Update README.md

README.md

@@ -11,8 +11,14 @@ To compile, you need:
 - `nasm` for compiling the bootloader
 - `qemu-system-i386` for emulating (`qemu-system-x86_64` will probably work too, but that is not directly supported)
 
+More information about installing a cross compiler can be found [here](https://wiki.osdev.org/GCC_Cross-Compiler#The_Build).
+
 If you run `make bin`, it will generate `target/boot.bin`, this is a binary file layed out as described in [the docs](docs/bootloader.md). To burn it on a USB drive, simply `dd if=target/boot.bin of=/dev/sdb` and the drive is bootable and contains an SFS filesystem with the files in `filesystem/`.
 
+In case there are errors in the bootloader you can use `make compile_kernel` to only compile the kernel.
+
+To run TABS in the qemu simulator run `make run`.
+
 ## Bootloader
 
 The bootloader is self-written, based on articles on [the OSDev wiki](https://wiki.osdev.org/). It's a single stage, ELF-loading bootloader in the most basic way possible.

kernel/exception.c

@@ -21,65 +21,60 @@ __attribute__((interrupt)) void NAME (interrupt_frame* frame, uint32_t err_code)
     bsod(frame, STR, err_code); \
 }
 
-terminal_state state;
-
-void exception_set_terminal_state(terminal_state* s){
-    terminal_state_copy(s,&state);
-}
-
 void bsod(interrupt_frame* frame, char* err_msg, int32_t err_code) {
 
-    terminal_write_str(&state,"An exception occured: ");
+    terminal_initialize();
-    terminal_write_str(&state,err_msg);
+    terminal_writestring("An exception occured: ");
+    terminal_writestring(err_msg);
     if(err_code != -1) {
-        terminal_write_str(&state," (error code = 0x");
+        terminal_writestring(" (error code = 0x");
-        terminal_write_int(&state,err_code, 16);
+        terminal_writeint(err_code, 16);
-        terminal_write_str(&state,")");
+        terminal_writestring(")");
     }
-    terminal_write_str(&state,"\nHere's what we know:\n");
+    terminal_writestring("\nHere's what we know:\n");
-    terminal_write_str(&state,"eip = 0x");
+    terminal_writestring("eip = 0x");
-    terminal_write_int(&state,frame->eip, 16);
+    terminal_writeint(frame->eip, 16);
-    terminal_write_str(&state,"\ncs = 0x");
+    terminal_writestring("\ncs = 0x");
-    terminal_write_int(&state,frame->cs, 16);
+    terminal_writeint(frame->cs, 16);
-    terminal_write_str(&state,"\neflags = 0b");
+    terminal_writestring("\neflags = 0b");
-    terminal_write_int(&state,frame->eflags, 2);
+    terminal_writeint(frame->eflags, 2);
-    terminal_write_str(&state,"\n(");
+    terminal_writestring("\n(");
 
