linux-kernel - Re: [PATCH v2 7/7] tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM

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Message-ID: <20230208213343.40ee15a5@gandalf.local.home>
Date:   Wed, 8 Feb 2023 21:33:43 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     John Stultz <jstultz@...gle.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Yafang Shao <laoar.shao@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel test robot <oliver.sang@...el.com>,
        kbuild test robot <lkp@...el.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Michal Miroslaw <mirq-linux@...e.qmqm.pl>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Petr Mladek <pmladek@...e.com>,
        Kajetan Puchalski <kajetan.puchalski@....com>,
        Lukasz Luba <lukasz.luba@....com>,
        Qais Yousef <qyousef@...gle.com>,
        Daniele Di Proietto <ddiproietto@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 7/7] tools/testing/selftests/bpf: replace open-coded
 16 with TASK_COMM_LEN

On Wed, 8 Feb 2023 21:28:58 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> And this breaks much more than android. It will break trace-cmd, rasdaemon
> and perf (if it's not using BTF). This change very much "Breaks userspace!"
> And requires a kernel workaround, not a user space one.

OK, so it doesn't break perf, trace-cmd and rasdaemon, because the enum is
only needed in the print_fmt part. It can handle it in the field portion.

That is:


system: sched
name: sched_switch
ID: 285
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:char prev_comm[TASK_COMM_LEN];	offset:8;	size:16;	signed:0;
                             ^^^^^^^^^^^^^^                          ^^
                            is ignored                             is used


	field:pid_t prev_pid;	offset:24;	size:4;	signed:1;
	field:int prev_prio;	offset:28;	size:4;	signed:1;
	field:long prev_state;	offset:32;	size:8;	signed:1;
	field:char next_comm[TASK_COMM_LEN];	offset:40;	size:16;	signed:0;
	field:pid_t next_pid;	offset:56;	size:4;	signed:1;
	field:int next_prio;	offset:60;	size:4;	signed:1;

print fmt: "prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==> next_comm=%s next_pid=%d next_prio=%d", REC->prev_comm, REC->prev_pid, REC->prev_prio, (REC->prev_state & ((((0x00000000 | 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 | 0x00000010 | 0x00000020 | 0x00000040) + 1) << 1) - 1)) ? __print_flags(REC->prev_state & ((((0x00000000 | 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 | 0x00000010 | 0x00000020 | 0x00000040) + 1) << 1) - 1), "|", { 0x00000001, "S" }, { 0x00000002, "D" }, { 0x00000004, "T" }, { 0x00000008, "t" }, { 0x00000010, "X" }, { 0x00000020, "Z" }, { 0x00000040, "P" }, { 0x00000080, "I" }) : "R", REC->prev_state & (((0x00000000 | 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 | 0x00000010 | 0x00000020 | 0x00000040) + 1) << 1) ? "+" : "", REC->next_comm, REC->next_pid, REC->next_prio

   ^^^^^^^

Is what requires the conversions. So I take that back. It only breaks
perfetto, and that's because it writes its own parser and doesn't use
libtraceevent.

-- Steve