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

[John Baldwin]

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.

-- 
John Baldwin