-    terminal_write_str(&state,(0x0001 & frame->eflags) != 0 ? "NC,": "CY,");
+    terminal_writestring((0x0001 & frame->eflags) != 0 ? "NC,": "CY,");
-    terminal_write_str(&state,(0x0004 & frame->eflags) != 0 ? "PE,": "PO,");
+    terminal_writestring((0x0004 & frame->eflags) != 0 ? "PE,": "PO,");
-    terminal_write_str(&state,(0x0010 & frame->eflags) != 0 ? "AC,": "NA,");
+    terminal_writestring((0x0010 & frame->eflags) != 0 ? "AC,": "NA,");
-    terminal_write_str(&state,(0x0040 & frame->eflags) != 0 ? "ZR,": "NZ,");
+    terminal_writestring((0x0040 & frame->eflags) != 0 ? "ZR,": "NZ,");
-    terminal_write_str(&state,(0x0080 & frame->eflags) != 0 ? "NG,": "PL,");
+    terminal_writestring((0x0080 & frame->eflags) != 0 ? "NG,": "PL,");
-    terminal_write_str(&state,"TF:");
+    terminal_writestring("TF:");
-    terminal_write_int(&state,(0x0100 & frame->eflags) >> 8, 2);
+    terminal_writeint((0x0100 & frame->eflags) >> 8, 2);
-    terminal_write_char(&state,',');
+    terminal_putchar(',');
-    terminal_write_str(&state,(0x0200 & frame->eflags) != 0 ? "EI,": "DI,");
+    terminal_writestring((0x0200 & frame->eflags) != 0 ? "EI,": "DI,");
-    terminal_write_str(&state,(0x0400 & frame->eflags) != 0 ? "DN,": "UP,");
+    terminal_writestring((0x0400 & frame->eflags) != 0 ? "DN,": "UP,");
-    terminal_write_str(&state,(0x0800 & frame->eflags) != 0 ? "OV,": "NV,");
+    terminal_writestring((0x0800 & frame->eflags) != 0 ? "OV,": "NV,");
-    terminal_write_str(&state,"IOPL:");
+    terminal_writestring("IOPL:");
-    terminal_write_int(&state,(0x3000 & frame->eflags) >> 12, 10);
+    terminal_writeint((0x3000 & frame->eflags) >> 12, 10);
-    terminal_write_char(&state,',');
+    terminal_putchar(',');
-    terminal_write_str(&state,"NT:");
+    terminal_writestring("NT:");
-    terminal_write_int(&state,(0x4000 & frame->eflags) >> 14, 2);
+    terminal_writeint((0x4000 & frame->eflags) >> 14, 2);
-    terminal_write_char(&state,',');
+    terminal_putchar(',');
-    terminal_write_str(&state,"RF:");
+    terminal_writestring("RF:");
-    terminal_write_int(&state,(0x0001000 & frame->eflags) >> 16, 2);
+    terminal_writeint((0x0001000 & frame->eflags) >> 16, 2);
-    terminal_write_char(&state,',');
+    terminal_putchar(',');
-    terminal_write_str(&state,"VM:");
+    terminal_writestring("VM:");
-    terminal_write_int(&state,(0x0002000 & frame->eflags) >> 17, 2);
+    terminal_writeint((0x0002000 & frame->eflags) >> 17, 2);
-    terminal_write_char(&state,',');
+    terminal_putchar(',');
-    terminal_write_str(&state,"AC:");
+    terminal_writestring("AC:");
-    terminal_write_int(&state,(0x0004000 & frame->eflags) >> 18, 2);
+    terminal_writeint((0x0004000 & frame->eflags) >> 18, 2);
-    terminal_write_char(&state,',');
+    terminal_putchar(',');
-    terminal_write_str(&state,"VIF:");
+    terminal_writestring("VIF:");
-    terminal_write_int(&state,(0x0008000 & frame->eflags) >> 19, 2);
+    terminal_writeint((0x0008000 & frame->eflags) >> 19, 2);
-    terminal_write_char(&state,',');
+    terminal_putchar(',');
-    terminal_write_str(&state,"VIP:");
+    terminal_writestring("VIP:");
-    terminal_write_int(&state,(0x0010000 & frame->eflags) >> 20, 2);
+    terminal_writeint((0x0010000 & frame->eflags) >> 20, 2);
-    terminal_write_char(&state,',');
+    terminal_putchar(',');
-    terminal_write_str(&state,"ID:");
+    terminal_writestring("ID:");
-    terminal_write_int(&state,(0x0020000 & frame->eflags) >> 21, 2);
+    terminal_writeint((0x0020000 & frame->eflags) >> 21, 2);
-    terminal_write_char(&state,')');
+    terminal_putchar(')');
 
     for(;;) {
         asm("hlt");

kernel/kernel.c

@@ -27,25 +27,20 @@ static inline bool are_interrupts_enabled() {
 
 void kernel_main(void) 
 {
-    terminal_state state;
+	/* Initialize terminal interface */
-    terminal_initialize_state(&state);
+	terminal_initialize();
 
