Add terminal scrolling

This closes #2.

5 files changed, 81 insertions, 23 deletions

diff --git a/Makefile b/Makefile
index cb64d5e..f248f46 100644
--- a/Makefile
+++ b/Makefile
@@ -13,9 +13,9 @@ target/kernel.o: target/boot.o target/i686-lisibleos/release/libkernel.a
 
 target/i686-lisibleos/release/libkernel.a:
 	mkdir -p target
-	xargo build -p kernel --target i686-lisibleos --release
+	RUST_TARGET_PATH=$(shell pwd) xargo build -p kernel --target i686-lisibleos --release
 
 clean:
-	xargo clean --target i686-lisibleos
+	RUST_TARGET_PATH=$(shell pwd) xargo clean --target i686-lisibleos
 	rm target/kernel.o target/boot.o target/i686-lisibleos/debug/libkernel.a
 	rm target/kernel.o target/boot.o target/i686-lisibleos/release/libkernel.a
diff --git a/kernel/Cargo.toml b/kernel/Cargo.toml
index 1ca49e6..e5b9b67 100644
--- a/kernel/Cargo.toml
+++ b/kernel/Cargo.toml
@@ -10,3 +10,5 @@ edition = "2018"
 [lib]
 crate-type = ["staticlib"]
 
+[dependencies]
+compiler_builtins = { version = "0.1.50", features = ["mem"] }
diff --git a/kernel/src/io.rs b/kernel/src/io.rs
index b6b4cc7..def8665 100644
--- a/kernel/src/io.rs
+++ b/kernel/src/io.rs
@@ -1,7 +1,5 @@
-pub fn out8(address: u16, value: u8) {
-    unsafe {
-        asm!(
-            "out dx, al", in("dx") address, in("al") value
-        )
-    }
-}
\ No newline at end of file
+pub unsafe fn out8(address: u16, value: u8) {
+    asm!(
+        "out dx, al", in("dx") address, in("al") value
+    )
+}
diff --git a/kernel/src/lib.rs b/kernel/src/lib.rs
index b6bc55f..edb5704 100644
--- a/kernel/src/lib.rs
+++ b/kernel/src/lib.rs
@@ -12,8 +12,32 @@ mod terminal;
 pub extern "C" fn kmain() -> ! {
     let mut terminal = Terminal::new();
     terminal.clear();
-    terminal.put_string(b"LisibleOS\n");
-    terminal.put_string(b"> ");
+    terminal.put_string(b"1 LisibleOS\n");
+    terminal.put_string(b"2 > \n");
+    terminal.put_string(b"3\n");
+    terminal.put_string(b"4\n");
+    terminal.put_string(b"5\n");
+    terminal.put_string(b"6\n");
+    terminal.put_string(b"7\n");
+    terminal.put_string(b"8\n");
+    terminal.put_string(b"9\n");
+    terminal.put_string(b"10\n");
+    terminal.put_string(b"11\n");
+    terminal.put_string(b"12\n");
+    terminal.put_string(b"13\n");
+    terminal.put_string(b"14\n");
+    terminal.put_string(b"15\n");
+    terminal.put_string(b"16\n");
+    terminal.put_string(b"17\n");
+    terminal.put_string(b"18\n");
+    terminal.put_string(b"19\n");
+    terminal.put_string(b"20\n");
+    terminal.put_string(b"21\n");
+    terminal.put_string(b"22\n");
+    terminal.put_string(b"23\n");
+    terminal.put_string(b"24\n");
+    terminal.put_string(b"25\n");
+    terminal.put_string(b"26");
     loop {}
 }
 
diff --git a/kernel/src/terminal.rs b/kernel/src/terminal.rs
index 2a5cf1a..9e3eec1 100644
--- a/kernel/src/terminal.rs
+++ b/kernel/src/terminal.rs
@@ -1,4 +1,5 @@
 use crate::io;
+use compiler_builtins::mem::memcpy;
 
 const VGA_BUFFER_POINTER: *mut u8 = 0xb8000 as *mut u8;
 const VGA_BUFFER_SIZE: u16 = 4000;
@@ -28,15 +29,17 @@ impl Terminal {
 
     pub fn put_char(&mut self, c: u8) {
         if c == b'\n' {
-            self.current_row += 1;
-            if self.current_row == ROW_COUNT {
-                self.current_row = 0;
+            if self.current_row < ROW_COUNT - 1 {
+                self.current_row += 1;
+            } else {
+                self.scroll_y(-1);
             }
 
             self.current_col = 0;
             return;
         }
 
+        /// Safety: This is safe because VGA_BUFFER_POINTER points toward the VGA character buffer
         unsafe {
             *VGA_BUFFER_POINTER.offset(
                 ((self.current_col as isize + self.current_row as isize * COL_COUNT as isize)
@@ -48,32 +51,63 @@ impl Terminal {
 
     fn compute_current_position(&mut self) {
         if self.current_col == COL_COUNT - 1 {
-            if self.current_row == ROW_COUNT - 1 {
-                self.current_col = 0;
-                self.current_row = 0;
-            } else {
+            if self.current_row != ROW_COUNT - 1 {
                 self.current_row = (self.current_row + 1) % ROW_COUNT;
+            } else {
+                self.scroll_y(-1);
             }
+            self.current_col = 0;
+        } else {
+            self.current_col = (self.current_col + 1) % COL_COUNT;
         }
-        self.current_col = (self.current_col + 1) % COL_COUNT;
+    }
+
+    fn scroll_y(&mut self, y: i8) {
+        // Safety:
+        // The starting pointer is in bound because it's the VGA character buffer pointer
+        // The end pointer isn't past the VGA character buffer pointer
+        // The offset doesn't overflow isize
+        // The offset doesn't rely on wrapping around the address space
+        let src = unsafe { VGA_BUFFER_POINTER.offset(COL_COUNT as isize * VALUE_SIZE as isize) };
+        let dest = VGA_BUFFER_POINTER;
+        let size = (VGA_BUFFER_SIZE as usize - COL_COUNT as usize) * VALUE_SIZE as usize;
+
+        // Safety:
+        // dest and src are valid pointer to the same object being the VGA character buffer
+        // This copy will not go  past the VGA character buffer
+        unsafe { memcpy(dest, src, size) };
+
+        self.clear_line(ROW_COUNT - 1);
     }
 
     pub fn put_char_at(&mut self, c: u8, row: u8, col: u8) {
         self.current_row = row;
         self.current_col = col;
-        self.put_char(c);
+        unsafe {
+            *VGA_BUFFER_POINTER.offset(
+                ((self.current_col as isize + self.current_row as isize * COL_COUNT as isize)
+                    * VALUE_SIZE as isize),
+            ) = c;
+        }
     }
 
     pub fn clear(&mut self) {
         for row in 0..ROW_COUNT {
-            for col in 0..COL_COUNT {
-                self.put_char_at(b' ', row, col);
-            }
+            self.clear_line(row)
         }
         self.current_col = 0;
         self.current_row = 0;
     }
 
+    fn clear_line(&mut self, row: u8) {
+        for col in 0..COL_COUNT {
+            self.put_char_at(b' ', row, col);
+        }
+
+        self.current_row = row;
+        self.current_col = 0;
+    }
+
     pub fn set_cursor_position(&mut self, row: u8, col: u8) {
         let cursor_position: u16 = (row * COL_COUNT + col) as u16;
         let address_register = 0x3D4;