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

[Nathan Whitehorn]

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?
> 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.
> The rest of the diff looks fine to me.
>   
Thanks for the comments!
-Nathan