Adds wait4/wait3 to libc build, fixes #19188

[Mai-Lapyst]

Fixes missing wait4 and wait3 functions by adding the relevant source files from the musl libc to the build process of the libc.

[kripken]

Do these functions work in our environment? They are related to process management, which we have only minimal support for.

[Mai-Lapyst]

Do these functions work in our environment? They are related to process management, which we have only minimal support for.

They "work" the same way as waitpid works, which is currently implemented. It internally calls __syscall_wait4 which then gets a warning with wasmtime for example, but atleast the binary now compiles which previously it wouldn't (see #19188). This is annoying when trying to compile code that relies on the wait4 symbol to be present.

[sbc100]

Hm,.. but I don't see __syscall_wait4 defined anywhere, so I would have though this would still be a linker error.

Presumably you should add __syscall_wait4 to system/lib/libc/emscripten_syscall_stubs.c and then also add a test to confirm that linking against wait4 and wait3 doesn't fail?

[sbc100]

Oh, sorry I see that we do already have stub for __syscall_wait4.. its was just hard to grep for:

emscripten/system/lib/libc/emscripten_syscall_stubs.c

Line 259 in 14cb3a3

UNIMPLEMENTED(wait4,(int pid, intptr_t wstatus, int options, int rusage))

In that case I think all we need is a test for these new functions (and maybe waitpid while you are at it). Maybe add a new test/other/test_syscall_stubs.c?

[Mai-Lapyst]

Oh, sorry I see that we do already have stub for __syscall_wait4.. its was just hard to grep for:

emscripten/system/lib/libc/emscripten_syscall_stubs.c

Line 259 in 14cb3a3

UNIMPLEMENTED(wait4,(int pid, intptr_t wstatus, int options, int rusage))

In that case I think all we need is a test for these new functions (and maybe waitpid while you are at it). Maybe add a new test/other/test_syscall_stubs.c?

Have added it like requested. Also manually verified that it fails prior to this change, and succeeds after applying it.