Re: [hurd,commited] hurd: Avoid more libc.so local PLTs

[Samuel Thibault <samuel dot thibault at ens-lyon dot org>]

H.J. Lu, on mar. 03 avril 2018 15:14:16 -0700, wrote:
> On Tue, Apr 3, 2018 at 2:55 PM, Samuel Thibault
> <samuel.thibault@ens-lyon.org> wrote:
> > H.J. Lu, on mar. 03 avril 2018 14:41:27 -0700, wrote:
> >> On Tue, Apr 3, 2018 at 2:24 PM, Samuel Thibault
> >> <samuel.thibault@ens-lyon.org> wrote:
> >> > H.J. Lu, on mar. 03 avril 2018 14:16:50 -0700, wrote:
> >> >> On Tue, Apr 3, 2018 at 2:07 PM, Samuel Thibault
> >> >> <samuel.thibault@ens-lyon.org> wrote:
> >> >> > Hello,
> >> >> >
> >> >> > H.J. Lu, on mar. 03 avril 2018 12:26:33 -0700, wrote:
> >> >> >> __libc_longjmp and __libc_siglongjmp are private external functions provided for
> >> >> >> libpthread.  They should never be called inside libc.
> >> >> >
> >> >> > I'm sorry for asking, but are these conventions documented somewhere?
> >> >> > These look like magic to me otherwise:
> >> >>
> >> >> I don't believe they are well documented.
> >> >
> >> > Ok, then I need an answer to my question:
> >> >
> >> >> > why shouldn't they ever be called from libc?
> >> >
> >> > The existing hurd code does use them for catching signals, so I need to
> >> > know how to fix it.
> >>
> >> Use something similar to
> >>
> >> libc_hidden_proto (_setjmp)
> >> libc_hidden_proto (__sigsetjmp)
> >
> > So I'd just add hidden protos & defs to longjmp and siglongjmp?
> >
> 
> setjmp/longjmp.c has
> 
> weak_alias (__libc_siglongjmp, _longjmp)
> weak_alias (__libc_siglongjmp, longjmp)
> 
> Will
> 
> libc_hidden_proto (_longjmp)
> 
> work for you?

Well, _longjmp is the BSD version of longjmp with the semantic of
siglongjmp (actually it's _setjmp which makes the semantic different,
recorded in the jmp_buf). Here we do use longjmp, not _longjmp. Of
course, the end pointer is the same since it's _setjmp which makes
the semantic different, but I'd really rather not make the code more
confusing by using _longjmp while it is actually a longjmp which is
meant.

Samuel