linux-kernel - Re: [PATCH v3 18/39] x86/ibt,ftrace: Make function-graph play nice

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Message-ID: <20220304194853.GN11184@worktop.programming.kicks-ass.net>
Date:   Fri, 4 Mar 2022 20:48:53 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com, mbenes@...e.cz, rostedt@...dmis.org,
        mhiramat@...nel.org, alexei.starovoitov@...il.com
Subject: Re: [PATCH v3 18/39] x86/ibt,ftrace: Make function-graph play nice

On Fri, Mar 04, 2022 at 09:51:54AM -0800, Josh Poimboeuf wrote:
> On Thu, Mar 03, 2022 at 12:23:39PM +0100, Peter Zijlstra wrote:
> > +
> > +	addq $16, %rsp
> > +	ANNOTATE_INTRA_FUNCTION_CALL
> > +	call .Ldo_rop
> > +	int3
> > +.Ldo_rop:
> > +	mov %rdi, (%rsp)
> > +	UNWIND_HINT_FUNC
> > +	RET
> 
> Why the int3?

Speculation trap :-) Either I'm too paranoid or not paranoid enough; but
without it it's just too close to a retpoline and it doesn't feel right.