 6211d0b84b7a6..7821f6740ac1d 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -4039,12 +4039,17 @@ int cmd_script(int argc, const char **argv)
> 		goto out_delete;
> 
> 	uname(&uts);
> -	if (data.is_pipe ||  /* assume pipe_mode indicates native_arch */
> -	    !strcmp(uts.machine, session->header.env.arch) ||
> -	    (!strcmp(uts.machine, "x86_64") &&
> -	     !strcmp(session->header.env.arch, "i386")))
> +	if (data.is_pipe)  /* assume pipe_mode indicates native_arch */
> 		native_arch = true;
> 
> +	if (session->header.env.arch) {
> +		if (!strcmp(uts.machine, session->header.env.arch))
> +			native_arch = true;
> +		else if (!strcmp(uts.machine, "x86_64") &&
> +			 !strcmp(session->header.env.arch, "i386"))
> +			native_arch = true;
> +	}
> +
> 	script.session = session;
> 	script__setup_sample_type(&script);
> 
> -- 
> 2.30.2
> 