Win32 dll in rust

win32/dll/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "dll"
+version = "0.1.0"
+build = "build.rs"
+edition = "2021"
+
+[workspace]
+resolver = "2"
+
+[[example]]
+name = "advapi32"
+crate-type = ["cdylib"]
+path = "advapi32.rs"
+
+[lib]
+path = "lib.rs"
+
+[profile.release]
+panic = "abort"
+# Disabling debug appears to do nothing on Windows :(
+debug = false
+strip = true

win32/dll/advapi32.rs

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+#![no_std]
+#![no_main]
+
+#[panic_handler]
+fn panic(_: &::core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[link(
+    name = "retrowin32",
+    kind = "raw-dylib",
+    import_name_type = "undecorated"
+)]
+extern "stdcall" {
+    fn retrowin32_syscall();
+}
+
+#[no_mangle]
+pub unsafe extern "stdcall" fn RegCloseKey(_: u32) {
+    retrowin32_syscall();
+}
+
+#[no_mangle]
+pub unsafe extern "stdcall" fn RegOpenKey(_: u32) {
+    retrowin32_syscall();
+}
+
+// Have to wrap the pointers in a struct to impl Sync.
+// Have to impl Sync to use in a static.
+// The other option is a "static mut" but that creates a .data section we don't otherwise need.
+#[repr(transparent)]
+pub struct VTableEntry(*const fn());
+unsafe impl Sync for VTableEntry {}
+
+#[no_mangle]
+pub static vtab: [VTableEntry; 4] = [
+    VTableEntry(core::ptr::null()),
+    VTableEntry(RegCloseKey as _),
+    VTableEntry(core::ptr::null()),
+    VTableEntry(RegOpenKey as _),
+];
+
+// core::arch::global_asm!(
+//     ".globl _IDirectSound",
+//     "_IDirectSound:",
+//     ".long _RegCloseKey",
+//     ".long 0",
+// );

win32/dll/build.rs

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+#[cfg(target_family = "unix")]
+fn main() {
+    println!("cargo:rerun-if-env-changed=XWIN");
+    if let Ok(xwin) = std::env::var("XWIN") {
+        for dir in ["crt/lib/x86", "sdk/lib/ucrt/x86", "sdk/lib/um/x86"] {
+            println!(r"cargo:rustc-link-search={xwin}/{dir}");
+        }
+    }
+
+    println!("cargo::rustc-link-arg=/Brepro");
+    println!("cargo::rustc-link-arg=/noentry");
+    println!("cargo::rustc-link-arg=/nodefaultlib");
+    // This doesn't help, we need -Zmerge-functions=disabled
+    // println!("cargo::rustc-link-arg=/OPT:NOICF");
+    // This doesn't disable debug info, turns out /Brepro causes it
+    // println!("cargo::rustc-link-arg=/DEBUG:NONE");
+}
+
+#[cfg(target_family = "windows")]
+fn main() {}

win32/dll/lib.rs

@@ -0,0 +1 @@
+