Re: PATCH: Fix the MIPS ISA ELF setting (Re: RedHat 7.1/mips update)

[Thiemo Seufer <ica2_ts at csv dot ica dot uni-stuttgart dot de>]

H . J . Lu wrote:
[snip]
> I thought 4100 implemented MIPS 3 ISA plus a few and MIPS 3 ISA was a super
> set of MIPS 2 ISA. The main issue is 32bit vs. 64bit. The instructions in
> MIPS 2 ISA are 32bit.

MIPS 3 ISA isn't identical with the assembler's -mips3. -mips3 is an
alias to -march=r4000, which happens to be the first processor
implementing MIPS 3 ISA.

> But MIPS 3 ISA is 64bit.

Not necessarily, MIPS 3 only allows it.

> I guess the real quetion is
> how to generate the 32bit vr4100 binary with the proper setting in the ELF
> header without modifying the source code. I guess "-mgp32 -mfp32" may
> work. But Jim has to try it.

I assume -march=vr4100 -mabi=32 will work for him.

> BTW, I don't quite understand the alias thing for MIPS ISA. I thought
> several MIPS CPUs could implement the same ISA. You can generate binaries
> for that ISA to run on all MIPS CPUs which implement it.

For user space this is mostly true, but the ISA doesn't cover things
like return from exceptions or tlb refills. These are similiar but not
really standardized over the different CPU's.

> Otherwise, we
> may have to have one version of binary for each CPU.

For a kernel this is likely to be necessary.


Thiemo