diff --git a/src/Cargo.lock b/src/Cargo.lock
index e257f1d7..1360da5e 100644
--- a/src/Cargo.lock
+++ b/src/Cargo.lock
@@ -430,6 +430,7 @@ dependencies = [
 name = "szl"
 version = "0.1.0"
 dependencies = [
+ "cc",
  "cstr_core",
  "libboard_zynq",
  "libcortex_a9",
diff --git a/src/libc/build.rs b/src/libc/build.rs
index e7492b58..43ab8e64 100644
--- a/src/libc/build.rs
+++ b/src/libc/build.rs
@@ -7,16 +7,18 @@ mod libc {
     use std::path::Path;
     pub fn compile() {
         let cfg = &mut cc::Build::new();
+        cfg.no_default_flags(true);
+        cfg.compiler("clang");
         cfg.cpp(false);
         cfg.warnings(false);
 
-        // still have problem compiling the libunwind
         cfg.flag("-nostdlib");
         cfg.flag("-ffreestanding");
         cfg.flag("-fno-PIC");
         cfg.flag("-isystem../include");
         cfg.flag("-fno-stack-protector");
         cfg.flag("--target=armv7-none-eabihf");
+        cfg.flag("-O2");
 
         cfg.flag("-std=c99");
         cfg.flag("-fstrict-aliasing");
@@ -25,12 +27,12 @@ mod libc {
         cfg.flag("-U_FORTIFY_SOURCE");
         cfg.define("_FORTIFY_SOURCE", Some("0"));
 
-        let unwind_sources = vec![
+        let sources = vec![
             "printf.c"
         ];
 
-        let root = Path::new("../libc");
-        for src in unwind_sources {
+        let root = Path::new("./");
+        for src in sources {
             println!("cargo:rerun-if-changed={}", src);
             cfg.file(root.join("src").join(src));
         }
diff --git a/src/libunwind/build.rs b/src/libunwind/build.rs
index d907e5f1..d38a8854 100644
--- a/src/libunwind/build.rs
+++ b/src/libunwind/build.rs
@@ -1,21 +1,16 @@
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
-    llvm_libunwind::compile();
+    llvm_libunwind::compile_cpp();
+    llvm_libunwind::compile_c();
 }
 
 mod llvm_libunwind {
     use std::path::Path;
 
-    /// Compile the libunwind C/C++ source code.
-    pub fn compile() {
-        let cfg = &mut cc::Build::new();
-        cfg.cpp(true);
-        cfg.cpp_set_stdlib(None);
+    fn setup_options(cfg: &mut cc::Build) {
+        cfg.no_default_flags(true);
         cfg.warnings(false);
 
-        // libunwind expects a __LITTLE_ENDIAN__ macro to be set for LE archs, cf. #65765
-        cfg.define("__LITTLE_ENDIAN__", Some("1"));
-        // still have problem compiling the libunwind
         cfg.flag("-nostdlib");
         cfg.flag("-ffreestanding");
         cfg.flag("-fno-PIC");
@@ -23,12 +18,55 @@ mod llvm_libunwind {
         cfg.flag("-isystem../include");
         cfg.flag("-fno-stack-protector");
         cfg.flag("--target=armv7-none-eabihf");
+        cfg.flag("-O2");
+
+        cfg.flag("-std=c99");
+        cfg.flag("-fstrict-aliasing");
+        cfg.flag("-fvisibility=hidden");
+        cfg.flag_if_supported("-fvisibility-global-new-delete-hidden");
         cfg.define("_LIBUNWIND_IS_BAREMETAL", Some("1"));
         cfg.define("_LIBUNWIND_NO_HEAP", Some("1"));
         cfg.define("_LIBUNWIND_HAS_NO_THREADS", Some("1"));
         cfg.define("NDEBUG", Some("1"));
+        // libunwind expects a __LITTLE_ENDIAN__ macro to be set for LE archs, cf. #65765
+        cfg.define("__LITTLE_ENDIAN__", Some("1"));
+        cfg.define("_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS", None);
+        cfg.flag("-U_FORTIFY_SOURCE");
+        cfg.define("_FORTIFY_SOURCE", Some("0"));
+    }
 
