zig build-lib does not allow linking to a C program

[perillo]

In the Zig Language Reference there are two example of linking a Zig library to a C program in the "Exporting a C Library" and "Mixing Object Files" sections. Both examples fail.

These are the issues I found:

• [x] Static linking using a C compiler fails

  Using the mathtest.zig example

  zig build-lib -femit-h mathtest.zig
  
  gcc -o test -static -I $(zig env | jq -r .lib_dir) test.c -L . -lmathtest
  ./test

  /usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `debug.readElfDebugInfo':
  /home/manlio/.local/share/sdk/zig/master/lib/std/debug.zig:939: undefined reference to `__zig_probe_stack'
  /usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `fs.Dir.openFile':
  /home/manlio/.local/share/sdk/zig/master/lib/std/fs.zig:1099: undefined reference to `__zig_probe_stack'
  /usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `debug.printLineFromFileAnyOs__anon_5459':
  /home/manlio/.local/share/sdk/zig/master/lib/std/debug.zig:1164: undefined reference to `__zig_probe_stack'
  /usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `dwarf.DwarfInfo.getLineNumberInfo':
  /home/manlio/.local/share/sdk/zig/master/lib/std/dwarf.zig:1090: undefined reference to `__zig_probe_stack'
  /usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `debug.panicExtra__anon_5748':
  /home/manlio/.local/share/sdk/zig/master/lib/std/debug.zig:297: undefined reference to `__zig_probe_stack'
  /usr/bin/ld: ./libmathtest.a(./libmathtest.a.o):/home/manlio/.local/share/sdk/zig/master/lib/std/debug.zig:297: more undefined references to `__zig_probe_stack' follow
  collect2: error: ld returned 1 exit status

  I'm not sure if this works as expected. When using zig build the generated executable is dynamically linked.

  See #14099.

• [ ] Setting LibExeObjStep.emit_h to true, does not emit the header file a second time when the header file is removed

  const Builder = @import("std").build.Builder;
  
  pub fn build(b: *Builder) void {
      const lib = b.addSharedLibrary("mathtest", "mathtest.zig", b.version(1, 0, 0));
      lib.emit_h = true;
  
      const exe = b.addExecutable("test", null);
      exe.addCSourceFile("test.c", &[_][]const u8{"-std=c99"});
      exe.linkLibrary(lib);
      exe.linkSystemLibrary("c");
  
      b.default_step.dependOn(&exe.step);
  
      const run_cmd = exe.run();
  
      const test_step = b.step("test", "Test the program");
      test_step.dependOn(&run_cmd.step);
  }

  When mathtest.h does not exists, zig build will create it, but if I remove the file, zig build will not create it again.

  The reason is that the build system always enables caching, but the generated header file is not cached in the artifact directory.

  See #14606.

• [ ] zig build should automatically include zig.h header when emit_h is set to true.

  When an executable links a library with emit_h set to true, the build system should automatically append the path to zig_dir to exe.include_dirs.

  See #14576.

Thanks.

[kassane]

In the Zig Language Reference there are two example of linking a Zig library to a C program in the "Exporting a C Library" and "Mixing Object Files" sections. Both examples fail.

These are the issues I found:

Static linking using a C compiler fails

Using the mathtest.zig example

zig build-lib -femit-h mathtest.zig

gcc -o test -static -I $(zig env | jq -r .lib_dir) test.c -L . -lmathtest
./test

/usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `debug.readElfDebugInfo':
/home/manlio/.local/share/sdk/zig/master/lib/std/debug.zig:939: undefined reference to `__zig_probe_stack'
/usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `fs.Dir.openFile':
/home/manlio/.local/share/sdk/zig/master/lib/std/fs.zig:1099: undefined reference to `__zig_probe_stack'
/usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `debug.printLineFromFileAnyOs__anon_5459':
/home/manlio/.local/share/sdk/zig/master/lib/std/debug.zig:1164: undefined reference to `__zig_probe_stack'
/usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `dwarf.DwarfInfo.getLineNumberInfo':
/home/manlio/.local/share/sdk/zig/master/lib/std/dwarf.zig:1090: undefined reference to `__zig_probe_stack'
/usr/bin/ld: ./libmathtest.a(./libmathtest.a.o): in function `debug.panicExtra__anon_5748':
/home/manlio/.local/share/sdk/zig/master/lib/std/debug.zig:297: undefined reference to `__zig_probe_stack'
/usr/bin/ld: ./libmathtest.a(./libmathtest.a.o):/home/manlio/.local/share/sdk/zig/master/lib/std/debug.zig:297: more undefined references to `__zig_probe_stack' follow
collect2: error: ld returned 1 exit status

