linux-kernel - Re: [PATCH 2/6] x86: bug: prevent gcc distortions

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Date:   Fri, 18 May 2018 09:58:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <namit@...are.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, nadav.amit@...il.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 2/6] x86: bug: prevent gcc distortions

On Thu, May 17, 2018 at 09:13:58AM -0700, Nadav Amit wrote:
> +asm(".macro __BUG_FLAGS ins:req file:req line:req flags:req size:req\n"
> +    "1:\t \\ins\n\t"
> +    ".pushsection __bug_table,\"aw\"\n"
> +    "2:\t "__BUG_REL(1b)		"\t# bug_entry::bug_addr\n\t"
> +    __BUG_REL(\\file)			"\t# bug_entry::file\n\t"
> +    ".word \\line"			"\t# bug_entry::line\n\t"
> +    ".word \\flags"			"\t# bug_entry::flags\n\t"
> +    ".org 2b+\\size\n\t"
> +    ".popsection\n\t"
> +    ".endm");
> +
> +#define _BUG_FLAGS(ins, flags)                                          \
>  do {									\
> +	asm volatile("__BUG_FLAGS \"" ins "\" %c0 %c1 %c2 %c3"		\
> +		     : : "i" (__FILE__), "i" (__LINE__),                \
> +			 "i" (flags),                                   \
>  			 "i" (sizeof(struct bug_entry)));		\
>  } while (0)

This is an awesome hack, but is there really nothing we can do to make
it more readable? Esp, that global asm doing the macro definition is a
pain to read.

Also, can we pretty please used named operands in 'new' code?