linux-kernel - Re: [PATCH] x86/hweight: Fix and improve __arch

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Message-ID: <20250310204454.GYZ89PRl3dBR-9oBIY@fat_crate.local>
Date: Mon, 10 Mar 2025 21:44:54 +0100
From: Borislav Petkov <bp@...en8.de>
To: Uros Bizjak <ubizjak@...il.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/hweight: Fix and improve __arch_hweight{32,64}()
 assembly

On Mon, Mar 10, 2025 at 09:35:42PM +0100, Uros Bizjak wrote:
> On Mon, Mar 10, 2025 at 9:12 PM Borislav Petkov <bp@...en8.de> wrote:
> >
> > On Mon, Mar 10, 2025 at 09:08:04PM +0100, Uros Bizjak wrote:
> > > a) Use ASM_CALL_CONSTRAINT to prevent inline asm that includes call
> > > instruction from being scheduled before the frame pointer gets set
> > > up by the containing function, causing objtool to print a "call
> > > without frame pointer save/setup" warning.
> >
> > The other two are ok but this is new. How do you trigger this? I've never seen
> > it in my randconfig builds...
> 
> It is not triggered now, but without this constraint, nothing prevents
> the compiler from scheduling the insn in front of frame creation.

Can you please stop with this silliness?

When we start doing git archeology months, years from now, it should be
perfectly clear why a commit was done. This one is not. So either the compiler
is doing the bad scheduling or it isn't. Things can't just work by chance.

Geez.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette