tock-responder: Implement more libc stubs

tock-responder/src/libc_stubs.rs

@@ -18,16 +18,36 @@ fn libspdm_get_random_number_64(rand_data: *mut u64) -> bool {
     if let Err(why) = Rng::get_bytes_sync(&mut rng_buf, 8) {
         panic!("rng error: {:?}", why);
     }
-    assert!(
-        rng_buf.iter().any(|&x| x != 0),
-        "Unlikely that all elements are zero"
-    );
+    let rng = u64::from_be_bytes(rng_buf);
+    assert_ne!(rng, 0);
     unsafe {
-        *rand_data = u64::from_be_bytes(rng_buf);
+        *rand_data = rng;
     }
     true
 }
 
+#[no_mangle]
+/// Return a random integer between [0 and i32::MAX].
+pub extern "C" fn rand() -> i32 {
+    if let Err(why) = Rng::exists() {
+        panic!("rng error: {:?}", why);
+    }
+    // Request 4 bytes of RNG.
+    let mut rng_buf: [u8; 4] = [0; 4];
+    if let Err(why) = Rng::get_bytes_sync(&mut rng_buf, 4) {
+        panic!("rng error: {:?}", why);
+    }
+
+    let mut rng = i32::from_be_bytes(rng_buf);
+    // The valid output range is [0, i32::MAX], so if the signed bit is
+    // set from HW RNG, invert it.
+    if rng < 0 {
+        rng = rng.wrapping_neg();
+    }
+    assert_ne!(rng, 0);
+    rng
+}
+
 // Based on https://github.com/llvm/llvm-project/blob/main/compiler-rt/lib/builtins/bswapsi2.c
 #[no_mangle]
 pub extern "C" fn __bswapsi2(u: u32) -> u32 {
@@ -103,8 +123,69 @@ pub extern "C" fn time() {
 }
 
 #[no_mangle]
-pub extern "C" fn strncmp() {
-    todo!("libc/stub: strncmp(): not yet implemented");
+/// Compare no more than N characters of S1 and S2,
+/// returning less than, equal to or greater than zero
+/// if S1 is lexicographically less than, equal to or
+/// greater than S2.
+/// Based on: https://github.com/zerovm/glibc/blob/3f07350498160f552350dc39f6fe6d237c7c3b03/string/strncmp.c#L28C4-L29C20
+pub extern "C" fn strncmp(s1: *const c_char, s2: *const c_char, n: usize) -> i32 {
+    let mut s1 = s1;
+    let mut s2 = s2;
+    let mut n = n;
+
+    let mut c1: u8 = b'\0';
+    let mut c2: u8 = b'\0';
+
+    if n >= 4 {
+        let mut n4 = n >> 2;
+        while n4 > 0 {
+            c1 = unsafe { *s1 as u8 };
+            s1 = unsafe { s1.offset(1) };
+            c2 = unsafe { *s2 as u8 };
+            s2 = unsafe { s2.offset(1) };
+            if c1 == b'\0' || c1 != c2 {
+                return (c1 as i32) - (c2 as i32);
+            }
+            c1 = unsafe { *s1 as u8 };
+            s1 = unsafe { s1.offset(1) };
+            c2 = unsafe { *s2 as u8 };
+            s2 = unsafe { s2.offset(1) };
+            if c1 == b'\0' || c1 != c2 {
+                return (c1 as i32) - (c2 as i32);
+            }
+            c1 = unsafe { *s1 as u8 };
+            s1 = unsafe { s1.offset(1) };
+            c2 = unsafe { *s2 as u8 };
+            s2 = unsafe { s2.offset(1) };
+            if c1 == b'\0' || c1 != c2 {
+                return (c1 as i32) - (c2 as i32);
+            }
+            c1 = unsafe { *s1 as u8 };
+            s1 = unsafe { s1.offset(1) };
+            c2 = unsafe { *s2 as u8 };
+            s2 = unsafe { s2.offset(1) };
+            if c1 == b'\0' || c1 != c2 {
+                return (c1 as i32) - (c2 as i32);
+            }
+
+            n4 -= 1;
+        }
+        n &= 3;
+    }
+
+    while n > 0 {
+        c1 = unsafe { *s1 as u8 };
+        s1 = unsafe { s1.offset(1) };
+        c2 = unsafe { *s2 as u8 };
+        s2 = unsafe { s2.offset(1) };
+        if c1 == b'\0' || c1 != c2 {
+            return (c1 as i32) - (c2 as i32);
+        }
+
+        n -= 1;
+    }
+
+    (c1 as i32) - (c2 as i32)
 }
 
 #[no_mangle]
@@ -121,8 +202,3 @@ pub extern "C" fn strchr() {
 pub extern "C" fn strcmp() {
     todo!("libc/stub: strcmp(): not yet implemented");
 }
-
-#[no_mangle]
-pub extern "C" fn rand() {
-    todo!("libc/stub: rand(): not yet implemented");
-}