Re: [Libunwind-devel] Fix word size for MIPS architecture

[Faraz Shahbazker]

On 12/05/2014 02:25 AM, Vicente Olivert Riera wrote:
> On 12/02/2014 07:33 PM, Faraz Shahbazker wrote:
> > This should be solved within Xorg build: either by allowing the warning
> > or using --disable-libunwind or an explicit cast to that bit of code.
> By the way, it fails for MIPS32 as well. Of course, if the variable to
> store the words in libunwind is 64bit, and the pointer size of MIPS32 is
> 32bit, when the casting is done, the compilation fails. So, is not only
> MIPS64 n32 but both MIPS32 and MIPS64 n32. The only variant safe is
> MIPS64 n64, which is actually the less common used in the real world.
>
> Build log:
> http://autobuild.buildroot.net/results/87b/87be2c95957f9925c1258812e536df72689fc5da/build-end.log
Yes, that is why I suggested changing the Xorg build above.

I am not sure of the exact reasons for unw_word_t being 64-bit for all 
MIPS. One possibility is support for 64-bit FP registers, which mips32 
(post Revision 2) does allow. FP register support is currently 
broken/unimplemented for MIPS, but that is a different topic. Another is 
the ability to use 32-bit libunwind to unwind a 64-bit process (64-bit 
distributions are often built with a 32-bit userland).

Perhaps, pure MIPS32 can be accommodated by defining unw_word_t to be 
32-bit under #if defined(UNW_LOCAL_ONLY) && (_MIPS_SIM == _ABIO32)? 
You'd still need to change something in your Xorg  build for n32. The 
assumption that size_t/ptrdiff_t match the architecture word size is 
simply not valid for n32.

- Faraz Shahbazker