linux-kernel - Re: [PATCH] arm64: ftrace: Fix to enable syscall events on arm64

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Date:   Wed, 28 Nov 2018 08:55:55 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Will Deacon <will.deacon@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        AKASHI Takahiro <takahiro.akashi@...aro.org>
Subject: Re: [PATCH] arm64: ftrace: Fix to enable syscall events on arm64

Hi Will,

On Tue, 27 Nov 2018 13:18:59 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Tue, 27 Nov 2018 16:58:49 +0000
> Will Deacon <will.deacon@....com> wrote:
> 
> > This looks fine to me, but I'm curious about whether this is supposed to
> > work with compat syscalls as well, where the prefix is "__arm64_compat_".
> > 
> > If we broadly follow the x86 lead, we'd have:
> > 
> > 	return (!strncmp(sym, "__arm64_", 8) && !strcmp(sym + 8, name)) ||
> > 		(!strncmp(sym, "__arm64_compat_", 15) && !strcmp(sym + 15, name));
> > 
> > Do we need to handle compat (i.e. 32-bit) tasks here?
> 
> Only if you want to trace compat syscalls as well ;-)

Actually I thought about that, but I found below comment in
arch/arm64/include/asm/ftrace.h

 * Because AArch32 mode does not share the same syscall table with AArch64,
 * tracing compat syscalls may result in reporting bogus syscalls or even
 * hang-up, so just do not trace them.

That's why I dropped compat syscall support.

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>