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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/101544] [OpenMP][AMDGCN][nvptx] C++ offloading:
 unresolved _Znwm = "operator new(unsigned long)"
Date: Wed, 21 Jul 2021 09:33:28 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101544

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Andrew Stubbs from comment #3)
> C++ offloading works fine provided that there are no library calls or
> exceptions.

There's no reason std::pair, std::tuple, std::optional and types like that
shouldn't work.

Just making it possible to compile with -fno-rtti -fno-exceptions would be a
start, and would avoid the need for exception handling. Libstdc++ headers
already work fine with those options, and it should be possible to build the
library itself that way (or it's a bug that can be fixed).

> Ignoring unsupported C++ language features, for now, I don't think there's
> any reason why libstdc++ would need to be cut down. We already build the
> full libgfortran for amdgcn. System calls that make no sense on the GPU w=
ere
> implemented as stubs in Newlib (mostly returning some reasonable errno
> value), and it would be straight-forward to implement more the same way.

But it's a waste of space in the .so to build lots of symbols that use the
stubs.

There are other reasons it might be nice to be able to configure libstdc++ =
for
something in between a full hosted environment and a minimal freestanding o=
ne.

> I believe static constructors work (libgfortran uses some), but exception
> handling does not. I'm not sure what other exotica C++ might need?

Ideally, __cxa_atexit and __cxa_thread_atexit for static and thread-local
destructors, but we can survive without them (and have not-fully-conforming
destruction ordering).=