linux-kernel - Re: [RFC 6/8] x86_64/bug: Implement __WARN

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Message-ID: <20250602220159.GB39782@noisy.programming.kicks-ass.net>
Date: Tue, 3 Jun 2025 00:01:59 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Linus Torvalds <torvalds@...uxfoundation.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kees@...nel.org,
	acarmina@...hat.com, jpoimboe@...nel.org, mark.rutland@....com
Subject: Re: [RFC 6/8] x86_64/bug: Implement __WARN_printf()

On Mon, Jun 02, 2025 at 11:57:25PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 02, 2025 at 09:38:09AM -0700, Linus Torvalds wrote:
> 
> > And no, I'm not ok with only using 'objdump' and friends to look at
> > assembly generation. I want to be able to do
> > 
> >    make xyz.s
> > 
> > and look at code generation without throwing up.
> 
> So if I stuff the asm macro in a global asm() block then GCC ends up
> looking like so:
> 
>         .set warn_imm, 0
>         warn_add_reg var=warn_imm reg=%rcx      # tmp215
>         .set warn_imm, (warn_imm << 4)
>         warn_add_reg var=warn_imm reg=%rdx      # tmp212
>         1: ud1 warn_imm(%ecx),%rax      # tmp210
>         .pushsection .discard.annotate_insn,"M",@progbits,8
>         .long 1b - .
>         .long 8
>         .popsection
>         .pushsection __bug_table, "aw" ; 123: .long 1b - . ; .long .LC76 - . ; .long .LC0 - . ; .word 8710 ; .word 2321 ; .org 123b + 6 + 4 + 6 ; .popsection   #,,,
> 
> However, clangd is 'helpful' and fully expands the asm macro for the .s
> file :-(

It generates his horror show:

	#APP
.set warn_imm, 0
.set .Lregnr, 0
.set .Lregnr, 1
.set .Lregnr, 2
.set warn_imm, 2
.set .Lregnr, 3
.set .Lregnr, 4
.set .Lregnr, 5
.set .Lregnr, 6
.set .Lregnr, 7
.set .Lregnr, 8
.set .Lregnr, 9
.set .Lregnr, 10
.set .Lregnr, 11
.set .Lregnr, 12
.set .Lregnr, 13
.set .Lregnr, 14
.set .Lregnr, 15
.set .Lregnr, 16
.set .Lregnr, 0
.set .Lregnr, 1
.set .Lregnr, 2
.set .Lregnr, 3
.set .Lregnr, 4
.set .Lregnr, 5
.set .Lregnr, 6
.set .Lregnr, 7
.set .Lregnr, 8
.set .Lregnr, 9
.set .Lregnr, 10
.set .Lregnr, 11
.set .Lregnr, 12
.set .Lregnr, 13
.set .Lregnr, 14
.set .Lregnr, 15
.set .Lregnr, 16
.set warn_imm, 32
.set .Lregnr, 0
.set .Lregnr, 1
.set warn_imm, 33
.set .Lregnr, 2
.set .Lregnr, 3
.set .Lregnr, 4
.set .Lregnr, 5
.set .Lregnr, 6
.set .Lregnr, 7
.set .Lregnr, 8
.set .Lregnr, 9
.set .Lregnr, 10
.set .Lregnr, 11
.set .Lregnr, 12
.set .Lregnr, 13
.set .Lregnr, 14
.set .Lregnr, 15
.set .Lregnr, 16
.set .Lregnr, 0
.set .Lregnr, 1
.set .Lregnr, 2
.set .Lregnr, 3
.set .Lregnr, 4
.set .Lregnr, 5
.set .Lregnr, 6
.set .Lregnr, 7
.set .Lregnr, 8
.set .Lregnr, 9
.set .Lregnr, 10
.set .Lregnr, 11
.set .Lregnr, 12
.set .Lregnr, 13
.set .Lregnr, 14
.set .Lregnr, 15
.set .Lregnr, 16
.Ltmp1656:
	ud1q	33(%ecx), %rax
	.section	.discard.annotate_insn,"M",@progbits,8
.Ltmp1657:
	.long	.Ltmp1656-.Ltmp1657
	.long	8
	.section	.init.text,"ax",@progbits

	.section	__bug_table,"aw",@progbits
.Ltmp1658:
.Ltmp1659:
	.long	.Ltmp1656-.Ltmp1659
.Ltmp1660:
	.long	.L.str.29-.Ltmp1660
.Ltmp1661:
	.long	.L.str-.Ltmp1661
	.short	8710
	.short	2321
.org ((.Ltmp1658+6)+4)+6, 0
	.section	.init.text,"ax",@progbits


	#NO_APP