linux-kernel - Re: [RFC][PATCH 1/2] x86: Provide assembly __bug

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Message-ID: <20241023112217.GJZxjcaV8rBmuPGJnE@fat_crate.local>
Date: Wed, 23 Oct 2024 13:22:17 +0200
From: Borislav Petkov <bp@...en8.de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: david.kaplan@....com, jpoimboe@...hat.com, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [RFC][PATCH 1/2] x86: Provide assembly __bug_table helpers

On Mon, Oct 07, 2024 at 10:32:11AM +0200, Peter Zijlstra wrote:
> +#define ASM_BUGTABLE_FLAGS(at, file, line, flags)			\
> +	.pushsection __bug_table, "aw" ;				\
> +	123:	ASM_BUG_REL(at) ;					\
> +	ASM_BUGTABLE_VERBOSE(file, line) ;				\
> +	.word	flags ;							\
> +	.org 123b + 6 + ASM_BUGTABLE_VERBOSE_SIZE ;			\

I'm guessing this second 6 is the sizeof(long + word) of the second two?

I.e., in here:

asm __inline volatile("1:\t" ".byte 0x0f, 0x0b" "\n"
		      ".pushsection __bug_table, \"aw\" ;
		       123:
		       		.long 1b - . ;
				.long %c0 - . ;
				^^^^^^^^^^^^^
				.word %c1 ;
				.word %c2 ;
				^^^^^^^^^^


				.org 123b + 6 + 6 ;
			.popsection" "\n" ""

Can we add a define for it too instead of a naked 6?

> +	.popsection
>  
>  #define _BUG_FLAGS(ins, flags, extra)					\
>  do {									\
>  	asm_inline volatile("1:\t" ins "\n"				\

s/ins/insn/ while at it.

The usual abbreviation for an "instruction".

> -		     ".pushsection __bug_table,\"aw\"\n"		\
> -		     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"	\
> -		     "\t.word %c0"        "\t# bug_entry::flags\n"	\
> -		     "\t.org 2b+%c1\n"					\
> -		     ".popsection\n"					\
> -		     extra						\
> -		     : : "i" (flags),					\
> -			 "i" (sizeof(struct bug_entry)));		\
> +	    __stringify(ASM_BUGTABLE_FLAGS(1b, %c0, %c1, %c2)) "\n"	\
> +			    extra					\
> +		     : : "i" (__FILE__), "i" (__LINE__),		\
> +			 "i" (flags));					\
>  } while (0)

-- 
Regards/Gruss,
    Boris.

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