Merge pull request 'Export wrapper around Zig DllMain function when linking libc + add tests' (#32179) from squeek502/zig:windows-dlls into master

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/32179
Reviewed-by: Andrew Kelley <andrew@ziglang.org>

lib/std/start.zig

@@ -23,6 +23,10 @@ comptime {
         const dll_main_crt_startup = if (builtin.abi.isGnu()) "DllMainCRTStartup" else "_DllMainCRTStartup";
         if (native_os == .windows and !builtin.link_libc and !@hasDecl(root, dll_main_crt_startup)) {
             @export(&DllMainCRTStartup, .{ .name = dll_main_crt_startup });
+        } else if (native_os == .windows and builtin.link_libc and @hasDecl(root, "DllMain")) {
+            if (!@typeInfo(@TypeOf(root.DllMain)).@"fn".calling_convention.eql(.winapi)) {
+                @export(&DllMain, .{ .name = "DllMain" });
+            }
         }
     } else if (builtin.output_mode == .Exe or @hasDecl(root, "main")) {
         if (builtin.link_libc and @hasDecl(root, "main")) {
@@ -82,12 +86,20 @@ fn DllMainCRTStartup(
     }
 
     if (@hasDecl(root, "DllMain")) {
-        return root.DllMain(hinstDLL, fdwReason, lpReserved);
+        return root.DllMain(@ptrCast(hinstDLL), fdwReason, lpReserved);
     }
 
     return .TRUE;
 }
 
+fn DllMain(
+    hinstDLL: std.os.windows.HINSTANCE,
+    fdwReason: std.os.windows.DWORD,
+    lpReserved: std.os.windows.LPVOID,
+) callconv(.winapi) std.os.windows.BOOL {
+    return root.DllMain(@ptrCast(hinstDLL), fdwReason, lpReserved);
+}
+
 fn wasm_freestanding_start() callconv(.c) void {
     // This is marked inline because for some reason LLVM in
     // release mode fails to inline it, and we want fewer call frames in stack traces.

test/standalone/windows_entry_points/build.zig

@@ -139,4 +139,75 @@ pub fn build(b: *std.Build) void {
         _ = exe.getEmittedBin();
         test_step.dependOn(&exe.step);
     }
+
+    const load_dll_exe = b.addExecutable(.{ .name = "load_dll", .root_module = b.createModule(.{
+        .root_source_file = b.path("loaddll.zig"),
+        .target = target,
+        .optimize = .Debug,
+    }) });
+
+    {
+        const dll = b.addLibrary(.{
+            .name = "zig_dllmain",
+            .linkage = .dynamic,
+            .root_module = b.createModule(.{
+                .root_source_file = b.path("dllmain.zig"),
+                .target = target,
+                .optimize = .Debug,
+            }),
+        });
+
+        const run = b.addRunArtifact(load_dll_exe);
+        run.addArtifactArg(dll);
+        run.expectStdErrEqual("hello from DllMain");
+        run.expectStdOutEqual("");
+        run.expectExitCode(0);
+        run.skip_foreign_checks = true;
+
+        test_step.dependOn(&run.step);
+    }
+
+    {
+        const dll = b.addLibrary(.{
+            .name = "zig_dllmain_link_libc",
+            .linkage = .dynamic,
+            .root_module = b.createModule(.{
+                .root_source_file = b.path("dllmain.zig"),
+                .target = target,
+                .optimize = .Debug,
+                .link_libc = true,
+            }),
+        });
+
+        const run = b.addRunArtifact(load_dll_exe);
+        run.addArtifactArg(dll);
+        run.expectStdErrEqual("hello from DllMain");
+        run.expectStdOutEqual("");
+        run.expectExitCode(0);
+        run.skip_foreign_checks = true;
+
+        test_step.dependOn(&run.step);
+    }
+
+    {
+        const dll = b.addLibrary(.{
+            .name = "c_dllmain",
+            .linkage = .dynamic,
+            .root_module = b.createModule(.{
+                .target = target,
+                .optimize = .Debug,
+                .link_libc = true,
+            }),
+        });
+        dll.root_module.addCSourceFile(.{ .file = b.path("dllmain.c") });
+
+        const run = b.addRunArtifact(load_dll_exe);
+        run.addArtifactArg(dll);
+        run.expectStdErrEqual("hello from DllMain");
+        run.expectStdOutEqual("");
+        run.expectExitCode(0);
+        run.skip_foreign_checks = true;
+
+        test_step.dependOn(&run.step);
+    }
 }

test/standalone/windows_entry_points/dllmain.c

@@ -0,0 +1,9 @@
+#include <windows.h>
+#include <stdio.h>
+
+BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) {
+    if (fdwReason == DLL_PROCESS_ATTACH) {
+        fprintf(stderr, "hello from DllMain");
+    }
+    return TRUE;
+}

test/standalone/windows_entry_points/dllmain.zig

@@ -0,0 +1,18 @@
+const std = @import("std");
+const windows = std.os.windows;
+
+const DLL_PROCESS_ATTACH = 1;
+
+pub fn DllMain(
+    hinstDLL: windows.HINSTANCE,
+    fdwReason: windows.DWORD,
+    lpReserved: windows.LPVOID,
+) windows.BOOL {
+    _ = hinstDLL;
+    _ = lpReserved;
+    switch (fdwReason) {
+        DLL_PROCESS_ATTACH => std.debug.print("hello from DllMain", .{}),
+        else => {},
+    }
+    return .TRUE;
+}

test/standalone/windows_entry_points/loaddll.zig

@@ -0,0 +1,13 @@
+const std = @import("std");
+const windows = std.os.windows;
+
+extern "kernel32" fn LoadLibraryW(windows.LPCWSTR) callconv(.winapi) ?windows.HMODULE;
+
+pub fn main(init: std.process.Init) !void {
+    const arena = init.arena.allocator();
+    const args = try init.minimal.args.toSlice(arena);
+    if (args.len < 2) return error.NoDllPathSpecified;
+    const dll_path = args[1];
+    const dll_path_w = try std.unicode.wtf8ToWtf16LeAllocZ(arena, dll_path);
+    _ = LoadLibraryW(dll_path_w) orelse return error.FailedToLoadDll;
+}