1 files changed, 18 insertions, 2 deletions
diff --git a/vendor/compiler_builtins/build.rs b/vendor/compiler_builtins/build.rs
index 73952bb9f..3f5dbd3ab 100644
--- a/vendor/compiler_builtins/build.rs
+++ b/vendor/compiler_builtins/build.rs
@@ -98,7 +98,7 @@ mod c {
 
     use std::collections::{BTreeMap, HashSet};
     use std::env;
-    use std::fs::File;
+    use std::fs::{self, File};
     use std::io::Write;
     use std::path::{Path, PathBuf};
 
@@ -190,6 +190,21 @@ mod c {
             cfg.define("VISIBILITY_HIDDEN", None);
         }
 
+        // int_util.c tries to include stdlib.h if `_WIN32` is defined,
+        // which it is when compiling UEFI targets with clang. This is
+        // at odds with compiling with `-ffreestanding`, as the header
+        // may be incompatible or not present. Create a minimal stub
+        // header to use instead.
+        if target_os == "uefi" {
+            let out_dir = PathBuf::from(env::var("OUT_DIR").unwrap());
+            let include_dir = out_dir.join("include");
+            if !include_dir.exists() {
+                fs::create_dir(&include_dir).unwrap();
+            }
+            fs::write(include_dir.join("stdlib.h"), "#include <stddef.h>").unwrap();
+            cfg.flag(&format!("-I{}", include_dir.to_str().unwrap()));
+        }
+
         let mut sources = Sources::new();
         sources.extend(&[
             ("__absvdi2", "absvdi2.c"),
@@ -465,7 +480,8 @@ mod c {
         }
 
         // Remove the assembly implementations that won't compile for the target
-        if llvm_target[0] == "thumbv6m" || llvm_target[0] == "thumbv8m.base" {
+        if llvm_target[0] == "thumbv6m" || llvm_target[0] == "thumbv8m.base" || target_os == "uefi"
+        {
             let mut to_remove = Vec::new();
             for (k, v) in sources.map.iter() {
                 if v.ends_with(".S") {