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Re: ppc64 vDSO in mainline
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Ulrich Drepper <drepper at redhat dot com>
- Cc: Steve Munroe <sjmunroe at us dot ibm dot com>, Roland McGrath <roland at redhat dot com>, Alan Modra <amodra at bigpond dot net dot au>, Benjamin Herrenschmidt <benh at kernel dot crashing dot org>, libc-alpha at sources dot redhat dot com
- Date: Tue, 29 Mar 2005 07:23:45 +0200
- Subject: Re: ppc64 vDSO in mainline
- References: <OF7669852D.66A49FF8-ON86256FD2.00793F91-86256FD2.007F59B7@us.ibm.com> <42489A68.20806@redhat.com>
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Mon, Mar 28, 2005 at 03:59:36PM -0800, Ulrich Drepper wrote:
> Steve Munroe wrote:
> >3) a function which is currently
> >exported by libc , but a better optimized version (with a different
> >symbol) is also exported by the VDSO.
>
> There is no reason to add any complications or dependency problems for
> this. Just using a pointer in libc itself, a test for NULL and if not,
> jump to the function is enough. The penalty for this extra indication
> if minimal compared to all the other work involved.
Yeah.
Please when thinking about making vDSO symbols directly usable about
prelink as well. What prelink needs is that all libraries stay at the
preferred address (otherwise it falls back to doing normal symbol lookups
on program start up; but as vDSO is mapped by the kernel, kernel will not
know if it should randomize the address or use a fixed one).
If there are any direct symbol lookups into vDSO, prelink would need special
hacks for vDSO and kernel help as it can't rewrite the vDSO even if vDSO
address was always fixed, but if it is randomized (which is desirable),
vDSO just makes prelink unusable on ppc*.
Jakub