Re: size of exception handling

[Florian Weimer <fweimer@redhat.com>]

* Moritz Strübe:

>> Would you use it if switching from -fno-exceptions to this new
>> approach resulted in an immediate 20% code size increase, without
>> actually using the new error handling feature at all?  What about
>> 10%?
>
> I don't think that it will be that much.

Why?  Have you simulated the code size changes?  I actually ran some
experiments.

> Exceptions are critical errors you need to handle anyway. Thus the
> code size should not increase as the error-handling code should
> already be there.  I can really recommend Herb's talk:
> https://www.youtube.com/watch?v=ARYP83yNAWk , where also talks about
> reducing RTTI overhead and making the C++-lib mostly exception free.

I think the proponents generally underestimate how many functions would
need to change their signature so that they can propagate errors using
the new mechanism.  This leads to very optimistic estimations on size
impact.

> In that talk he mentions that it would be possible using some CPU-Bit
> to return the state.

That's quite hard for us because of the stack protector.  It's unclear
if using the flag is actually beneficial from a code site perspective.
Obviously it depends on the ration between functions and call sites.

Thanks,
Florian