Fix some review problems, add mispel arch to CI

Signed-off-by: Harry Chen <i@harrychen.xyz>

.travis.yml

@@ -28,6 +28,7 @@ env:
     - ARCH="riscv32"
     - ARCH="x86_64"
     - ARCH="aarch64"
+    - ARCH="mipsel" OPTS="board=malta"
 
 matrix:
     allow_failures:
@@ -90,6 +91,15 @@ install:
     export PATH=$PATH:$PWD/riscv64-linux-musl-cross/bin;
     fi;
     fi
+  - if [ $ARCH = mipsel ]; then
+    if [ $TRAVIS_OS_NAME = linux ]; then
+    sudo apt update;
+    sudo apt install linux-headers-$(uname -r);
+    wget https://musl.cc/mipsel-linux-musln32-cross.tgz;
+    tar -xvf mipsel-linux-musln32-cross.tgz;
+    export PATH=$PATH:$PWD/mipsel-linux-musln32-cross/bin;
+    fi;
+    fi
 
 
 before_script:

kernel/Makefile

@@ -136,7 +136,7 @@ qemu_opts += \
 else ifeq ($(arch), mipsel)
 ifeq ($(board), malta)
 qemu_opts += \
-	-machine $(board) \
+	-machine $(board) -device VGA \
 	-serial null -serial null -serial mon:stdio \
 	-kernel $(kernel_img)
 endif

kernel/src/arch/mipsel/atomic.patch

@@ -1,72 +0,0 @@
---- atomic_backup.rs	2018-10-06 19:59:14.000000000 +0800
-+++ atomic.rs	2018-10-26 14:34:31.000000000 +0800
-@@ -125,6 +125,9 @@
- #[cfg(target_has_atomic = "8")]
- #[stable(feature = "rust1", since = "1.0.0")]
- pub struct AtomicBool {
-+    #[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
-+    v: UnsafeCell<u32>,
-+    #[cfg(not(any(target_arch = "riscv32", target_arch = "riscv64")))]
-     v: UnsafeCell<u8>,
- }
- 
-@@ -265,6 +268,59 @@
- pub const ATOMIC_BOOL_INIT: AtomicBool = AtomicBool::new(false);
- 
- #[cfg(target_has_atomic = "8")]
-+#[cfg(any(target_arch = "riscv32", target_arch = "riscv64"))]
-+impl AtomicBool {
-+    ///
-+    #[inline]
-+    #[stable(feature = "rust1", since = "1.0.0")]
-+    pub const fn new(v: bool) -> AtomicBool {
-+        AtomicBool { v: UnsafeCell::new(v as u32) }
-+    }
-+
-+    ///
-+    #[inline]
-+    #[stable(feature = "rust1", since = "1.0.0")]
-+    pub fn load(&self, order: Ordering) -> bool {
-+        unsafe { atomic_load(self.v.get(), order) != 0 }
-+    }
-+
-+    ///
-+    #[inline]
-+    #[stable(feature = "rust1", since = "1.0.0")]
-+    pub fn store(&self, val: bool, order: Ordering) {
-+        unsafe { atomic_store(self.v.get(), val as u32, order); }
-+    }
-+
-+    ///
-+    #[inline]
-+    #[stable(feature = "rust1", since = "1.0.0")]
-+    pub fn compare_and_swap(&self, current: bool, new: bool, order: Ordering) -> bool {
-+        match self.compare_exchange(current, new, order, strongest_failure_ordering(order)) {
-+            Ok(x) => x,
-+            Err(x) => x,
-+        }
-+    }
-+
-+    ///
-+    #[inline]
-+    #[stable(feature = "extended_compare_and_swap", since = "1.10.0")]
-+    pub fn compare_exchange(&self,
-+                            current: bool,
-+                            new: bool,
-+                            success: Ordering,
-+                            failure: Ordering)
-+                            -> Result<bool, bool> {
-+        match unsafe {
-+            atomic_compare_exchange(self.v.get(), current as u32, new as u32, success, failure)
-+        } {
-+            Ok(x) => Ok(x != 0),
-+            Err(x) => Err(x != 0),
-+        }
-+    }
-+}
-+
-+#[cfg(target_has_atomic = "8")]
-+#[cfg(not(any(target_arch = "riscv32", target_arch = "riscv64")))]
- impl AtomicBool {
-     /// Creates a new `AtomicBool`.
-     ///