better exception handling + bad kprintf

Makefile

@@ -8,7 +8,7 @@ CC=i686-elf-gcc
 bootstrap.o: bootstrap.s
 	i686-elf-as bootstrap.s -o bootstrap.o
 
-kernel.bin: bootstrap.o vga.o std/std.o cpu/idt.o cpu/pic.o kernel.o 
+kernel.bin: bootstrap.o vga.o std/std.o std/kstd.o cpu/idt.o cpu/pic.o cpu/exception.o kernel.o
 	$(CC) -T linker.ld -o $@ -ffreestanding -O2 -nostdlib -lgcc $^
 
 iso: kernel.bin
@@ -18,7 +18,7 @@ iso: kernel.bin
 	grub-mkrescue -o generated-iso.iso isodir
 
 run: iso
-	qemu-system-i386 -cdrom generated-iso.iso
+	qemu-system-i386 -d int -M smm=off -cdrom generated-iso.iso
 
 clean:
 	rm -rf *.o kernel.bin *.iso isodir/

cpu/exception.c

@@ -0,0 +1,130 @@
+#include "cpu/idt.h"
+#include "std/std.h"
+#include "std/kstd.h"
+
+void generic_exception_handler(struct interrupt_descriptor_32 *frame, uint8_t irq) {
+    kprintf("\n\n");
+    kprintf("---- PANIC -------------\n");
+    kprintf("Kernel panic due to exception\n");
+    kprintf("IRQ %d\n", (int)irq);
+    kprintf("------------------------\n");
+    kabort();
+}
+
+__attribute__((interrupt))
+static void isr0(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 0);
+}
+
+__attribute__((interrupt))
+static void isr1(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 1);
+}
+
+__attribute__((interrupt))
+static void isr2(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 2);
+}
+
+__attribute__((interrupt))
+static void isr3(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 3);
+}
+
+__attribute__((interrupt))
+static void isr4(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 4);
+}
+
+__attribute__((interrupt))
+static void isr5(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 5);
+}
+
+__attribute__((interrupt))
+static void isr6(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 6);
+}
+
+__attribute__((interrupt))
+static void isr7(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 7);
+}
+
+__attribute__((interrupt))
+static void isr8(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 8);
+}
+
+__attribute__((interrupt))
+static void isr9(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 9);
+}
+
+__attribute__((interrupt))
+static void isr10(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 10);
+}
+
+__attribute__((interrupt))
+static void isr11(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 11);
+}
+
+__attribute__((interrupt))
+static void isr12(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 12);
+}
+
+__attribute__((interrupt))
+static void isr13(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 13);
+}
+
+__attribute__((interrupt))
+static void isr14(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 14);
+}
+
+__attribute__((interrupt))
+static void isr15(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 15);
+}
+
+__attribute__((interrupt))
+static void isr16(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 16);
+}
+
+__attribute__((interrupt))
+static void isr17(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 17);
+}
+
+__attribute__((interrupt))
+static void isr18(struct interrupt_descriptor_32 *frame) {
+    generic_exception_handler(frame, 17);
+}
+
+
+void exception_handlers_init() {
+    idt_register_handler(0, (size_t)isr0);
+    idt_register_handler(1, (size_t)isr1);
+    idt_register_handler(2, (size_t)isr2);
+    idt_register_handler(3, (size_t)isr3);
+    idt_register_handler(4, (size_t)isr4);
+    idt_register_handler(5, (size_t)isr5);
+    idt_register_handler(6, (size_t)isr6);
+    idt_register_handler(7, (size_t)isr7);
+    idt_register_handler(8, (size_t)isr8);
+    idt_register_handler(9, (size_t)isr9);
+    idt_register_handler(10, (size_t)isr10);
+    idt_register_handler(11, (size_t)isr11);
+    idt_register_handler(12, (size_t)isr12);
+    idt_register_handler(13, (size_t)isr13);
+    idt_register_handler(14, (size_t)isr14);
+    idt_register_handler(15, (size_t)isr15);
+    idt_register_handler(16, (size_t)isr16);
+    idt_register_handler(17, (size_t)isr17);
+    idt_register_handler(18, (size_t)isr18);
+}

cpu/exception.h

@@ -0,0 +1,6 @@
+#ifndef _EXCEPTION_H
+#define _EXCEPTION_H
+
+void exception_handlers_init();
+
+#endif

cpu/idt.h

@@ -8,13 +8,13 @@
 #define INTERRUPT_GATE              0x8e
 
 // https://wiki.osdev.org/Interrupt_Descriptor_Table
-struct __attribute__((__packed__)) interrupt_descriptor_32 {
+struct interrupt_descriptor_32 {
     uint16_t offset_1;        // offset bits 0..15
     uint16_t selector;        // a code segment selector in GDT or LDT
     uint8_t  zero;            // unused, set to 0
     uint8_t  type_attributes; // gate type, dpl, and p fields
     uint16_t offset_2;        // offset bits 16..31
-};
+} __attribute__((__packed__)); 
 
 void idt_init();
 void idt_register_handler(uint8_t interrupt, size_t address);

kernel.c

@@ -4,6 +4,7 @@
 #include "vga.h"
 #include "cpu/pic.h"
 #include "cpu/idt.h"
+#include "std/kstd.h"
 
 #if defined(__linux__)
 #error "You are not using a cross-compiler, you will most certainly run into trouble"
@@ -13,32 +14,23 @@
 #error "This OS needs to be compiled with a ix86-elf compiler"
 #endif
 
