Date: Wed, 17 Nov 2010 19:31:20 -0600 From: Nathan Whitehorn <nwhitehorn@FreeBSD.org> To: Warner Losh <imp@bsdimp.com> Cc: Tijl Coosemans <tijl@coosemans.org>, Dimitry Andric <dim@FreeBSD.org>, freebsd-arch@FreeBSD.org, John Baldwin <jhb@FreeBSD.org>, Garrett Cooper <gcooper@FreeBSD.org> Subject: Re: Support for cc -m32 Message-ID: <6DDC2926-D359-4269-872A-0A8310AFC1AA@FreeBSD.org> In-Reply-To: <4CE46E94.7040405@bsdimp.com> References: <201007291718.12687.tijl@coosemans.org> <4CE417B3.3030102@bsdimp.com> <201011172058.05683.tijl@coosemans.org> <201011171718.37798.jhb@freebsd.org> <4CE46602.9000303@bsdimp.com> <C96B2549-4BAE-4800-925D-57EA7DFD7733@freebsd.org> <4CE46E94.7040405@bsdimp.com>
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On Nov 17, 2010, at 6:08 PM, Warner Losh wrote:
> On 11/17/2010 16:52, Nathan Whitehorn wrote:
>>
>> On Nov 17, 2010, at 5:32 PM, Warner Losh wrote:
>>
>>> On 11/17/2010 15:18, John Baldwin wrote:
>>>> On Wednesday, November 17, 2010 2:57:51 pm Tijl Coosemans wrote:
>>>>> cc-m32-3.diff:
>>>>> Modify amd64 headers to include i386 headers when compiling
>>>>> 32 bit code.
>>>>>
>>>>> All amd64 headers follow the following format:
>>>>>
>>>>> #ifndef _AMD64_HEADER_H_
>>>>> #define _AMD64_HEADER_H_
>>>>>
>>>>> #ifdef __i386__
>>>>> #include<i386/header.h>
>>>>> #else
>>>>>
>>>>> /* Amd64 declarations go here. */
>>>>>
>>>>> #endif /* __i386__ */
>>>>> #endif /* !_AMD64_HEADER_H_ */
>>>> I find this to be really ugly, and error prone (since it is a
>>>> manual process).
>>>> I'd prefer something that autogenerated headers in /usr/include/
>>>> machine that
>>>> #include the appropriate version similar to what Warner suggested.
>>>>
>>>> However, one issue with that approach (and this one) are headers
>>>> that only
>>>> exist for one platform. The end result would be that that header
>>>> would now
>>>> exist for both platforms (in that if you do 'if [ -r
>>>> /usr/include/machine/foo.h ]' it will be true). We can make it
>>>> #error or
>>>> otherwise fail (by including a non-existing file for example),
>>>> but if there
>>>> was some way to have cc -m32 "magically" substitute "i386/" for
>>>> "machine",
>>>> that is what I would most prefer. (This has problems too in that
>>>> #include
>>>> <machine/foo.h> would work with -m32 even though /usr/include/
>>>> machine/foo.h
>>>> doesn't exist, but /usr/include/i386/foo.h does.
>>> "magically" converting machine -> i386 requires cpp hacking.
>>>
>>> However, the if [] test is beyond the scope of the API that we
>>> support. Scripts that use -m32 will have to cope with other issues.
>>>
>>> We could 'solve' this by having an /usr/include32, but even that
>>> still isn't complete.
>>>
>>> I contend that the least bad solution is to auto generate the
>>> machine directory from the sys/{i386,amd64}/include. If we do
>>> that, we could implement -m64 on i386 too, but that needs a lot
>>> more infrastructure.
>>
>> The other way of solving this, which continues to work very well on
>> powerpc64, is to have the machine/ stuff be identical for the two
>> platforms (which, as far as I can tell, really are the same
>> platform, but with a different ABI) and to use appropriate #ifdefs
>> to select the right things. I would imagine, based on the continued
>> exodus of these headers to x86/ anyway, that the differences are
>> not enormously large. They certainly were not for PPC.
> There's still a number of these that must be in machine :)
Right, I know -- my point was just that clearly amd64/include and i386/
include aren't actually that different, and that maybe they could be
completely merged. MACHINE=x86? :P
>> This could be done either with piece-by-piece modifications of the
>> header files, as was done for PPC, or (perhaps automatically)
>> install some ugly stub headers that look like
>> #ifdef __LP64__
>> #include <amd64/stuff.h>
>> #else
>> #include <i386/stuff.h>
>> #endif
> That's the idea. Automatically generate those and install them
> into /usr/include. I think it is the least bad idea that we have,
> since the more proper way has been rejected.
Ah, OK. I guess my idea wasn't actually original :)
> Actually, I suppose we could add -I/usr/include/32 to the command
> line. David O'Brien said he was going to send me patches to do this,
> but I've not seen them yet. Then we could install i386/include
> into /usr/include/32/machine. This is as close as we can get to
> having it done automatically. The nice part of this is that we can
> make it generic between powerpc, mips and x86 if we wanted.
Are you planning on a /sys/mips64? If not, this is still a special
case just for x86.
-Nathan
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