-    terminal_set_color(&state, VGA_COLOR_BLACK, VGA_COLOR_RED);
+	terminal_putchar('H');
-	terminal_write_char(&state, 'H');
+	terminal_putchar('e');
-    terminal_set_color(&state, VGA_COLOR_BLACK, VGA_COLOR_GREEN);
+	terminal_putchar('l');
-	terminal_write_char(&state, 'e');
+	terminal_putchar('l');
-    terminal_set_color(&state, VGA_COLOR_BLACK, VGA_COLOR_BLUE);
+	terminal_putchar('o');
-	terminal_write_char(&state, 'l');
-    terminal_set_color(&state, VGA_COLOR_BLACK, VGA_COLOR_MAGENTA);
-	terminal_write_char(&state, 'l');
-    terminal_set_color(&state, VGA_COLOR_BLACK, VGA_COLOR_WHITE);
-	terminal_write_char(&state, 'o');
  
-    terminal_set_color(&state, VGA_COLOR_GREEN, VGA_COLOR_WHITE);
+    terminal_setcolor(vga_entry_color(VGA_COLOR_GREEN, VGA_COLOR_BLACK));
-    terminal_write_str(&state," kernel");
+    terminal_writestring(" kernel");
-    terminal_set_color(&state, VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
+    terminal_setcolor(vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK));
-    terminal_write_str(&state," World!\n");
+    terminal_writestring(" World!\n");
-	terminal_write_str(&state,"Newlines!\n");
+	terminal_writestring("Newlines!\n");
 
 	char* memory_str = alloc(sizeof(char) * 7);
 	for (int i = 0; i < 6; i++) {
@@ -59,13 +54,11 @@ void kernel_main(void)
 	}
 	management_str[13] = 0;
 
-	/* terminal_write_str(&state,memory_str); */
+	terminal_writestring(memory_str);
-	/* terminal_write_str(&state,management_str); */
+	terminal_writestring(management_str);
 
-	terminal_write_str(&state, (are_interrupts_enabled())? "Interrupts!\n": "No interrupts :(\n");
+	terminal_writestring((are_interrupts_enabled())? "Interrupts!\n": "No interrupts :(\n");
 
-    shell_set_terminal_state(&state);
-    exception_set_terminal_state(&state);
 	interrupt_init();
 
 	for(;;) {

kernel/shell.c

@@ -11,36 +11,31 @@
 
 char buffer[SHELL_CMD_BUFFER_SIZE];
 int buffer_idx = 0;
-terminal_state state;
-
-void shell_set_terminal_state(terminal_state* s){
-    terminal_state_copy(s,&state);
-}
 
 int echo(char* input) {
-    terminal_write_str(&state,input);
+    terminal_writestring(input);
-    terminal_write_char(&state,'\n');
+    terminal_putchar('\n');
     return 0;
 }
 
 int hello(char* unused) {
-    terminal_write_str(&state,"Hello, world!\n");
+    terminal_writestring("Hello, world!\n");
     return 0;
 }
 
 int cls(char* unused) {
-    terminal_clear_state(&state);
+    terminal_initialize();
     return 0;
 }
 
 int get_gdt(char* unused) {
     gdt_desc desc = {2,2};
     sgdt(&desc);
-    terminal_write_str(&state,"limit = ");
+    terminal_writestring("limit = ");
-    terminal_write_int(&state,desc.limit, 10);
+    terminal_writeint(desc.limit, 10);
-    terminal_write_str(&state,"\nbase = 0x");
+    terminal_writestring("\nbase = 0x");
-    terminal_write_int(&state,desc.base, 16);
+    terminal_writeint(desc.base, 16);
-    terminal_write_char(&state,'\n');
+    terminal_putchar('\n');
 
     gdt_entry* entries = (gdt_entry*) desc.base;
     int num_entries = (desc.limit+1) / 8;
@@ -51,73 +46,74 @@ int get_gdt(char* unused) {
         uint8_t flags = (entry.flags_limit_higher >> 4);
         bool is_data = ((entry.access_byte & 0b00001000) >> 3) == 0;
         
