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

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Message-ID: <Z8dRNO1-_1YmIpAv@gmail.com>
Date: Tue, 4 Mar 2025 20:15:00 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Brian Gerst <brgerst@...il.com>, "H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org
Subject: Re: [tip: x86/asm] x86/asm: Make ASM_CALL_CONSTRAINT conditional on
 frame pointers


* Josh Poimboeuf <jpoimboe@...nel.org> wrote:

> On Tue, Mar 04, 2025 at 08:01:58AM -1000, Linus Torvalds wrote:
> > On Tue, 4 Mar 2025 at 07:51, Linus Torvalds
> > <torvalds@...ux-foundation.org> wrote:
> > >
> > > Put another way: the old code has years of testing and is
> > > significantly simpler. The new code is new and untested and more
> > > complicated and has already caused known new problems, never mind any
> > > unknown ones.
> > >
> > > It really doesn't sound like a good trade-off to me.
> 
> I'm utterly confused, what are these new problems you're referring to?
> 
> And how specifically is this more fragile?
> 
> AFAICT, there was one known bug before the patches.  Now there are zero
> known bugs.
> 
> Of course, it's entirely possible the build bots will shake out new
> objtool warnings over the next weeks.  But as of now, I haven't seen
> anything.

In any case I've zapped these two commits from tip:x86/asm for the time 
being:

  x86/asm: Fix ASM_CALL_CONSTRAINT for Clang 19 + KCOV + KMSAN
  x86/asm: Make ASM_CALL_CONSTRAINT conditional on frame pointers

Until there's consensus.

I left the 3 preparatory patches, which make sense as standalone 
cleanups:

  KVM: VMX: Use named operands in inline asm
  x86/hyperv: Use named operands in inline asm
  x86/alternatives: Simplify alternative_call() interface

Thanks,

	Ingo