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Message-ID: <20170801230759.GF1627@brightrain.aerifal.cx>
Date: Tue, 1 Aug 2017 19:07:59 -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 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?
Rich
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