Date: Thu, 4 Feb 2016 23:27:34 -0500 From: Rich Felker <dalias@...c.org> To: Mahesh Bodapati <Mahesh.Bodapati@...tec.com> Cc: Szabolcs Nagy <nsz@...t70.net>, Jaydeep Patil <Jaydeep.Patil@...tec.com>, Anand Takale <Anand.Takale@...tec.com>, musl@...ts.openwall.com Subject: Re: Re: mips n64 porting review 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. Rich
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