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

[John Baldwin]

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;

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.

The rest of the diff looks fine to me.

-- 
John Baldwin