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

[Florian Weimer]

* Carlos O'Donell:

> On 6/26/20 5:05 PM, Florian Weimer via Libc-alpha wrote:
>> * 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.
>
> I mention this in my response to the cover letter in this series.

Your explanation there was truncated.

> This patch is probably unacceptable as-is because of application
> expectations.

But perhaps Cisco's experience shows that our worries are unfounded?

Thanks,
Florian