Fix cross compilation with clang-cl

1 files changed, 49 insertions, 19 deletions

diff --git a/build.rs b/build.rs
index 2557120..8e06376 100644
--- a/build.rs
+++ b/build.rs
@@ -43,6 +43,23 @@ fn is_x86_64() -> bool {
     target_components()[0] == "x86_64"
 }
 
+fn is_windows_target() -> bool {
+    env::var("CARGO_CFG_TARGET_OS").unwrap() == "windows"
+}
+
+fn use_msvc_asm() -> bool {
+    // cc assumes if it is passed .asm and targetting MSVC that it can use the
+    // Microsoft assemblers, which isn't true when we're not on a Windows
+    // host, but are cross-compiling with clang-cl, so we explicitly check if
+    // we're on a Windows host (with the assumption they'll have the MSVC
+    // toolchain installed if they are, though that's not necessarily true)
+    if env::var("CARGO_CFG_TARGET_ENV").unwrap_or_default() == "gnu" {
+        false
+    } else {
+        env::var("HOST").unwrap_or_default().contains("-windows-")
+    }
+}
+
 fn is_x86_32() -> bool {
     let arch = &target_components()[0];
     arch == "i386" || arch == "i586" || arch == "i686"
@@ -172,14 +189,16 @@ fn build_sse2_sse41_avx2_assembly() {
     println!("cargo:rustc-cfg=blake3_sse41_ffi");
     println!("cargo:rustc-cfg=blake3_avx2_ffi");
     let mut build = new_build();
-    if is_windows_msvc() {
-        build.file("c/blake3_sse2_x86-64_windows_msvc.asm");
-        build.file("c/blake3_sse41_x86-64_windows_msvc.asm");
-        build.file("c/blake3_avx2_x86-64_windows_msvc.asm");
-    } else if is_windows_gnu() {
-        build.file("c/blake3_sse2_x86-64_windows_gnu.S");
-        build.file("c/blake3_sse41_x86-64_windows_gnu.S");
-        build.file("c/blake3_avx2_x86-64_windows_gnu.S");
+    if is_windows_target() {
+        if use_msvc_asm() {
+            build.file("c/blake3_sse2_x86-64_windows_msvc.asm");
+            build.file("c/blake3_sse41_x86-64_windows_msvc.asm");
+            build.file("c/blake3_avx2_x86-64_windows_msvc.asm");
+        } else {
+            build.file("c/blake3_sse2_x86-64_windows_gnu.S");
+            build.file("c/blake3_sse41_x86-64_windows_gnu.S");
+            build.file("c/blake3_avx2_x86-64_windows_gnu.S");
+        }
     } else {
         // All non-Windows implementations are assumed to support
         // Linux-style assembly. These files do contain a small
@@ -216,19 +235,21 @@ fn build_avx512_assembly() {
     assert!(is_x86_64());
     println!("cargo:rustc-cfg=blake3_avx512_ffi");
     let mut build = new_build();
-    if is_windows_msvc() {
-        build.file("c/blake3_avx512_x86-64_windows_msvc.asm");
-    } else {
-        if is_windows_gnu() {
-            build.file("c/blake3_avx512_x86-64_windows_gnu.S");
+    let mut is_msvc = false;
+    if is_windows_target() {
+        if use_msvc_asm() {
+            build.file("c/blake3_avx512_x86-64_windows_msvc.asm");
+            is_msvc = true;
         } else {
-            // All non-Windows implementations are assumed to support Linux-style
-            // assembly. These files do contain a small explicit workaround for
-            // macOS also.
-            build.file("c/blake3_avx512_x86-64_unix.S");
+            build.file("c/blake3_avx512_x86-64_windows_gnu.S");
         }
-        // Older versions of Clang require these flags, even for assembly. See
-        // https://github.com/BLAKE3-team/BLAKE3/issues/79.
+    } else {
+        build.file("c/blake3_avx512_x86-64_unix.S");
+    }
+
+    // Older versions of Clang require these flags, even for assembly. See
+    // https://github.com/BLAKE3-team/BLAKE3/issues/79.
+    if !is_msvc {
         build.flag("-mavx512f");
         build.flag("-mavx512vl");
     }
@@ -321,5 +342,14 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         );
     }
 
+    // When compiling with clang-cl for windows, it adds .asm files to the root
+    // which we need to delete so cargo doesn't get angry
+    if is_windows_target() && !use_msvc_asm() {
+        let _ = std::fs::remove_file("blake3_avx2_x86-64_windows_gnu.asm");
+        let _ = std::fs::remove_file("blake3_avx512_x86-64_windows_gnu.asm");
+        let _ = std::fs::remove_file("blake3_sse2_x86-64_windows_gnu.asm");
+        let _ = std::fs::remove_file("blake3_sse41_x86-64_windows_gnu.asm");
+    }
+
     Ok(())
 }