linux-kernel - Re: [RFC PATCH 1/7] static_call/x86: Add __static_call

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Message-ID: <20201110135315.GO2611@hirez.programming.kicks-ass.net>
Date:   Tue, 10 Nov 2020 14:53:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>,
        Michal Hocko <mhocko@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Michal Hocko <mhocko@...e.com>
Subject: Re: [RFC PATCH 1/7] static_call/x86: Add __static_call_returnl0()

On Tue, Nov 10, 2020 at 02:42:23PM +0100, Frederic Weisbecker wrote:
> On Tue, Nov 10, 2020 at 11:13:07AM +0100, Peter Zijlstra wrote:
> > On Tue, Nov 10, 2020 at 10:55:15AM +0100, Peter Zijlstra wrote:
> > > On Tue, Nov 10, 2020 at 01:56:03AM +0100, Frederic Weisbecker wrote:
> > > 
> > > > [fweisbec: s/disp16/data16, integrate into text_get_insn(), elaborate
> > > >  comment on the resulting insn, emulate on int3 trap, provide validation,
> > > >  uninline __static_call_return0() for HAVE_STATIC_CALL]
> > 
> > > Why did you add full emulation of this? The patch I send to you used the
> > > text_poke_bp(.emulate) argument to have it emulate an actual call to the
> > > out-of-line version of that function.
> > > 
> > > That should work fine and is a lot less code.
> > 
> > For reference; the below is what I send you. Actually doing the
> > __static_call_return0() call while we poke the magic XOR instruction is
> > much simpler.
> 
> Ok I'll get back to that. I'll just tweak a bit static_call_validate()
> so that it is aware of that instruction.

Ah yes indeed!