[libc][POSIX] provide sys/un.h

[nickdesaulniers]

building clang against llvm-libc fails with 'sys/un.h' file not found because lib/Support/raw_socket_stream.cpp uses sockaddr_un which should be provided by that header.

[llvmbot]

@llvm/issue-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

building clang against llvm-libc fails with `'sys/un.h' file not found` because lib/Support/raw_socket_stream.cpp uses `sockaddr_un` which should be provided by that header.

[nickdesaulniers]

This header should be straightforward to implement; by POSIX (and the corresponding usage in llvm), it only need define struct sockaddr_un. POSIX says it only needs to have 2 fields. We already define sa_family_t in libc/include/llvm-libc-types/sa_family_t.h, so one would need to:

1. create a new file libc/include/llvm-libc-types/sockaddr_un.h
2. in the new header #include <llvm-libc-types/sa_family_t.h>.
3. add an entry for that in libc/include/llvm-libc-types/CMakeLists.txt and make sure to express the dependency on .sa_family_t.
4. Create libc/include/sys/{un.h.def|un.yaml} and fill those out.
5. modify libc/include/CMakeLists.txt to add an entry for those.
6. add an anchor to the dependency in libc/config/linux/x86_64/headers.txt so that the new header gets generated during build time.
7. add an entry to libc/docs/headers/index.rst

Tagging as a simpler beginner bug.

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

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If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Nick Desaulniers (nickdesaulniers)

building clang against llvm-libc fails with `'sys/un.h' file not found` because lib/Support/raw_socket_stream.cpp uses `sockaddr_un` which should be provided by that header.

[nickdesaulniers]

Oh, the size. What value to use?

POSIX says:

where size shall be an implementation-provided constant size of at least 92 bytes.

A quick survey:

• glibc: 108
• bionic: just includes <linux/un.h> which uses UNIX_PATH_MAX which is defined to 108.
• musl: 108

Interesting. I wonder if that size differs for either windows or darwin?

#include <sys/un.h>
struct sockaddr_un x;
static_assert(sizeof(x.sun_path) == 0, "");

@michaelrj-google reports that fails on macos with sizeof 104...so sockaddr_un likely does have to be a platform specific type.

---

In that case, then I think we can stick with some ifdef'ery in the to-be-created libc/include/llvm-libc-types/sockaddr_un.h at least for the size.

[get-state]

I don't mind doing this, will try next week.

[nickdesaulniers]

Thanks! Let us know if you get stuck or have any questions.