Re: [PATCH v2] add powerpc64 port

[Bobby Bingham <koorogi@koorogi.info>]

On Thu, Apr 14, 2016 at 03:14:00PM -0400, Rich Felker wrote:
> On Thu, Apr 14, 2016 at 03:01:38AM -0500, Bobby Bingham wrote:
> > On Thu, Apr 14, 2016 at 01:05:07AM +0200, Szabolcs Nagy wrote:
> > > * Bobby Bingham <koorogi@koorogi.info> [2016-04-04 00:26:11 -0500]:
> > > > +++ b/arch/powerpc64/bits/setjmp.h
> > > > @@ -0,0 +1 @@
> > > > +typedef unsigned long long __jmp_buf[66];
> > > 
> > > hm glibc seems to use long[64] with 16byte alignment,
> > > is the size diff because of alignment?
> > 
> > Yes.  Though apparently the glibc setjmp asm has code to detect a
> > misaligned jmp_buf, but its handling of that case ends up overflowing
> > the jmp_buf.
> > 
> > I can make some changes to get our jmp_buf down to 65, but the only ways
> > to get it down to 64 are either with 16 byte alignment, or to have setjmp
> > spill vector registers to the stack first so it can copy them from there
> > to the jmp_buf through a gpr.
> > 
> > How important is it to match glibc here?
> 
> I think you could avoid the need for alignment or increased buffer
> size by positioning the vector registers at
> jmp_buf_end-vector_save_size rounded _down_ to alignment, then
> positioning the grps around them (so, putting the last gpr at the end
> rather than before the vectors if the buffer as a whole is
> misaligned).

Is it valid to do the following?

	jmp_buf a, b;
	if (!setjmp(a)) {
		memcpy(b, a, sizeof a);
		longjmp(b, 1);
	}

If that's valid, and the two jmp_bufs might be aligned differently, then
this wouldn't work.

> 
> But it might be preferable to have the alignment match ABI too. Is
> there any way it can be achieved with just things guaranteed to exist
> by the psABI (is __int128 required by the psABI?) or does it require
> C11 and/or GNUC attributes to get 16-byte alignment?

The ABI does specify __int128.  I can switch jmp_buf to this.

> 
> Rich