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

[Vicente Olivert Riera]

On 12/02/2014 07:33 PM, Faraz Shahbazker wrote:
> On 12/02/2014 02:26 AM, Vicente Olivert Riera wrote:
>> On 12/02/2014 02:35 AM, Arun Sharma wrote:
>>> For the specific patch you attached to the bug report, assuming n32
>>> has 64 bit registers: Changing unw_word_t to 32 bit will break
>>> interfaces like:
>>>
>>> unw_get_reg (unw_cursor_t *cursor, int regnum, unw_word_t *valp)
>> Uhm..., I don't think so. Take a look to this:
>>
>> http://www.imgtec.com/mips/architectures/mips64.asp
>>
>> The last part:
>>
>> "[...] the architecture features a 32-bit compatibility mode, in which
>> all registers and addresses are 32-bit wide [...]"
> I think Arun is right. The only ABI for mips32 architecture is o32. All
> others (n64/o64/n32) are for mips64. If a split is made on the basis of
> architecture, n32 would still have to be implemented within the 64-bit
> architecture part and unw_word_t would have to be 64-bit.
> 
> 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

-- 
Vicente Olivert Riera
Graduate Software Engineer, MIPS Platforms
Imagination Technologies Limited
t: +44 (0)113 2429814
www.imgtec.com