linux-kernel - Re: [PATCH v2 1/3] kprobes/x86: use instruction_pointer and instruction_pointer

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Date:   Wed, 21 Aug 2019 02:09:10 +0000
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/3] kprobes/x86: use instruction_pointer and
 instruction_pointer_set

Hi,

On Wed, 21 Aug 2019 10:52:47 +0900 Masami Hiramatsu wrote:
> 
> 
> Hi Jisheng,
> 
> On Tue, 20 Aug 2019 09:02:59 +0000
> Jisheng Zhang <Jisheng.Zhang@...aptics.com> wrote:
> 
> > Hi Thomas,
> >
> > On Tue, 20 Aug 2019 10:53:58 +0200 (CEST) Thomas Gleixner wrote:
> >  
> > >
> > >
> > > On Tue, 20 Aug 2019, Jisheng Zhang wrote:
> > >  
> > > > This is to make the x86 kprobe_ftrace_handler() more common so that
> > > > the code could be reused in future.  
> > >
> > > While I agree with the change in general, I can't find anything which
> > > reuses that code. So the change log is pretty useless and I have no idea
> > > how this is related to the rest of the series.  
> >
> > In v1, this code is moved from x86 to common kprobes.c [1]
> > But I agree with Masami, consolidation could be done when arm64 kprobes
> > on ftrace is stable.  
> 
> We'll revisit to consolidate the code after we got 3rd or 4th clones.
> 
> >
> > In v2, actually, the arm64 version's kprobe_ftrace_handler() is the same
> > as x86's, the only difference is comment, e.g
> >
> > /* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */
> >
> > while in arm64
> >
> > /* Kprobe handler expects regs->pc = ip + 1 as breakpoint hit */  
> 
> As Peter pointed, on arm64, is that really 1 or 4 bytes?
> This part is heavily depends on the processor software-breakpoint
> implementation.

Per my understanding, the "+1" here means "+ one kprobe_opcode_t".

> 
> >
> >
> > W/ above, any suggestion about the suitable change log?  
> 
> I think you just need to keep the first half of the description.
> Since this patch itself is not related to the series, could you update
> the description and resend it as a single cleanup patch out of the series?
> 

Got it. Will do today.

Thanks a lot