You have built the library in debug mode. If you build in releaseFast or small mode the error will not occur, or add -fcompiler-rt in build-lib. https://github.com/ziglang/zig/issues/6817#issuecomment-736129115

[perillo]

You have built the library in debug mode. If you build in releaseFast or small mode the error will not occur, or add -fcompiler-rt in build-lib. #6817 (comment)

Thanks.

[kubkon]

Fixed in https://github.com/ziglang/zig/pull/14644

[kubkon]

Scratch my last comment. This issue goes away if you explicitly pass -fcompiler-rt. Whether this should be automatic I'll leave to @andrewrk, so reopening.

[perillo]

Scratch my last comment. This issue goes away if you explicitly pass -fcompiler-rt. Whether this should be automatic I'll leave to @andrewrk, so reopening.

I converted the 3 different issues into separate tasks.

I'm not sure about the last task, since the (currently disabled) test-gen-h test suite expects clean C code: https://github.com/ziglang/zig/blob/master/test/gen_h.zig. A problem with this approach is name collision.

[owend]

Hello! With the latest versions of zig on MacOS (I tried version 0.10 and 0.11 and 0.12 and compiled from main/HEAD) this example now segfaults. Instead of opening a new bug I thought I would just add it here.

zig build-lib -femit-h mathtest.zig

➞  zig build-lib -femit-h  mathtest.zig
AST Lowering [519] target/aarch64.zig... thread 604505 panic: reached unreachable code
/Projects/zig/lib/std/debug.zig:342:14: 0x109fa4c7c in assert (zig)
    if (!ok) unreachable; // assertion failure
/Projects/zig/src/Module.zig:5343:19: 0x10a08705c in allocateNewDecl (zig)
            assert(@intFromEnum(decl_index) == mod_emit_h.allocated_emit_h.len);
/Projects/zig/src/Module.zig:3912:51: 0x10a22b0fc in semaFile (zig)
    const new_decl_index = try mod.allocateNewDecl(new_namespace_index, 0, null);
/Projects/zig/src/Module.zig:3888:24: 0x10a22ae81 in semaPkg (zig)
    return mod.semaFile(file);
/Projects/zig/src/Compilation.zig:3323:27: 0x10a25b19d in processOneJob (zig)
            module.semaPkg(pkg) catch |err| switch (err) {
/Projects/zig/src/Compilation.zig:3151:30: 0x10a0cddfe in performAllTheWork (zig)
            try processOneJob(comp, work_item, main_progress_node);
/Projects/zig/src/Compilation.zig:2058:31: 0x10a0c9929 in update (zig)
    try comp.performAllTheWork(main_progress_node);
/Projects/zig/src/main.zig:4098:24: 0x10a0fa161 in updateModule (zig)
        try comp.update(main_progress_node);

I added a debug print statement right before this block where the assertion is shown in Module.zig

        if (@intFromEnum(decl_index) >= mod_emit_h.allocated_emit_h.len) {
            try mod_emit_h.allocated_emit_h.append(gpa, .{});
            assert(@intFromEnum(decl_index) == mod_emit_h.allocated_emit_h.len);
        }

allocated_emit_h = segmented_list.SegmentedList(Module.EmitH,0) decl_index = Module.Decl.Index(0) allocated_emit_h.len = 0

It looks like the situation is (pseudo-code)

if 0 >= 0
    list.append
    assert 0 == 1

If the append succeeds, the assert always fails.

[owend]

Every once in a while I re-test this, and now the error message has changed:

thread 17539456 panic: regressed compiler feature: emit-h should hook into updateExports, not decl analysis, which is too early to know about @export calls

It looks like this check was added here: https://github.com/ziglang/zig/commit/00da182e68