linux-kernel - Re: [PATCH 5/8] objtool: Convert annotations to assembler macros

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Message-ID: <20251208093712.GC3707891@noisy.programming.kicks-ass.net>
Date: Mon, 8 Dec 2025 10:37:12 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 5/8] objtool: Convert annotations to assembler macros

On Sat, Dec 06, 2025 at 01:41:12PM -0800, Josh Poimboeuf wrote:
> Improve code generation readability by converting the objtool
> annotations into assembler macros which are created when annotate.h is
> included.
> 
> Before:
> 
>   .pushsection .discard.annotate_insn, "M", @progbits, 8; .long 1b - ., 8; .popsection
> 
> After:
> 
>   ANNOTATE_REACHABLE loc=1b
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>

> diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
> index 0e8c611bc9e2..770321c908e5 100644
> --- a/arch/x86/include/asm/asm.h
> +++ b/arch/x86/include/asm/asm.h
> @@ -2,15 +2,15 @@
>  #ifndef _ASM_X86_ASM_H
>  #define _ASM_X86_ASM_H
>  
> -#include <linux/annotate.h>
> -
>  #ifdef __ASSEMBLER__
> +# define __ASM_C(a,b)			a
>  # define __ASM_FORM(x, ...)		x,## __VA_ARGS__
>  # define __ASM_FORM_RAW(x, ...)		x,## __VA_ARGS__
>  # define __ASM_FORM_COMMA(x, ...)	x,## __VA_ARGS__,
>  # define __ASM_REGPFX			%
>  #else
>  #include <linux/stringify.h>
> +# define __ASM_C(a,b)			b
>  # define __ASM_FORM(x, ...)		" " __stringify(x,##__VA_ARGS__) " "
>  # define __ASM_FORM_RAW(x, ...)		    __stringify(x,##__VA_ARGS__)
>  # define __ASM_FORM_COMMA(x, ...)	" " __stringify(x,##__VA_ARGS__) ","
> @@ -115,6 +115,10 @@
>  
>  #endif
>  
> +#define DEFINE_MACRO(name)						\
> +	__ASM_C(DEFINE_ ## name,					\
> +		asm(__stringify(DEFINE_ ## name)))
> +
>  #ifndef __ASSEMBLER__
>  static __always_inline __pure void *rip_rel_ptr(void *p)
>  {

> diff --git a/include/linux/annotate.h b/include/linux/annotate.h
> index 1678410efa1b..8b28f1a81ec4 100644
> --- a/include/linux/annotate.h
> +++ b/include/linux/annotate.h
> @@ -3,53 +3,43 @@
>  #define _LINUX_ANNOTATE_H
>  
>  #include <linux/objtool_types.h>
> +#include <linux/stringify.h>
> +#include <asm/asm.h>
> +
> +#define DEFINE___ANNOTATE						\
> +	.macro __ANNOTATE sec, type, loc;				\
> +	.pushsection __ASM_C(\sec, \\sec), "M", @progbits, 8;		\
> +		.long __ASM_C(\loc, \\loc) - .;				\
> +		.long __ASM_C(\type, \\type);				\
> +	.popsection;							\
> +	.endm
> +
> +#define __DEFINE_ANNOTATE(sec, name, type)				\
> +	.macro name loc=910b;						\
> +	910: __ANNOTATE sec, type, __ASM_C(\loc, \\loc);		\
> +	.endm
> +
> +#define DEFINE_ANNOTATE(type)						\
> +	__DEFINE_ANNOTATE(.discard.annotate_insn,			\
> +			  ANNOTATE_ ## type, ANNOTYPE_ ## type)
> +
> +#define DEFINE_ANNOTATE_DATA(type)					\
> +	__DEFINE_ANNOTATE(.discard.annotate_data,			\
> +			  ANNOTATE_ ## type, ANNOTYPE_ ## type)
>  
>  #ifdef CONFIG_OBJTOOL
>  
> +DEFINE_MACRO(__ANNOTATE);
> +DEFINE_MACRO(ANNOTATE(NOENDBR));
> +DEFINE_MACRO(ANNOTATE(RETPOLINE_SAFE));
> +DEFINE_MACRO(ANNOTATE(INSTR_BEGIN));
> +DEFINE_MACRO(ANNOTATE(INSTR_END));
> +DEFINE_MACRO(ANNOTATE(IGNORE_ALTERNATIVE));
> +DEFINE_MACRO(ANNOTATE(INTRA_FUNCTION_CALL));
> +DEFINE_MACRO(ANNOTATE(UNRET_BEGIN));
> +DEFINE_MACRO(ANNOTATE(REACHABLE));
> +DEFINE_MACRO(ANNOTATE(NOCFI));
> +DEFINE_MACRO(ANNOTATE_DATA(DATA_SPECIAL));

Well, that took a bit this Monday morning... :-)

Clever.