ABI Question

J.F. · Post by **J.F.** » Sun Feb 27, 2005 1:20 pm

I was looking at something and ran into a question - what ABI does the EE gcc use? Be specific as there are a dozen MIPS ABIs floating around. I don't think I've seen this mentioned anywhere in the examples and what-not.

Thanks.

Post by **mrbrown** » Sun Feb 27, 2005 4:04 pm

Cygnus' EABI.

J.F. · Post by **J.F.** » Mon Feb 28, 2005 4:00 am

That was helpful... a little googoling turned up this:
http://sources.redhat.com/ml/binutils/2 ... 00436.html

Could someone please look this over and see if there are any differences to the EE abi the toolchain builds?

Post by **mrbrown** » Mon Feb 28, 2005 6:40 am

The EABI used in GCC for the EE uses 64-bit longs, and 32-bit pointers. Stack alignment is 16 bytes, not 8. IIRC, structs with 8 or fewer bytes are passed as values as opposed to 4 given in the spec. Perhaps pixel knows more about that, 'cause I also seem to remember that value being 16 at some point. It would make sense if it's 16 bytes because that's the most data a EE register can hold.

Everything else looks OK.

J.F. · Post by **J.F.** » Mon Feb 28, 2005 12:00 pm

That's the kind of info some programmers need. We should probably make a doc for PS2Dev that details the EABI the toolchain gcc uses. We could start with something like the message I linked to above, then make the appropriate changes where needed.

Post by **mrbrown** » Mon Feb 28, 2005 2:14 pm

Thanks for volunteering!

Post by **pixel** » Mon Feb 28, 2005 7:35 pm

mrbrown wrote:The EABI used in GCC for the EE uses 64-bit longs, and 32-bit pointers. Stack alignment is 16 bytes, not 8. IIRC, structs with 8 or fewer bytes are passed as values as opposed to 4 given in the spec. Perhaps pixel knows more about that, 'cause I also seem to remember that value being 16 at some point. It would make sense if it's 16 bytes because that's the most data a EE register can hold.

Everything else looks OK.

Never looked at how ee-gcc handles structs-passed-as-arguments. But it would sound strange since even though 16-bytes is the biggest thing EE can handle in its registers, gcc doesn't know about how to do anything with that apart of load and store. Trying...

-----

With a 16-bytes structure passed on first argument of a function, a0 contains a pointer to the structure.
With a 8-bytes structure passed on first argument of a function, the structure is contained straight inside the stack.
With a 4-bytes structure passed on first argument of a function, the structure is inside a0.

Post by **mrbrown** » Mon Feb 28, 2005 10:24 pm

Ah - interesting that it would put it on the stack, but I guess according to the EABI it's a parameter.

It would be cool if 16 bytes were supported, and MMI instructions were used by the compiler to "depack" the register :).

Post by **pixel** » Mon Feb 28, 2005 10:36 pm

mrbrown wrote:It would be cool if 16 bytes were supported, and MMI instructions were used by the compiler to "depack" the register :).

Thanks for volunteering ^_^

J.F. · Post by **J.F.** » Tue Mar 01, 2005 10:55 am

I'd be glad to put together the ABI spec file. Just keep the comments on various things coming and I'll make the changes in the base spec file. I might also post a question or two when I spot something that needs clarification.
:)