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

[John Baldwin]

On Wednesday 10 March 2010 10:55:40 am Nathan Whitehorn wrote:
> 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.

Looks good to me.

-- 
John Baldwin