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

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Message-ID: <CAH0uvoiB4EFu4x_87cdoU5DezKcGXyT8OEhrs0qNYW7aDktgnQ@mail.gmail.com>
Date: Wed, 26 Nov 2025 11:01:02 -0800
From: Howard Chu <howardchu95@...il.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, acme@...nel.org, 
	Thomas Richter <tmricht@...ux.ibm.com>, linux-kernel@...r.kernel.org, 
	linux-s390@...r.kernel.org, linux-perf-users@...r.kernel.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

Hi guys,

On Wed, Nov 26, 2025 at 10:57 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Wed, Nov 26, 2025 at 12:12:29PM -0500, Steven Rostedt wrote:
> >
> > Arnaldo,
> >
> > How can I make perf trace not confused by the extra fields in the system
> > call trace events?
> >
> > Ftrace can now show the contents of the system call user space buffers, but
> > it appears that this breaks perf!!!
> >
> > system: syscalls
> > name: sys_enter_write
> > ID: 791
> > format:
> >       field:unsigned short common_type;       offset:0;       size:2; signed:0;
> >       field:unsigned char common_flags;       offset:2;       size:1; signed:0;
> >       field:unsigned char common_preempt_count;       offset:3;       size:1; signed:0;
> >       field:int common_pid;   offset:4;       size:4; signed:1;
> >
> >       field:int __syscall_nr; offset:8;       size:4; signed:1;
> >       field:unsigned int fd;  offset:16;      size:8; signed:0;
> >       field:const char * buf; offset:24;      size:8; signed:0;
> >       field:size_t count;     offset:32;      size:8; signed:0;
> >       field:__data_loc char[] __buf_val;      offset:40;      size:4; signed:0;
> >
> > That new __buf_val appears to confuse perf, but I'm having a hell of a time
> > trying to figure out where it reads it!
>
> I've discussed with Steven and concluded that we should change perf to
> ignore fields with "__data_loc char[]" type in syscalls.  Let me take a
> look.

Thanks, I'll also give it a look.

Thanks,
Howard

>
> Thanks,
> Namhyung
>
>