-        //terminal_write_str(&state,"\nEntry ");
+        //terminal_writestring("\nEntry ");
-        //terminal_write_int(&state,entry_num, 10);
+        //terminal_writeint(entry_num, 10);
-        terminal_write_str(&state,"base = 0x");
+        terminal_writestring("base = 0x");
-        terminal_write_int(&state,base, 16);
+        terminal_writeint(base, 16);
-        terminal_write_str(&state,"\nlimit = 0x");
+        terminal_writestring("\nlimit = 0x");
-        terminal_write_int(&state,limit, 16);
+        terminal_writeint(limit, 16);
-        terminal_write_str(&state,"\nflags = 0b");
+        terminal_writestring("\nflags = 0b");
-        terminal_write_int(&state,(entry.flags_limit_higher >> 4), 2);
+        terminal_writeint((entry.flags_limit_higher >> 4), 2);
 
         if ((flags & 0b1000) == 0) {
-            terminal_write_str(&state," (byte granularity");
+            terminal_writestring(" (byte granularity");
         } else {
-            terminal_write_str(&state," (page granularity");
+            terminal_writestring(" (page granularity");
         }
 
         if ((flags & 0b0100) == 0) {
-            terminal_write_str(&state,", 16 bit)");
+            terminal_writestring(", 16 bit)");
         } else {
-            terminal_write_str(&state,", 32 bit)");
+            terminal_writestring(", 32 bit)");
         }
 
-        terminal_write_str(&state,"\naccess = 0b");
+        terminal_writestring("\naccess = 0b");
-        terminal_write_int(&state,entry.access_byte, 2);
+        terminal_writeint(entry.access_byte, 2);
-        terminal_write_str(&state," (ring ");
+        terminal_writestring(" (ring ");
-        terminal_write_int(&state,(entry.access_byte & 0b01100000) >> 5, 10);
+        terminal_writeint((entry.access_byte & 0b01100000) >> 5, 10);
         if ((entry.access_byte & 0b00010000) == 0) {
-            terminal_write_str(&state,", System");
+            terminal_writestring(", System");
         }
         if (is_data) {
-            terminal_write_str(&state,", Data");
+            terminal_writestring(", Data");
 
             if((entry.access_byte & 0b00000100) == 0) {
-                terminal_write_str(&state," (growing up, ");
+                terminal_writestring(" (growing up, ");
             } else {
-                terminal_write_str(&state," (growing down, ");
+                terminal_writestring(" (growing down, ");
             }
 
             if((entry.access_byte & 0b00000010) == 0) {
-                terminal_write_str(&state,"r--)");
+                terminal_writestring("r--)");
             } else {
-                terminal_write_str(&state,"rw-)");
+                terminal_writestring("rw-)");
             }
         } else {
-            terminal_write_str(&state,", Code");
+            terminal_writestring(", Code");
 
             if((entry.access_byte & 0b00000100) == 0) {
-                terminal_write_str(&state," (non-conforming, ");
+                terminal_writestring(" (non-conforming, ");
             } else {
-                terminal_write_str(&state," (conforming, ");
+                terminal_writestring(" (conforming, ");
             }
 
             if((entry.access_byte & 0b00000010) == 0) {
-                terminal_write_str(&state,"--x)");
+                terminal_writestring("--x)");
             } else {
-                terminal_write_str(&state,"r-x)");
+                terminal_writestring("r-x)");
             }
         }
 
-        terminal_write_str(&state,")\n");
+        terminal_writestring(")\n");
     }
     return 0;
 }
 
 int ree(char* unused) {
-    terminal_write_char(&state,'R');
+    terminal_initialize();
+    terminal_putchar('R');
     for (int i = 1; i < VGA_WIDTH * VGA_HEIGHT; i++) {
-        terminal_write_char(&state,'e');
+        terminal_putchar('e');
     }
     return 0;
 }
@@ -171,7 +167,7 @@ void shell_step() {
     char curr_char = getchar();
 
     if (curr_char == '\n') {
-        terminal_write_char(&state,curr_char);
+        terminal_putchar(curr_char);
         buffer[buffer_idx] = 0;
         int result = run_command(buffer);
         for (int i = 0; i < SHELL_CMD_BUFFER_SIZE; i++) {
@@ -180,18 +176,18 @@ void shell_step() {
         buffer_idx = 0;
 
         if (result == -1) {
-            terminal_write_str(&state,"No such command\n");
+            terminal_writestring("No such command\n");
         }
     } else if (curr_char == 0x08) {
         if (buffer_idx != 0) {
             buffer_idx--;
             buffer[buffer_idx] = 0;
-            terminal_write_char(&state,curr_char);
+            terminal_putchar(curr_char);
         }
     } else {
         buffer[buffer_idx] = curr_char;
         buffer_idx++;
-        terminal_write_char(&state,curr_char);
+        terminal_putchar(curr_char);
     }
 }
 

