[RFC PATCH 3/3] add r_debug multiple namespaces support

[Florian Weimer]

* Daniel Walker via Libc-alpha:

> diff --git a/elf/link.h b/elf/link.h
> index 0048ad5d4d..5a42511636 100644
> --- a/elf/link.h
> +++ b/elf/link.h
> @@ -61,6 +61,10 @@ struct r_debug
>        } r_state;
>  
>      ElfW(Addr) r_ldbase;	/* Base address the linker is loaded at.  */
> +
> +    /* Link to next r_debug struct. Each r_debug struct represents a
> +       different namespace.  The first r_debug struct is the default.  */
> +    struct r_debug *next;
>    };
>  
>  /* This is the instance of that structure used by the dynamic linker.  */

How has this patch been tested?  I expect that it will cause an abilist
mismatch for the _r_debug symbol in the dynamic linker.

If we go this route to add this capability, I think we have to add a new
symbol version for the _r_debug symbol, and keep the old one at the
previous size.

How is your compatibility experience with the size and version change?
How many tools need updating before they work again?

A different approach would add another symbol (parallel to _r_debug) to
store this data.  This would avoid the need for any immediate tool
updates.

Thanks,
Florian