linux-kernel - Re: [PATCH 5/5] x86: ftrace: fix the comments for ftrace_modify_code

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Date:	Sat, 5 Dec 2015 17:52:33 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Li Bin <huawei.libin@...wei.com>, mingo@...hat.com,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org
Subject: Re: [PATCH 5/5] x86: ftrace: fix the comments for
 ftrace_modify_code_direct

On Sat, 5 Dec 2015 18:12:57 +0100 (CET)
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Fri, 4 Dec 2015, Li Bin wrote:
> > --- a/arch/x86/kernel/ftrace.c
> > +++ b/arch/x86/kernel/ftrace.c
> > @@ -106,13 +106,12 @@ ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
> >  	unsigned char replaced[MCOUNT_INSN_SIZE];
> >  
> >  	/*
> > -	 * Note: Due to modules and __init, code can
> > -	 *  disappear and change, we need to protect against faulting
> > -	 *  as well as code changing. We do this by using the
> > -	 *  probe_kernel_* functions.
> > -	 *
> > -	 * No real locking needed, this code is run through
> > -	 * kstop_machine, or before SMP starts.
> > +	 * Note:
> > +	 * We are paranoid about modifying text, as if a bug were to happen, it
> > +	 * could cause us to read or write to someplace that could cause harm.
> > +	 * Carefully read and modify the code with aarch64_insn_*() which uses  
> 
> aarch64_insn_() is related to x86 in which way?
> 
>

The original comment is incorrect and we discussed this with the
arm64 code, and said the other archs need the comment updated as
well. But it seems that Li Bin just cut and pasted the arm64 patch for
the other archs, or at least with x86 (haven't looked at the others
yet). This needs to be fixed.

-- Steve
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