linux-kernel - Re: [PATCH Linux-next] perf test: Fix test case perf trace BTF general tests

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Message-ID: <aR5mTLRWA-SLAFUM@google.com>
Date: Wed, 19 Nov 2025 16:52:28 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Richter <tmricht@...ux.ibm.com>, linux-kernel@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-perf-users@...r.kernel.org,
	acme@...nel.org, agordeev@...ux.ibm.com, gor@...ux.ibm.com,
	sumanthk@...ux.ibm.com, hca@...ux.ibm.com, japo@...ux.ibm.com
Subject: Re: [PATCH Linux-next] perf test: Fix test case perf trace BTF
 general tests

On Wed, Nov 19, 2025 at 12:59:03PM -0500, Steven Rostedt wrote:
> On Tue, 18 Nov 2025 20:36:46 -0800
> Namhyung Kim <namhyung@...nel.org> wrote:
> 
> > > Really? It still uses libtraceevent right? I made sure that this didn't
> > > break trace-cmd and thought that perf would work too.  
> > 
> > It doesn't completely break perf trace but added new parameter for the
> > write syscall at the end.  IIUC perf trace iterates the format fields
> > after __syscall_nr and take them all as syscall parameters.
> 
> Is this a regression? Or can perf be fixed?
> 
> I just ran it and I have this:
> 
>    542.337 ( 0.131 ms): sshd-session/1189 write(fd: 7<socket:[9749]>, buf: , count: 268)                        = 268
> 
> I haven't tried it without the patches. Does it usually show what "buf" is?
> Now with the reading of user space, it can show the content too!

Yep, it reads the content using BPF.  This is on my 6.16 kernel.

  $ sudo perf trace -e write -- /bin/echo hello
  hello
       0.000 ( 0.014 ms): echo/61922 write(fd: 1, buf: hello\10, count: 6)                                 = 6

Thanks,
Namhyung