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Re: RFC: A new MIPS64 ABI
On Feb 14, 2011, at 6:50 PM, David Daney wrote:
> On 02/14/2011 06:33 PM, Matt Thomas wrote:
>>
>> On Feb 14, 2011, at 6:22 PM, David Daney wrote:
>>
>>> On 02/14/2011 04:15 PM, Matt Thomas wrote:
>>>>
>>>> I have to wonder if it's worth the effort. The primary problem I see
>>>> is that this new ABI requires a 64bit kernel since faults through the
>>>> upper 2G will go through the XTLB miss exception vector.
>>>>
>>>
>>> Yes, that is correct. It is a 64-bit ABI, and like the existing n32 ABI requires a 64-bit kernel.
>>
>> N32 doesn't require a LP64 kernel, just a 64-bit register aware kernel.
>> Your N32-big does require a LP64 kernel.
>>
>
> But using 'official' kernel sources the only way to get a 64-bit register aware kernel is for it to also be LP64. So effectively, you do in fact need a 64-bit kernel to run n32 userspace code.
Not all the world is Linux. :) NetBSD supports N32 kernels.
> My proposed ABI would need trivial kernel changes:
>
> o Fix a couple of places where pointers are sign extended instead of zero extended.
I think you'll find there are more of these than you'd expect.
> o Change the stack address and address ranges returned by mmap().
My biggest concern is that many many mips opcodes expect properly
sign-extended value for registers. Thusly N32-big will require
using daddu/dadd/dsub/dsubu for addresses. So that's yet another
departure from N32 which can use addu/add/sub/subu.
> The main work would be in the compiler toolchain and runtime libraries.
You'd also need to update gas for la and dla expansion.