Update wasi-libc to d03829489904d38c624f6de9983190f1e5e7c9c5

[jedisct1]

Most notable improvements include realpath and stubs for statvfs, chmod, etc.

Other changes are for WASI 0.2 which is going to be painful to support since 3rd party tools written in Rust may become necessary in addition to LLVM (WebAssembly/wasi-sdk#402)

[jedisct1]

This also removes junk we were shipping but irrelevant to webassembly.

[lin72h]

10KLoc reduce, feel so good

[jedisct1]

Added the wasi-libc libdl shim, so that tools such as py2wasm can use zig cc.

[andrewrk]

man. wasi-libc kinda sucks. how about we provide libc via zig code instead?

[jedisct1]

wasi-libc is horrible. And it's getting worse with the wasi preview 2 bits.

But rewriting it in Zig would be a lot of work.

[alexrp]

With the libdl shim, isn't this wrong?

[jedisct1]

That would pick the wrong libdl.

[alexrp]

I see, we have a special case for WASI here:

zig/src/main.zig

Lines 3766 to 3821 in c96f9a0

	for (create_module.system_libs.keys(), create_module.system_libs.values()) |lib_name, info| {
	if (target.is_libc_lib_name(lib_name)) {
	create_module.opts.link_libc = true;
	continue;
	}
	if (target.is_libcpp_lib_name(lib_name)) {
	create_module.opts.link_libcpp = true;
	continue;
	}
	switch (target_util.classifyCompilerRtLibName(target, lib_name)) {
	.none => {},
	.only_libunwind, .both => {
	create_module.opts.link_libunwind = true;
	continue;
	},
	.only_compiler_rt => {
	warn("ignoring superfluous library '{s}': this dependency is fulfilled instead by compiler-rt which zig unconditionally provides", .{lib_name});
	continue;
	},
	}
	if (target.isMinGW()) {
	const exists = mingw.libExists(arena, target, zig_lib_directory, lib_name) catch |err| {
	fatal("failed to check zig installation for DLL import libs: {s}", .{
	@errorName(err),
	});
	};
	if (exists) {
	try create_module.resolved_system_libs.append(arena, .{
	.name = lib_name,
	.lib = .{
	.needed = true,
	.weak = false,
	.path = null,
	},
	});
	continue;
	}
	}
	if (fs.path.isAbsolute(lib_name)) {
	fatal("cannot use absolute path as a system library: {s}", .{lib_name});
	}
	if (target.os.tag == .wasi) {
	if (wasi_libc.getEmulatedLibCRTFile(lib_name)) |crt_file| {
	try create_module.wasi_emulated_libs.append(arena, crt_file);
	continue;
	}
	}
	try external_system_libs.append(arena, .{
	.name = lib_name,
	.info = info,
	});
	}

Still seems not good that is_libc_lib_name() returns false for these since all other parts of the codebase (like std.Build) will get the wrong answer.

Can't we just make is_libc_lib_name() do the right thing, and move the special case in main.zig so it happens before the is_libc_lib_name() check?

[jedisct1]

I don't know if this is worth too much changes. The WASI dl library is just an awful hack to hopefully make some apps compile out of the box. But it only contains stub functions. None of them work.

[alexrp]

Well the above should apply to the other emulated libraries as well - e.g. wasi-emulated-clocks, which seems a fair bit more useful than the silly dl shim. is_libc_lib_name() will currently say that wasi-emulated-clocks isn't a libc library name, misleading std.Build. This is why I'm suggesting we just make is_libc_lib_name() do what it's supposed to do and then move the code block in main.zig up a bit. Then, going forward, adding new library names will work just like it does for the other libcs we provide.