linux-kernel - Re: [RFC] [PATCH] 32-bit pointers in x86-64

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Date:	Wed, 05 Dec 2007 09:31:20 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Luca" <luca.b633@...il.com>, "Andrew Pinski" <pinskia@...il.com>
Cc:	<gcc@....gnu.org>, <binutils@...rceware.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH] 32-bit pointers in x86-64

>>> "Andrew Pinski" <pinskia@...il.com> 25.11.07 19:45 >>>
>On 11/25/07, Luca <luca.b633@...il.com> wrote:
>> 7.1. Add __attribute__((pointer_size(XXX))) and #pragma pointer_size
>> to allow 64-bit pointers in 32-bit mode and viceversa
>
>This is already there, try using __attribute__((mode(DI) )).

Hmm, unless this is a new feature in 4.3, I can't seem to get this to work on
either i386 (using mode DI) or x86-64 (using mode SI). Could you clarify? If
this worked consistently on at least all 64-bit architectures, I would have a
use for it in the kernel (cutting down the kernel size by perhaps several
pages). Btw., I continue to think that the error message 'initializer element
is not computable at load time' on 64-bit code like this

extern char array[];
unsigned int p = (unsigned long)array;

or 32-bit code like this

extern char array[];
unsigned long long p = (unsigned long)array;

is incorrect - the compiler generally has no knowledge what 'array' is (it may
know whether the architecture is generally capable of expressing the
necessary relocation, but if 'array' is really a placeholder for an assembly
level constant, possibly even defined through __asm__() in the same
translation unit, this diagnostic should at best be a warning). I'm pretty
sure I have an open bug for this, but the sad thing is that bugs like this
never appear to really get looked at.

Thanks, Jan

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