kernel/terminal.c

@@ -5,11 +5,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#define VGA_WIDTH 80
+static const size_t VGA_WIDTH = 80;
-#define VGA_HEIGHT 25
+static const size_t VGA_HEIGHT = 25;
-#define MAX_ENTRIES (VGA_HEIGHT*VGA_WIDTH)
-#define TERMINAL_BUFFER_START 0xB8000
-#define BLANK_CHAR ' '
 
 /* Hardware text mode color constants. */
 enum vga_color {
@@ -31,127 +28,83 @@ enum vga_color {
 	VGA_COLOR_WHITE = 15,
 };
 
-typedef struct terminal_entry{
+size_t terminal_row;
-    enum vga_color bg_color;
+size_t terminal_column;
-    enum vga_color fg_color;
+uint8_t terminal_color;
-    char value;
+uint16_t* terminal_buffer;
-} terminal_entry;
 
-typedef struct terminal_state{
+uint8_t vga_entry_color(enum vga_color fg, enum vga_color bg) {
-    terminal_entry entries[MAX_ENTRIES];
+	return fg | bg << 4;
-    int position;
-    enum vga_color bg_color, fg_color;
-} terminal_state;
-
-/* Clear the terminal with only blank spaces */
-void __terminal_clear(terminal_state* state){
-    uint16_t* terminal_buffer = (uint16_t*) TERMINAL_BUFFER_START;
-    uint16_t empty_color = VGA_COLOR_BLACK | VGA_COLOR_GREEN << 4;
-    for(size_t y=0;y<VGA_HEIGHT;++y)
-        for(size_t x=0;x<VGA_WIDTH;++x){
-			size_t index = y * VGA_WIDTH + x;
-            terminal_buffer[index] = (uint16_t) ((unsigned char)BLANK_CHAR) | (uint16_t) empty_color << 8;
-        }
 }
  
-/* Initialise a state, i.e. put every char on blank and the default color everywhere */
+uint16_t vga_entry(unsigned char uc, uint8_t color) {
-void terminal_initialize_state(terminal_state* state){
+	return (uint16_t) uc | (uint16_t) color << 8;
-    state->position=0;
-    state->bg_color = VGA_COLOR_BLACK;
-    state->fg_color = VGA_COLOR_WHITE;
-    for(size_t y=0;y<VGA_HEIGHT;++y)
-        for(size_t x=0;x<VGA_WIDTH;++x){
-			size_t index = y * VGA_WIDTH + x;
-            state->entries[index].value = BLANK_CHAR;
-        }
-    __terminal_clear(state);
 }
  