-        cfg.flag("-std=c99");
+    pub fn compile_c() {
+        let cfg = &mut cc::Build::new();
+        setup_options(cfg);
+        cfg.compiler("clang");
+
+        let unwind_sources = vec![
+            "Unwind-sjlj.c",
+            "UnwindLevel1-gcc-ext.c",
+            "UnwindLevel1.c",
+            "UnwindRegistersRestore.S",
+            "UnwindRegistersSave.S",
+        ];
+
+        let root = Path::new("../llvm_libunwind");
+        cfg.include(root.join("include"));
+        for src in unwind_sources {
+            println!("cargo:rerun-if-changed={}", src);
+            cfg.file(root.join("src").join(src));
+        }
+
+        cfg.compile("unwind_c");
+    }
+
+    /// Compile the libunwind C/C++ source code.
+    pub fn compile_cpp() {
+        let cfg = &mut cc::Build::new();
+        setup_options(cfg);
+        cfg.compiler("clang++");
+        cfg.cpp(true);
+        cfg.cpp_set_stdlib(None);
+
+        // c++ options
         cfg.flag("-std=c++11");
         cfg.flag("-nostdinc++");
         cfg.flag("-fno-exceptions");
@@ -37,18 +75,10 @@ mod llvm_libunwind {
         cfg.flag("-funwind-tables");
         cfg.flag("-fvisibility=hidden");
         cfg.flag_if_supported("-fvisibility-global-new-delete-hidden");
-        cfg.define("_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS", None);
-        cfg.flag("-U_FORTIFY_SOURCE");
-        cfg.define("_FORTIFY_SOURCE", Some("0"));
 
         let unwind_sources = vec![
             "Unwind-EHABI.cpp",
             "Unwind-seh.cpp",
-            "Unwind-sjlj.c",
-            "UnwindLevel1-gcc-ext.c",
-            "UnwindLevel1.c",
-            "UnwindRegistersRestore.S",
-            "UnwindRegistersSave.S",
             "libunwind.cpp"
         ];
 
@@ -59,6 +89,6 @@ mod llvm_libunwind {
             cfg.file(root.join("src").join(src));
         }
 
-        cfg.compile("unwind");
+        cfg.compile("unwind_cpp");
     }
 }
diff --git a/src/szl/Cargo.toml b/src/szl/Cargo.toml
index 96689877..c97c1c3b 100644
--- a/src/szl/Cargo.toml
+++ b/src/szl/Cargo.toml
@@ -15,3 +15,6 @@ cstr_core = { version = "0.2", default-features = false }
 libboard_zynq = { git = "https://git.m-labs.hk/M-Labs/zc706.git" }
 libsupport_zynq = { git = "https://git.m-labs.hk/M-Labs/zc706.git" }
 libcortex_a9 = { git = "https://git.m-labs.hk/M-Labs/zc706.git" }
+
+[build-dependencies]
+cc = { version = "1.0.1" }
diff --git a/src/szl/build.rs b/src/szl/build.rs
index 971a2917..349572db 100644
--- a/src/szl/build.rs
+++ b/src/szl/build.rs
@@ -1,28 +1,14 @@
-use std::process::Command;
 use std::env;
 use std::fs::File;
 use std::io::Write;
 use std::path::{Path, PathBuf};
 
 fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
     let out = env::var("OUT_DIR").unwrap();
     let out_dir = &PathBuf::from(&out);
 
-    let status = Command::new("clang")
-                              .args(&["-target", "armv7-unknown-linux", "-fno-stack-protector",
-                                      "src/unlzma.c", "-O2", "-c", "-fPIC", "-o",
-                                      &format!("{}/unlzma.o", out)])
-                              .status().unwrap();
-    assert!(status.success());
-    let status = Command::new("llvm-ar")
-                              .args(&["crus", "libunlzma.a", "unlzma.o"])
-                              .current_dir(&Path::new(&out))
-                              .status().unwrap();
-    assert!(status.success());
-    println!("cargo:rustc-link-search=native={}", out);
-    println!("cargo:rustc-link-lib=static=unlzma");
-    println!("cargo:rerun-if-changed=src/unlzma.c");
-
+    compile_unlzma();
     // Put the linker script somewhere the linker can find it
     File::create(out_dir.join("link.x"))
         .unwrap()
@@ -34,3 +20,29 @@ fn main() {
     // instead of when any part of the source code changes.
     println!("cargo:rerun-if-changed=link.x");
 }
+
+pub fn compile_unlzma() {
+    let cfg = &mut cc::Build::new();
+    cfg.compiler("clang");
+    cfg.no_default_flags(true);
+    cfg.warnings(false);
+
+    cfg.flag("-nostdlib");
+    cfg.flag("-ffreestanding");
+    cfg.flag("-fPIC");
+    cfg.flag("-fno-stack-protector");
+    cfg.flag("--target=armv7-unknown-linux");
+    cfg.flag("-O2");
+
+    let sources = vec![
+        "unlzma.c",
+    ];
+
+    let root = Path::new("./");
+    for src in sources {
+        println!("cargo:rerun-if-changed={}", src);
+        cfg.file(root.join("src").join(src));
+    }
+
+    cfg.compile("unlzma");
+}