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

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Message-ID: <20250313233333.bdkv2xmmj5j6uwjt@jpoimboe>
Date: Thu, 13 Mar 2025 16:33:33 -0700
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	tip-bot2 for Josh Poimboeuf <tip-bot2@...utronix.de>,
	linux-tip-commits@...r.kernel.org,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Brian Gerst <brgerst@...il.com>, x86@...nel.org
Subject: Re: [tip: x86/asm] x86/asm: Make ASM_CALL_CONSTRAINT conditional on
 frame pointers

On Mon, Mar 10, 2025 at 07:49:56AM -0700, H. Peter Anvin wrote:
> >> Alternatively, you can co-opt the gcc BR I already filed on this and
> >> argue there that there are new reasons to support the alternate
> >> construct.
> 
> I should probably clarify that this wasn't flippant, but a serious
> request.
> 
> If this works by accident on existing gcc, and works on clang, that is
> a very good reason for making it the supported way of doing this going
> forward for both compilers. Per-compiler hacks are nasty, and although
> we are pretty good about coping with them in the kernel, some user
> space app developer is guaranteed to get it wrong. 
> 
> Frame pointers are actually more relevant in user space because user
> space tends to be compiled with a wider range of debug and
> architecture options, and of course there is simply way more user
> space code out there.

I opened a gcc bug:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119279

-- 
Josh