MIPS Thread Local Storage Help Request

[Joel Sherrill]

Gedare chatted me and said he didn't see the code in the
linked assembly for rdhwr. It wasn't obvious and I should
have added a bit of commentary.

Look for CPULOCAL. The comments in the CVS log are what
tie it to rdhwr and TLS.

There may be an outer wrapper for this. I don't know.

On 4/28/2014 1:47 PM, Joel Sherrill wrote:
> Hi
>
> This is going to be interesting. MIPS TLS is broken because
> we don't have a trap handler for this. From GCC:
>
> ;; Thread-Local Storage
>
> ;; The TLS base pointer is accessed via "rdhwr $3, $29".  No current
> ;; MIPS architecture defines this register, and no current
> ;; implementation provides it; instead, any OS which supports TLS is
> ;; expected to trap and emulate this instruction.  rdhwr is part of the
> ;; MIPS 32r2 specification, but we use it on any architecture because
> ;; we expect it to be emulated.  Use .set to force the assembler to
> ;; accept it.
> ;;
> ;; We do not use a constraint to force the destination to be $3
> ;; because $3 can appear explicitly as a function return value.
> ;; If we leave the use of $3 implicit in the constraints until
> ;; reload, we may end up making a $3 return value live across
> ;; the instruction, leading to a spill failure when reloading it.
>
> This code from NetBSD appears to be the core part of the
> handler.
>
> http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/mips/mips/locore_mips3.S?only_with_tag=MAIN
>
> If someone can adapt this, then the MIPS will have working
> TLS.
>
> Thanks.
>

-- 
Joel Sherrill, Ph.D.             Director of Research & Development
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