On Tuesday, 2 April 2024 09:52:38 CEST Richard W.M. Jones wrote:
> On Tue, Apr 02, 2024 at 07:40:33AM +0200, Andreas Schneider wrote:
> > On Saturday, 30 March 2024 10:37:44 CEST Richard W.M. Jones wrote:
> > > These are just my thoughts on a Saturday morning.  Feedback welcome of
> > > course.
> > 
> > I find the use of the ifunc attribute is really uncommon at this place. I
> > would expect it in ffmpeg or some media codecs. In xz it looks like it is
> > only there to hook in the payload. The software I know normally uses
> > target cloning.
> 
> In hindsight it's suspicious, but it's not generally suspicious for a
> project that needs to generate optimal code for different
> sub-architectures (eg. something that does fast decompression) to use
> the mechanism for that purpose, ifunc.
> 
> That said, ifunc is a very complicated, fragile  but powerful mechanism
> and I'd like to know from the glibc developers what we should
> look out for.  For example:
> 
>  - Is it ever valid for ifunc to take control of functions in another
>    library?  Can this be detected by ld.so?
> 
>  - Can some wrappers be developed to make it both easier and safer?

Well, if it would do that. I took a quick look at xz and didn't see any 
specific code for an architecture flavor like x86_64-v3 or avx related. It 
lacks the implementation for that. All it did was adding the infrastructure 
without using it. I guess that the use of ifunc would is still be very rare.

Target clones is what you normally see.

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