[Bug libstdc++/64535] Emergency buffer for exception allocation too small

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64535

--- Comment #12 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #11)
> If reading 15.1.4 (Exception Handling / Throwing an exception) correctly
> then allocation happens in an unspecified way but according to 3.7.3.1
> which specifies that if "the allocation function" that fails to allocate
> storage shall throw std::bad_alloc (if not marked with throw ()).  But
> it isn't specified if the "unspecified" EH allocation "function" is
> marked with throw ().

An "allocation function" specifically refers to an overload of operator new.

The reference from 15.1.4 [except.throw] to [basic.stc.dynamic.allocation] is
apparently meant to refer to the final paragraph, which says: "[ Note: In
particular, a global allocation function is not called to allocate storage for
[...] an exception object (15.1). â end note ]" so it's saying that operator
new must not be used to allocate memory for exceptions (but it's OK to use
malloc or a static buffer or both). That means the rules for how operator new
indicates OOM are not relevant for exception handling.

> In particular 15.5.1 (The std::terminate function) doesn't list OOM
> in allocating an exception as cause of abandoning exception handling.
> 
> It would be nice to get clarification from the standards body on what
> shall happen if EH allocation runs into OOM situations.

Undefined behaviour.