Request for review/comments: 32-bit compat for non-x86 architectures

[Nathan Whitehorn]

John Baldwin wrote:
> On Wednesday 10 March 2010 9:39:15 am Nathan Whitehorn wrote:
>   
>> John Baldwin wrote:
>>     
>>> On Tuesday 09 March 2010 11:14:27 pm Nathan Whitehorn wrote:
>>>   
>>>       
>>>> The patch at http://people.freebsd.org/~nwhitehorn/compat_freebsd32.diff 
>>>> (pre-generated freebsd32 syscalls stuff is included, which will be done 
>>>> in two steps on commit) provides groundwork for supporting 32-bit 
>>>> compatibility for 64-bit MIPS and PowerPC systems. It has been tested on 
>>>> amd64 and powerpc64, and compile-tested on ia64. There are two main 
>>>> parts to the patch:
>>>>
>>>> 1) COMPAT_IA32 is renamed COMPAT_FREEBSD32, in analogy to 
>>>> COMPAT_LINUX32, etc. This requires updating kernel configurations, but 
>>>> is less painful than filling machine-independent bits of the kernel with 
>>>> #if defined(COMPAT_IA32) || defined(COMPAT_PPC32) || 
>>>> defined(COMPAT_MIPS32) || ..., and is no less descriptive than the old name.
>>>>
>>>> 2) Modifications to the freebsd32 compat layer to support big-endian 
>>>> architectures.
>>>>
>>>> I would appreciate any comments, bugs, or test results on ia64.
>>>>     
>>>>         
>>> This doesn't look right for non-x86 32-bit ABIs:
>>>
>>> Index: sys/kern/imgact_elf.c
>>> ===================================================================
>>> --- sys/kern/imgact_elf.c	(revision 204681)
>>> +++ sys/kern/imgact_elf.c	(working copy)
>>> @@ -1439,7 +1439,7 @@
>>>  		ehdr->e_ident[EI_ABIVERSION] = 0;
>>>  		ehdr->e_ident[EI_PAD] = 0;
>>>  		ehdr->e_type = ET_CORE;
>>> -#if defined(COMPAT_IA32) && __ELF_WORD_SIZE == 32
>>> +#if defined(COMPAT_FREEBSD32) && __ELF_WORD_SIZE == 32
>>>  		ehdr->e_machine = EM_386;
>>>  #else
>>>  		ehdr->e_machine = ELF_ARCH;
>>>   
>>>       
>> Good catch! Such are the dangers of sed. How about defining an 
>> ELF_ARCH32 in machine/elf.h for this case?
>>     
>
> Yes, that sounds good.
>
>   
>>> It would be nice to eliminate having <compat/ia32*> includes in MI code by 
>>> instead including those headers in appropriate headers in <machine/*>.  For 
>>> example, we could change <machine/reg.h> on amd64 and ia64 to include these 
>>> headers, perhaps under an #ifdef COMPAT_FREEBSD32.
>>>
>>> Hmm, actually, I'm quite convinced now that <machine/reg.h> for ia64 and amd64 
>>> should include <compat/ia32/ia32_reg.h> in the #ifdef _KERNEL section to avoid 
>>> polluting those includes in MI code.  I'm not sure what the various 
>>> <machine/fpu.h> includes are for, but fixing ia32_reg.h would be a good first 
>>> step.  It would make your diffs smaller I think.
>>>   
>>>       
>> This is how it works on powerpc64. I didn't modify amd64 and ia64 in 
>> order to avoid making too many changes, but I think you're right that 
>> this is a good idea. I'll add that to the patch when fixing the EM_386 
>> bit you pointed out above.
>>     
>
> Ok, thanks.
>
>   
I've updated the patch to incorporate these two changes, at 
http://people.freebsd.org/~nwhitehorn/compat_freebsd32_2.diff. Due to 
recursive inclusion issues with sys/procfs.h, it also moves prstatus32 
and friends to compat/freebsd32/freebsd32.h from ia32_reg.h. They are 
MI, and seems like a more appropriate place for them anyway.
-Nathan