Re: vdso feature requests from the Go people

[Stijn Volckaert]

Andy Lutomirski schreef op 13/06/2014 17:34:
> On Thu, Jun 12, 2014 at 10:39 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> > On 06/12/2014 09:36 PM, Andy Lutomirski wrote:
> > > 1. Parsing the vDSO is a PITA.  What if we bundled the reference
> > > parser inside the vdso?  Concretely, we could have AT_VDSO_FINDENTRY
> > > point to a function like:
> > >
> > > void *vdso_find_entry(const char *name, const char *version)
> > >
> > > Then things like Go and maybe even musl (and klibc?) could just call
> > > that function.  And we'd never have to worry about maintaining
> > > compatibility with more and more weird vdso parsers.
> > >
> > > Implementing this could be as simple as shoving parse_vdso.c into the
> > > vdso, although vdso2c could help and allow a really simple in-vdso
> > > implementation.
> >
> > I'm not really sure how much of a win that is... you have to parse
> > *something*, and for the vast majority of all implementations there will
> > be a dynamic linker just sitting there, and that is what it *does*.
>
> I'm only aware of two implementations that work like that: glibc and
> musl.  AFAIK neither one even tries to use the vdso when statically
> linked.  IIRC, Bionic doesn't support the vdso at all, and Go has the
> present issue.

Glibc DOES use the VDSO even when it's statically linked. It uses the 
AT_SYSINFO_EHDR it gets from the kernel to find the VDSO and it will 
find any syms it needs dynamically.

--Stijn

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