[zig cc] libresolv symbol not found under linux

[michaelortmann]

Zig Version

0.15.2

Steps to Reproduce and Observed Behavior

> cat test.c 
#include <resolv.h>
#include <stdio.h>
#include <string.h>

int main() {
    const char *s = "test";
    char out[sizeof s << 1];

    b64_ntop((const unsigned char *) s, strlen(s), out, sizeof out);

    printf("%s\n", out);
}
> clang -Wall test.c -o test -lresolv`
> ./test
dGVzdA==
> zig cc -Wall test.c -o test -lresolv
ld.lld: error: undefined symbol: __b64_ntop
>>> referenced by test.c:9
>>>               /home/michael/.cache/zig/o/d3eb4eae11967bfaa9bf667ce900d74b/test.o:(main)

Under FreeBSD it is working fine without -lresolv

Expected Behavior

I expect zig cc to resolve symbols (in system libc/libresolv/zigs musl libc)

[michaelortmann]

(and yes, the sizeof s i taking the size of the pointer, but it doesnt matter for this example)

[alexrp]

What kind of system are you on? You haven't passed a cross -target flag, so it'll be a native build.

[michaelortmann]

Arch Linux (glibc 2.42). I am not trying to cross compile.
What i meant was, when i try to compile it native under FreeBSD it works,
but when i try to compile it native under Linux (glibc) it doesnt.

[alexrp]

The problem is that isLibCLibName considers resolv to be a libc library name:

zig/lib/std/zig/target.zig

Lines 342 to 355 in a6d444c

	if (target.abi.isGnu() or target.abi.isMusl()) {
	if (eqlIgnoreCase(ignore_case, name, "m"))
	return true;
	if (eqlIgnoreCase(ignore_case, name, "rt"))
	return true;
	if (eqlIgnoreCase(ignore_case, name, "pthread"))
	return true;
	if (eqlIgnoreCase(ignore_case, name, "util"))
	return true;
	if (eqlIgnoreCase(ignore_case, name, "resolv"))
	return true;
	if (eqlIgnoreCase(ignore_case, name, "dl"))
	return true;
	}

So it gets removed from the linker inputs on the assumption that it will be specially handled by the compiler:

zig/src/main.zig

Lines 3832 to 3839 in a6d444c

	for (create_module.cli_link_inputs.items) |cli_link_input| switch (cli_link_input) {
	.name_query => |nq| {
	const lib_name = nq.name;
	if (std.zig.target.isLibCLibName(target, lib_name)) {
	create_module.opts.link_libc = true;
	continue;
	}

And it does indeed get handled when cross-compiling:

zig/src/libs/glibc.zig

Lines 37 to 47 in a6d444c

	// The order of the elements in this array defines the linking order.
	pub const libs = [_]Lib{
	.{ .name = "m", .sover = 6 },
	.{ .name = "c", .sover = 6 },
	.{ .name = "ld", .sover = 2 },
	.{ .name = "resolv", .sover = 2 },
	.{ .name = "pthread", .sover = 0, .removed_in = .{ .major = 2, .minor = 34, .patch = 0 } },
	.{ .name = "dl", .sover = 2, .removed_in = .{ .major = 2, .minor = 34, .patch = 0 } },
	.{ .name = "rt", .sover = 1, .removed_in = .{ .major = 2, .minor = 34, .patch = 0 } },
	.{ .name = "util", .sover = 1, .removed_in = .{ .major = 2, .minor = 34, .patch = 0 } },
	};

zig/src/link/Lld.zig

Lines 1210 to 1221 in a6d444c

	} else if (target.isGnuLibC()) {
	for (glibc.libs) |lib| {
	if (lib.removed_in) |rem_in| {
	if (target.os.versionRange().gnuLibCVersion().?.order(rem_in) != .lt) continue;
	}
	const lib_path = try std.fmt.allocPrint(arena, "{f}{c}lib{s}.so.{d}", .{
	comp.glibc_so_files.?.dir_path, fs.path.sep, lib.name, lib.sover,
	});
	try argv.append(lib_path);
	}
	try argv.append(try comp.crtFileAsString(arena, "libc_nonshared.a"));

But not for a native build:

zig/src/target.zig

Lines 432 to 435 in a6d444c

	.linux => switch (target.abi) {
	.android, .androideabi, .ohos, .ohoseabi => &.{ "-lm", "-lc", "-ldl" },
	else => &.{ "-lm", "-lpthread", "-lc", "-ldl", "-lrt", "-lutil" },
	},

zig/src/link/Lld.zig

Lines 1205 to 1209 in a6d444c

	if (comp.libc_installation != null) {
	const needs_grouping = link_mode == .static;
	if (needs_grouping) try argv.append("--start-group");
	try argv.appendSlice(target_util.libcFullLinkFlags(target));
	if (needs_grouping) try argv.append("--end-group");

I'll need to do some thinking about how to handle this. The easy fix is of course just to add -lresolv to libcFullLinkFlags, but maybe we need to rethink this stuff.