linux-kernel - Re: [PATCH v3] tracing/x86: Update syscall trace events to handle new prefixed syscall func names

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Message-ID: <20180418181729.GA4816@light.dominikbrodowski.net>
Date:   Wed, 18 Apr 2018 20:17:29 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>, x86@...nel.org
Subject: Re: [PATCH v3] tracing/x86: Update syscall trace events to handle
 new prefixed syscall func names


On Wed, Apr 18, 2018 at 11:45:09AM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> Arnaldo noticed that the latest kernel is missing the syscall event system
> directory in x86. I bisected it down to d5a00528b58c ("syscalls/core,
> syscalls/x86: Rename struct pt_regs-based sys_*() to __x64_sys_*()").
> 
> The system call trace events are special, as there is only one trace event
> for all system calls (the raw_syscalls). But a macro that wraps the system
> calls creates meta data for them that copies the name to find the system
> call that maps to the system call table (the number). At boot up, it does a
> kallsyms lookup of the system call table to find the function that maps to
> the meta data of the system call. If it does not find a function, then that
> system call is ignored.
> 
> Because the x86 system calls had "__x64_", or "__ia32_" prefixed to the
> "sys" for the names, they do not match the default compare algorithm. As
> this was a problem for power pc, the algorithm can be overwritten by the
> architecture. The solution is to have x86 have its own algorithm to do the
> compare and this brings back the system call trace events.
> 
> Link: http://lkml.kernel.org/r/20180417174128.0f3457f0@gandalf.local.home
> 
> Reported-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> Fixes: d5a00528b58c ("syscalls/core, syscalls/x86: Rename struct pt_regs-based sys_*() to __x64_sys_*()")
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Acked-by: Dominik Brodowski <linux@...inikbrodowski.net>