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Date: Tue, 1 Aug 2017 23:55:56 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: possible bug in setjmp implementation for ppc64

On Tue, Aug 01, 2017 at 07:28:45PM -0500, Bobby Bingham wrote:
> On Tue, Aug 01, 2017 at 07:07:59PM -0400, Rich Felker wrote:
> > On Tue, Aug 01, 2017 at 06:45:33PM -0400, Rich Felker wrote:
> > > On Tue, Aug 01, 2017 at 08:28:27AM +0300, Alexander Monakov wrote:
> > > > On Tue, 1 Aug 2017, Bobby Bingham wrote:
> > > > > I think this either requires having different versions of setjmp/longjmp
> > > > > for static and dynamic libc,
> > > >
> > > > Do you mean for non-pic vs pic objects? As I understand, when libc.a is
> > > > built with -fpic (so it's suitable for static-pie), setjmp-longjmp need
> > > > to preserve saved TOC at (r1+24). So presumably source code would need
> > > > to test #ifdef __PIC__?
> > > >
> > > > > or to increase the size of jmpbuf so we can always save/restore both
> > > > > r2 and the value on the stack, but this would be an ABI change.
> > > >
> > > > Would that work for non-pic, i.e. is (r1+24) a reserved location even in
> > > > non-pic mode? If not, you can't overwrite it from longjmp.
> > >
> > > Pretty much certainly so; there is no separate "non-PIC ABI". PIC code
> > > is just code that doesn't happen to do certain things not permissible
> > > in PIC. It doesn't have additional permissions to do things that
> > > otherwise wouldn't be permitted in "non-PIC code".
> > >
> > > In any case just saving and restoring both is not an ABI change, since
> > > there's plenty of free space (896 bits worth of non-existant signals)
> > > in the jmp_buf due to the "Hurd sigset_t" mess.
> >
> > It might also be possible to manually create both the entry points for
> > setjmp, rather than letting the assembler auto-generate them, in which
> > case I think the choice of which value to save just depends on which
> > entry point was used. Thoughts?
> 
> I like this idea.  It's slightly more complicated than that because of
> the call to setjmp from sigsetjmp, but should still be ok.  I'll work on
> a patch.

Hmm, can you elaborate on the situation with sigsetjmp?

Rich

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