-/* Copy the state from one to the other */
+size_t strlen(const char* str) {
-void terminal_state_copy(terminal_state* from, terminal_state* to){
-    to->position=from->position;
-    to->bg_color = from->bg_color;
-    to->fg_color = from->fg_color;
-    for(size_t y=0;y<VGA_HEIGHT;++y)
-        for(size_t x=0;x<VGA_WIDTH;++x){
-			size_t index = y * VGA_WIDTH + x;
-            to->entries[index].value = from->entries[index].value;
-        }
-}
-
-/* This function will update the terminal buffer with the given state */
-void terminal_update(terminal_state *state){
-    __terminal_clear(state);
-    uint16_t* terminal_buffer = (uint16_t*) TERMINAL_BUFFER_START;
-    for(size_t y=0;y<VGA_HEIGHT;++y)
-        for(size_t x=0;x<VGA_WIDTH;++x){
-			size_t index = y * VGA_WIDTH + x;
-            terminal_entry entry = state->entries[index];
-            uint8_t color = entry.fg_color | entry.bg_color << 4;
-            terminal_buffer[index] = (uint16_t) ((unsigned char)entry.value) | (uint16_t) color << 8;
-        }
-}
-
-/* Update the background color */
-void __terminal_set_bg_color(terminal_state* state, enum vga_color color){
-    state->bg_color = color;
-}
-
-/* Update the foreground color */
-void __terminal_set_fg_color(terminal_state* state, enum vga_color color){
-    state->fg_color = color;
-}
-
-/* Update the color */
-void terminal_set_color(terminal_state* state, enum vga_color bg_color, enum vga_color fg_color){
-    __terminal_set_bg_color(state, bg_color);
-    __terminal_set_fg_color(state, fg_color);
-}
-
-/* Write a char to the state */
-void __terminal_put_char(terminal_state *state, char c){
-    size_t pos = state->position;
-    terminal_entry entry;
-    /* If there is a new line, keep going until the end of the line (with blank space in black) */
-    if(c == '\n'){
-        entry.bg_color = VGA_COLOR_BLACK;
-        entry.fg_color = VGA_COLOR_BLACK;
-        entry.value = BLANK_CHAR;
-        while(pos % VGA_WIDTH){
-            state->entries[pos] = entry;
-            ++pos;
-        }
-        state->position = (pos % MAX_ENTRIES);
-    }
-    else{
-        entry.bg_color = state->bg_color;
-        entry.fg_color = state->fg_color;
-        entry.value = c;
-        state->entries[pos] = entry;
-        state->position = ((pos+1) % MAX_ENTRIES);
-    }
-}
-
-/* Write a char to the state and run an update */
-void terminal_write_char(terminal_state *state, const char c){
-    __terminal_put_char(state, c);
-    terminal_update(state);
-}
-
-/* Write a string to the state and run an update */
-void terminal_write_str(terminal_state *state, const char* str){
 	size_t len = 0;
-    while (str[len]) {
+	while (str[len])
-        __terminal_put_char(state, str[len]);
+		len++;
-        ++len;
+	return len;
-    }
-    terminal_update(state);
 }
 
-/* Clear the terminal en reset the state to the initial state */
+void terminal_initialize(void) {
-void terminal_clear_state(terminal_state* state){
+	terminal_row = 0;
-    __terminal_clear(state);
+	terminal_column = 0;
-    terminal_initialize_state(state);
+	terminal_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
+	terminal_buffer = (uint16_t*) 0xB8000;
+	for (size_t y = 0; y < VGA_HEIGHT; y++) {
+		for (size_t x = 0; x < VGA_WIDTH; x++) {
+			const size_t index = y * VGA_WIDTH + x;
+			terminal_buffer[index] = vga_entry(' ', terminal_color);
+		}
+	}
+}
+ 
+void terminal_setcolor(uint8_t color) {
+	terminal_color = color;
+}
+ 
+void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) {
+	const size_t index = y * VGA_WIDTH + x;
+	terminal_buffer[index] = vga_entry(c, color);
+}
+ 
+void terminal_putchar(char c) {
+	if (c == '\n') {
+		terminal_column = 0;
+		terminal_row++;
+		return;
+	}
+	if (c == 0x08) {
+		terminal_putentryat(' ', terminal_color, terminal_column, terminal_row);
+		if (terminal_column == 0) {
+			if(terminal_row != 0) {
+				terminal_row--;
+				terminal_column = VGA_WIDTH - 1;
+			}
+		} else {
+			terminal_column--;
+		}
+		terminal_putentryat(' ', terminal_color, terminal_column, terminal_row);
+		return;
+	}
+
+	terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
+	if (++terminal_column == VGA_WIDTH) {
+		terminal_column = 0;
+		if (++terminal_row == VGA_HEIGHT)
+			terminal_row = 0;
+	}
+}
+ 
+void terminal_write(const char* data, size_t size) {
+	for (size_t i = 0; i < size; i++)
+		terminal_putchar(data[i]);
+}
+ 
+void terminal_writestring(const char* data) {
+	terminal_write(data, strlen(data));
 }
 
 char* itoa(unsigned int value, char* result, int base) {
@@ -176,10 +129,10 @@ char* itoa(unsigned int value, char* result, int base) {
 	return result;
 }
 
-void terminal_write_int(terminal_state* state,int number, int base) {
+void terminal_writeint(int number, int base) {
 	char* result = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";
 	itoa(number, result, base);
-	terminal_write_str(state, result);
+	terminal_writestring(result);
 }
 
 #endif //TERMINAL_C