Re: glibc's use of gnu_indirect_function feature - is it backwardscompatible?

[Bryan Ischo <bryan at ischo dot com>]

On 08/15/11 16:25, Carlos O'Donell wrote:
> On Wed, Aug 10, 2011 at 10:33 PM, Bryan Ischo<bryan@ischo.com>  wrote:
> > On 08/10/11 19:20, Carlos O'Donell wrote:
> > > On 8/10/2011 10:12 PM, Bryan Ischo wrote:
> > > > Just looking for confirmation that if I, say, patch my binutils to
> > > > leave the ABI identification alone even if the object "has gnu
> > > > symbols" (in binutils parliance), can I expect things to "just
> > > > work"?
> > > No. It's not "backwards compatibility" it's actually "forwards
> > > compatbility" that you need. You want to run a new binary or
> > > library with an old linker. It isn't going to work.
> > I think of it as glibc having backwards compatibility with older linkers and
> > loaders, but you could look the other way around too.  You say potato, I say
> > potahto :)
> All joking aside, it's not at all like that. You must not use a newer
> glibc with an older dynamic linker, it simply isn't supported.
...
> No, what you really need to do is build glibc and upgrade all the
> pieces it controls e.g. libc, libm, various static pieces used in
> linking both static and shared programs, and ld.so.

Thank you for sticking with this topic and continuing to offer advice.  
You are absolutely right; I learned after thinking that I had succeeded 
that any program that I attempted to run that was linked with/against my 
new gcc/glibc/binutils toolchain required using the dynamic loader built 
as part of that toolchain.

As an alternative to requiring the upgrade of the loader to use the new 
toolchain, I am exploring just statically linking the toolchain so that 
running the toolchain does not require a new loader.  A side benefit is 
that the toochain should be easily relocatable, if my understanding of 
the search paths involved is correct.

Of course anything built using the toolchain will require the new loader 
but since the environment in which the cross-compiled programs will be 
run is easily upgraded to the new loader, this should be easy.

Thanks again for your help,
Bryan