Add UEFI target support

Author: Xiaoyu Lu

build.rs

@@ -235,6 +235,13 @@ const ASM_TARGETS: &[AsmTarget] = &[
         asm_extension: "S",
         preassemble: true,
     },
+    AsmTarget {
+        oss: &[UEFI],
+        arch: "x86_64",
+        perlasm_format: "nasm",
+        asm_extension: "asm",
+        preassemble: true,
+    },
 ];
 
 struct AsmTarget {
@@ -279,6 +286,8 @@ const MACOS_ABI: &[&str] = &["ios", "macos"];
 
 const WINDOWS: &str = "windows";
 
+const UEFI: &str = "uefi";
+
 /// Read an environment variable and tell Cargo that we depend on it.
 ///
 /// This needs to be used for any environment variable that isn't a standard
@@ -381,8 +390,9 @@ fn pregenerate_asm_main() {
         perlasm(&perlasm_src_dsts, asm_target);
 
         if asm_target.preassemble {
-            // Preassembly is currently only done for Windows targets.
-            assert_eq!(&asm_target.oss, &[WINDOWS]);
+            // Preassembly is currently done for Windows and UEFI targets.
+            assert!(asm_target.oss.contains(&WINDOWS) || asm_target.oss.contains(&UEFI));
+
             let os = WINDOWS;
 
             let srcs = asm_srcs(perlasm_src_dsts);
@@ -460,7 +470,7 @@ fn build_c_code(
 
         // For Windows we also pregenerate the object files for non-Git builds so
         // the user doesn't need to install the assembler.
-        if use_pregenerated && target.os == WINDOWS {
+        if use_pregenerated && (target.os == WINDOWS || target.os == UEFI) {
             asm_srcs = asm_srcs
                 .iter()
                 .map(|src| obj_path(&pregenerated, src.as_path()))
@@ -602,6 +612,7 @@ fn cc(file: &Path, ext: &str, target: &Target, include_dir: &Path, out_file: &Pa
         && target.os != "redox"
         && target.os != "windows"
         && target.arch != "wasm32"
+        && target.os != "uefi"
     {
         let _ = c.flag("-fstack-protector");
     }
@@ -642,6 +653,13 @@ fn cc(file: &Path, ext: &str, target: &Target, include_dir: &Path, out_file: &Pa
         }
     }
 
+    // UEFI is a baremental freestanding environment without stdlib.
+    if target.os == "uefi" && target.arch == "x86_64" {
+        let _ = c.flag("-nostdlibinc");
+        let _ = c.define("RING_CORE_NOSTDLIBINC", "1");
+        let _ = c.flag("-ffreestanding");
+    }
+
     if target.force_warnings_into_errors {
         c.warnings_into_errors(true);
     }