[PATCH RFC] __builtin_dynamic_object_size with -D_FORTIFY_SOURCE=3

[Florian Weimer]

* Siddhesh Poyarekar:

> Besides the bug, do you think a performance tradeoff should result in
> us having this 2 vs 3 differentiation?  I didn't make the 2 vs 3
> proposal specifically to work around this bug although though it does
> make it easier for us to add support into glibc without blocking on
> llvm fixing it.  In general, dynamic object size checks may end up
> having an additional performance tradeoff (even __bdos without this
> bug will have additional instructions emitted, perhaps even spills,
> making them a wee bit slower) and it may be desirable to have a
> separate fortification level to allow developers to choose.

I really dislike more developer choices.  I think we should experiment
with this with a fixed Clang, and see what the generated code looks like
in practice.

Thanks,
Florian
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