linux-kernel - Re: [tip: x86/asm] x86/asm: Make ASM_CALL_CONSTRAINT conditional on frame pointers

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Message-ID: <20250304174556.hva7f2p4uchhh5dd@jpoimboe>
Date: Tue, 4 Mar 2025 09:45:56 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>, brgerst@...il.com,
	linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
	mingo@...nel.org, peterz@...radead.org, tip-bot2@...utronix.de,
	torvalds@...ux-foundation.org, x86@...nel.org
Subject: Re: [tip: x86/asm] x86/asm: Make ASM_CALL_CONSTRAINT conditional on
 frame pointers

On Mon, Mar 03, 2025 at 06:05:07PM -0800, H. Peter Anvin wrote:
> On March 3, 2025 4:57:49 PM PST, Andrew Cooper <andrew.cooper3@...rix.com> wrote:
> >> One more thing: if we remove ASM_CALL_CONSTRAINTS, we will not be able to use the redzone in future FRED only kernel builds.
> >
> >That's easy enough to fix with "|| CONFIG_FRED_EXCLUSIVE" in some
> >theoretical future when it's a feasible config to use.
> >
> >~Andrew
> 
> Assuming it hasn't bitrotted...

If we start using red zone, I'm thinking it should be fairly easy to add
"red zone stack validation" to objtool.  Then the build bots should be
able to shake out pretty quickly where ASM_CALL_CONSTRAINT is needed.

-- 
Josh