Commit cd03a0a153aae3e0450b7878b67906fb41521d13 | zig

author	Alex Rønne Petersen <alex@alexrp.com> 2025-06-02 19:02:08+02:00
committer	Alex Rønne Petersen <alex@alexrp.com> 2025-06-04 05:04:29+02:00
log	cd03a0a153aae3e0450b7878b67906fb41521d13
tree	81aabde76e990bc4e26f9aa3df0db6a8a983f424
parent	826e1c30ba81884e1a8fad8664b3da17953d89d1

compiler: Don't link ucrtbased.dll when targeting *-windows-msvc in Debug mode.

Linking it by default means that we produce binaries that, effectively, only run
on systems which have the Windows SDK installed because ucrtbased.dll is not
redistributable, and the Windows SDK is what actually installs ucrtbased.dll
into %SYSTEM32%. The resulting binaries also can't run under Wine because Wine
does not provide ucrtbased.dll.

It is also inconsistent with our behavior for *-windows-gnu where we always link
ucrtbase.dll. See #23983, #24019, and #24053 for more details.

So just use ucrtbase.dll regardless of mode. With this change, we can also drop
the implicit definition of the _DEBUG macro in zig cc, which has in some cases
been problematic for users.

Users who want to opt into the old behavior can do so, both for *-windows-msvc
and *-windows-gnu, by explicitly passing -lucrtbased and -D_DEBUG. We might
consider adding a more ergonomic flag like -fdebug-crt to the zig build-* family
of commands in the future.

Closes #24052.

2 files changed, 10 insertions(+), 18 deletions(-)

src
- Compilation.zig
- link
  - Coff.zig

src/Compilation.zig+2-6

 @@ -5904,8 +5904,7 @@ fn updateWin32Resource(comp: *Compilation, win32_resource: *Win32Resource, win32
         // them being defined matches the behavior of how MSVC calls rc.exe which is the more
         // relevant behavior in this case.
         switch (rc_src.owner.optimize_mode) {
-            .Debug => try argv.append("-D_DEBUG"),
+            .Debug, .ReleaseSafe => {},
-            .ReleaseSafe => {},
             .ReleaseFast, .ReleaseSmall => try argv.append("-DNDEBUG"),
         }
         try argv.appendSlice(rc_src.extra_flags);
 @@ -6260,10 +6259,7 @@ pub fn addCCArgs(
         // LLVM IR files don't support these flags.
         if (ext != .ll and ext != .bc) {
             switch (mod.optimize_mode) {
-                .Debug => {
+                .Debug => {},
-                    // windows c runtime requires -D_DEBUG if using debug libraries
-                    try argv.append("-D_DEBUG");
-                },
                 .ReleaseSafe => {
                     try argv.append("-D_FORTIFY_SOURCE=2");
                 },

src/link/Coff.zig+8-12

 @@ -2113,21 +2113,17 @@ fn linkWithLLD(coff: *Coff, arena: Allocator, tid: Zcu.PerThread.Id, prog_node:
                         try argv.append(try comp.crtFileAsString(arena, "libmingw32.lib"));
                     } else {
+                        try argv.append(switch (comp.config.link_mode) {
+                            .static => "libcmt.lib",
+                            .dynamic => "msvcrt.lib",
+                        });
                         const lib_str = switch (comp.config.link_mode) {
-                            .dynamic => "",
                             .static => "lib",
+                            .dynamic => "",
                         };
-                        const d_str = switch (optimize_mode) {
+                        try argv.append(try allocPrint(arena, "{s}vcruntime.lib", .{lib_str}));
-                            .Debug => "d",
+                        try argv.append(try allocPrint(arena, "{s}ucrt.lib", .{lib_str}));
-                            else => "",
-                        };
-                        switch (comp.config.link_mode) {
-                            .static => try argv.append(try allocPrint(arena, "libcmt{s}.lib", .{d_str})),
-                            .dynamic => try argv.append(try allocPrint(arena, "msvcrt{s}.lib", .{d_str})),
-                        }
-                        try argv.append(try allocPrint(arena, "{s}vcruntime{s}.lib", .{ lib_str, d_str }));
-                        try argv.append(try allocPrint(arena, "{s}ucrt{s}.lib", .{ lib_str, d_str }));
                         //Visual C++ 2015 Conformance Changes
                         //https://msdn.microsoft.com/en-us/library/bb531344.aspx