Re: [PATCH v5 1/4] x86/signal/64: Add a comment about sigcontext->fs and gs

[Stas Sergeev]

17.02.2016 10:21, Ingo Molnar ÐÐÑÐÑ:
> 
> * Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> 
>> +	 * If the kernel ever adds explicit fs, gs, fsbase, and gsbase
>> +	 * save/restore, it will most likely need to be opt-in and use
>> +	 * different context slots.
> 
> Btw., that's not necessarily true: it could also be made opt-out, and a 
> modify_ldt() or any other cleanly identifiable legacy usage/signature that is 
> associated with DOSEMU might trigger the opt-out automatically as well.
But there are the new versions of dosemu that still use
"modify_ldt() or any other cleanly identifiable legacy usage/signature"
and yet wants a new functionality.
Please don't go for such an unreliable heuristic.

> I.e. behaviorally it would still keep the ABI and modern default behavior could 
> still be whatever we want to make it.
You can allow glibc to deal with the opt-ins.
It has symbol versioning system AFAIK exactly for that.