Re: Re: mips n64 porting review

[Rich Felker <dalias@libc.org>]

On Thu, Feb 04, 2016 at 11:27:34PM -0500, Rich Felker wrote:
> On Thu, Feb 04, 2016 at 06:52:47PM -0500, Rich Felker wrote:
> > On Wed, Feb 03, 2016 at 06:36:57PM -0500, Rich Felker wrote:
> > > On Wed, Feb 03, 2016 at 03:41:13PM +0000, Mahesh Bodapati wrote:
> > > > Hi Rich,
> > > > I have attached the patch which has all the MIPS n64 porting work. I
> > > > have created mips64port remote branch on GitHub and the repository
> > > > is https://github.com/MaheshBodapati/musl/tree/mips64port which has
> > > > the broken down patches and the base revision on which I have
> > > > prepared patch is v1.1.12-41-g3abb094.
> > > 
> > > Some preliminary review:
> > 
> > One more thing that came up in reviewing syscall_cp.s was actually a
> > bug copied from existing code in musl, which is fixed by this commit:
> > 
> > http://git.musl-libc.org/cgit/musl/commit/?id=756c8af8589265e99e454fe3adcda1d0bc5e1963
> > 
> > In practice the code seemed to work but it was wrong with respect to
> > ABI requirements.
> > 
> > I think the way you're saving $gp on the stack in sigsetjmp.s is also
> > invalid since that part of the stack will have been clobbered by the
> > time setjmp returns a second time. You could save it inside an unused
> > part of the jump buffer, but it might be better to just avoid the $gp
> > register and instead use temp registers and possibly some pc-relative
> > address computations.
> 
> Likewise in pipe.s, it's overly complicated by the fact that it's
> saving $gp on the stack and thereby can't make a tail call to
> __syscall_ret like it's intended to. If you just use a different
> register instead of $gp that's call-clobbered you can tail-call just
> like the 32-bit mips version. Alternatively it's possible now to write
> src/unistd/mips64/pipe.c instead using inline asm and let the compiler
> handle the nastiness of the calling convention. I'd be happy with
> either approach; the C version is probably mildly nicer, especially if
> the compiler still does the tail-call right and doesn't generate come
> bloated monstrosity. (Note that you can't use C for sigsetjmp though
> because it can't use the stack.)
> 
> At this point I think I've looked through all the mips64 files at
> least once and caught all the important issues.

Ping. Any questions or updates on mips64?

Rich