Date: Tue, 30 Jan 2024 13:30:54 +0000 From: Lexi Winter <lexi@le-fay.org> To: freebsd-arch@freebsd.org Subject: improving C++ libc headers Message-ID: <Zbj6DuTgT7i88Zkd@ilythia.eden.le-fay.org>
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hi list,
i am considering working up a patch to improve C++ libc headers in FreeBSD.
the problem with the current headers (which come from clang/libc++) is
that this code compiles:
------
#include <cstdlib>
auto main() -> int {
exit(0);
}
------
this should be a compile-time error, because <cstdio> does not declare
::exit[0]. however, it works because <cstdlib> is implemented like
this:
------
#include <stdlib.h> // exposes ::exit()
namespace std {
using ::exit;
// ...
}
------
i would like to replace this with an implementation that does this
instead:
------
namespace std {
extern "C" void exit(int);
// ...
}
------
i have done a very quick proof of concept for this and it does work;
there are some more complicated edge cases, but nothing that can't be
dealt with from what i can see.
but before i put any amount of significant effort into this, i'd like to
check if this is something that is likely to be merged.
to address some potential objections:
- i don't believe this can be handled upstream in libc++, because some
of these headers require knowledge of the implementation - <cstdio>
needs to know about 'struct __sFILE', for example.
- "import std" should solve this properly, but there are a lot of
implementation issues with this and it's not clear if/when it will
ever be supported; in the mean time, the existing standard headers
should behave correctly.
[0] https://www.eel.is/c++draft/cstdlib.syn#header:%3Ccstdlib%3E
[1] https://cgit.freebsd.org/src/tree/contrib/llvm-project/libcxx/include/cstdlib
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