-struct interrupt_frame
-{
-    size_t ip;
-    size_t cs;
-    size_t flags;
-    size_t sp;
-    size_t ss;
-} __attribute__((packed));
-
-__attribute__((interrupt))
-static void isr0(struct interrupt_frame *frame) {
-    terminal_writestring("division by zero");
-    pic_send_eoi(0);
-}
-
 void kmain(void) {
     terminal_initialize();
 
-    terminal_writestring("start");
+    kprintf("kmain(): info: kernel init started\n");
 
+    kprintf("[    ] Remapping PIC");
     pic_remap(0x20, 0x28);
-    idt_register_handler(0, (size_t)isr0);
+    kprintf("\r[ OK ]\n");
+
+    kprintf("[    ] Installing exception handlers");
+    exception_handlers_init();
+    kprintf("\r[ OK ]\n");
+
+    kprintf("[    ] Initializing IDT");
     idt_init();
+    kprintf("\r[ OK ]\n");
 
-    volatile int a = 0/0;
+    terminal_writestring("Initialization finished.\n");
-
-    terminal_writestring("Hello, kernel World!\n");
 }
 

std/kstd.c

@@ -0,0 +1,127 @@
+#include <stdarg.h>
+#include <limits.h>
+#include "std/kstd.h"
+#include "std/std.h"
+#include "vga.h"
+
+int putchar(int ic) {
+	char c = (char) ic;
+	terminal_write(&c, sizeof(c));
+	return ic;
+}
+
+static bool print(const char* data, size_t length) {
+	const unsigned char* bytes = (const unsigned char*) data;
+	for (size_t i = 0; i < length; i++) {
+        if (putchar(bytes[i]) == (-1)) { // EOF??
+            return false;
+        }
+    }
+	return true;
+}
+
+// https://wiki.osdev.org/Meaty_Skeleton
+int kprintf(const char* restrict format, ...) {
+    va_list parameters;
+    va_start(parameters, format);
+ 
+    int written = 0;
+ 
+    while (*format != '\0') {
+        size_t maxrem = INT_MAX - written;
+ 
+        if (format[0] != '%' || format[1] == '%') {
+            if (format[0] == '%')
+                format++;
+            size_t amount = 1;
+            while (format[amount] && format[amount] != '%')
+                amount++;
+            if (maxrem < amount) {
+                // TODO: Set errno to EOVERFLOW.
+                return -1;
+            }
+            if (!print(format, amount))
+                return -1;
+            format += amount;
+            written += amount;
+            continue;
+        }
+ 
+        const char* format_begun_at = format++;
+ 
+        if (*format == 'c') {
+            format++;
+            char c = (char) va_arg(parameters, int /* char promotes to int */);
+            if (!maxrem) {
+                // TODO: Set errno to EOVERFLOW.
+                return -1;
+            }
+            if (!print(&c, sizeof(c)))
+                return -1;
+            written++;
+        } else if (*format == 's') {
+            format++;
+            const char* str = va_arg(parameters, const char*);
+            size_t len = strlen(str);
+            if (maxrem < len) {
+                // TODO: Set errno to EOVERFLOW.
+                return -1;
+            }
+            if (!print(str, len))
+                return -1;
+            written += len;
+        } else if (*format == 'd') {
+            format++;
+            int val = va_arg(parameters, int);
+            int base = 10;
+            char *str;
+
+            // note: flawed implementation
+            // based on: https://www.strudel.org.uk/itoa/
+            if (val == 0) {
+                str = "0\0";
+            } else {
+                static char buf[32] = {0};
+                int i = 30;
+                for(; val && i ; --i, val /= base) {
+                    buf[i] = "0123456789abcdef"[val % base];
+                }
+                str = &buf[i+1];
+            }
+
+            size_t len = strlen(str);
+            if (maxrem < len) {
+                // TODO: Set errno to EOVERFLOW.
+                return -1;
+            }
+            print(str, len);
+            written += len;
+        } else {
+            format = format_begun_at;
+            size_t len = strlen(format);
+            if (maxrem < len) {
+                // TODO: Set errno to EOVERFLOW.
+                return -1;
+            }
+            if (!print(format, len))
+                return -1;
+            written += len;
+            format += len;
+        }
+    }
+ 
+    va_end(parameters);
+    return written;
+}
+
+void kputs(const char* data) {
+    kprintf("%s\n", data);
+}
+
+void kabort() {
+    kprintf("kabort(): halting kernel...\n");
+    asm volatile("cli");
+    asm volatile("hlt");
+    while (1) {}
+    __builtin_unreachable();
+}

std/kstd.h

@@ -0,0 +1,11 @@
+#ifndef _KSTD_H
+#define _KSTD_H
+
+#include <stdbool.h>
+
+int putchar(int ic);
+int kprintf(const char* restrict format, ...);
+void kputs(const char* data);
+void kabort();
+
+#endif

std/std.c

@@ -40,4 +40,3 @@ void* memcpy(void *destv, void *srcv, size_t size) {
 
     return destv;
 }
-

vga.c

@@ -29,11 +29,21 @@ void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) {
 }
  
 void terminal_putchar(char c) {
-    terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
+    switch (c) {
-    if (++terminal_column == VGA_WIDTH) {
+        case '\r':
-        terminal_column = 0;
+            terminal_column = 0;
-        if (++terminal_row == VGA_HEIGHT)
+            break;
-            terminal_row = 0;
+        case '\n':
+            terminal_column = 0;
+            terminal_row++;
+            break;
+        default:
+            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;
+            }
     }
 }