linux-kernel - Re: [PATCH] x86: fix CFI macro invocations to deal with shortcomings in gas

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Date:	Wed, 20 Oct 2010 07:43:26 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Alexander van Heukelum" <heukelum@...tmail.fm>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: fix CFI macro invocations to deal with
	 shortcomings in gas

>>> On 19.10.10 at 23:03, "Alexander van Heukelum" <heukelum@...tmail.fm> wrote:
>> -       pushl_cfi (TI_sysenter_return-THREAD_SIZE+8+4*4)(%esp)
>> +       pushl_cfi TI_sysenter_return-THREAD_SIZE_asm+8+4*4(%esp)
> 
> This expands to:
>     pushl_cfi (60)-(8192)+8+4*4(%esp)
> 
> I'm sorry to say that Ubuntu 6.06's gas (2.16.91 20060118) still chokes
> with "too many positional arguments" on this line.

It escapes me where it would split the obviously single argument, and
I know I checked all official versions from 2.15 onwards. Could you
try whether that specific gas would be okay with

     pushl_cfi ((60)-(8192)+8+4*4)(%esp)

I had intentionally removed the surrounding parentheses since
those are considered by newer gas when determining arguments,
and thus I could expose eventual problems with older gas even
on newer versions.

Further, could you experiment (or ideally debug) where is splits
the argument. Something like

.macro m arg1 arg2=0
	.long	\arg1, \arg2
.endm

.data
_start:
	m	(60)-(8192)+8+4*4

might be handy - assembling with -alm=<filename> should allow
you to inspect where the argument got split.

Thanks, Jan

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