linux-kernel - Re: [PATCH 1/2] kbuild: consolidate redundant sed script ASM offset generation

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Message-ID: <28460.1492509473@warthog.procyon.org.uk>
Date:   Tue, 18 Apr 2017 10:57:53 +0100
From:   David Howells <dhowells@...hat.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     dhowells@...hat.com, linux-kbuild@...r.kernel.org,
        Matthias Kaehlcke <mka@...omium.org>,
        Michael Davidson <md@...gle.com>,
        Michal Marek <mmarek@...e.com>,
        Jan Beulich <JBeulich@...ell.com>,
        Alexander van Heukelum <heukelum@...tmail.fm>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] kbuild: consolidate redundant sed script ASM offset generation

Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:

> This part ended up in redundant code after touched by multiple
> people.
> 
> [1] Commit 3234282f33b2 ("x86, asm: Fix CFI macro invocations to
> deal with shortcomings in gas") added parentheses for defined
> expressions to support old gas for x86.
> 
> [2] Commit a22dcdb0032c ("x86, asm: Fix ancient-GAS workaround")
> split the pattern into two to avoid parentheses for non-numeric
> expressions.
> 
> [3] Commit 95a2f6f72d37 ("Partially revert patch that encloses
> asm-offset.h numbers in brackets") removed parentheses from numeric
> expressions as well because parentheses in MN10300 assembly have a
> special meaning (pointer access).
> 
> Apparently, there is a conflict between [1] and [3].  After all,
> [3] took precedence, and a long time has passed since then.

There's a conflict between [1] and various assembly code formats.  Some
formats define, say,

	mov	4,r1

to move the number 4 into register r1, and:

	mov	(4),r1

to move the contents of the memory at address 4 into r1.  Therefore, you
cannot simply wrap numeric operands in brackets.  What might work is adding a
'+' on the front, e.g.:

	mov	+(4),r1

David