linux-kernel - RE: [PATCH 2/4] arm64: implement support for static call trampolines

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Message-ID: <7d807624275a4938871f8e433e510e3c@AcuMS.aculab.com>
Date:   Tue, 26 Oct 2021 11:06:11 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Mark Rutland' <mark.rutland@....com>,
        Ard Biesheuvel <ardb@...nel.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        James Morse <james.morse@....com>,
        Quentin Perret <qperret@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: RE: [PATCH 2/4] arm64: implement support for static call trampolines

From: Mark Rutland
> Sent: 26 October 2021 11:37
...
> My preference overall is to keep the trampoline self-contained, and I'd
> prefer to keep the RET inline in the trampoline rather than trying to
> factor it out so that all the control-flow is clearly in one place.
> 
> So I'd prefer that we have the sequence as-is:
> 
> | 0:	.quad 0x0
> | 	bti	c
> | 	< insn >
> | 	ldr	x16, 0b
> | 	cbz	x16, 1f
> | 	br	x16
> | 1:	ret

What is wrong with:
0:	.quad 1f
	bti	c
	< insn >
	ldr	x16, 0b
	br	x16
1:	bti	c
	ret

Self-contained and reasonably easy to read.

	David

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