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Date: Thu, 26 Sep 2019 19:23:50 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: mips fp32/fpxx/fp64 issues, r6 sjlj broken

On Thu, Sep 26, 2019 at 06:45:21PM -0400, Rich Felker wrote:
> Also, mipsr6 (the new mips-family ISA that's not compatible with
> previous mips) always uses the 64-bit register mode. We presently do
> not have setjmp/longjmp code that works with this case at all
> (existing code will wrongly save low 32-bits of 2 registers instead of
> single whole double register); somehow nobody has noticed that this is
> broken. Making this conditional on __mips_isa_rev >= 6 should not be
> hard.

Attached patch should work, but maybe isn't the best thing to do. I
think using sdc1/ldc1 and just even indices like on r6 would also be
valid for pre-r6 mips using fp32 or fpxx abi; with FR=0, it would
save/restore the pair of 32-bit registers, and with FR=1, fp32 code
could not be running anyway, and fpxx code should work fine. However,
mips I lacks the ldc1/stc1 instructions, so at the very least we'd
need to leave the old form in place for mips I. Or maybe use the s.d
and l.d mnemonics that automatically assemble to the right choice
based on the isa level...

BTW, the document I linked in the previous email mentions stuff about
setjmp having to align float args section at runtime, but that does
not seem relevant since the jmp_buf has always been 64-bit aligned, so
I didn't do anything like that. glibc doesn't either.

Rich

View attachment "mips-sjlj.diff" of type "text/plain" (1217 bytes)

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