Support for cc -m32

Nathan Whitehorn nwhitehorn at freebsd.org
Thu Nov 18 00:52:50 UTC 2010


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.

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
-Nathan


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