Added libc functions

Makefile

@@ -3,7 +3,7 @@ CFLAGS = -nostdlib -O2 -g3 -Wall -Wextra -fno-stack-protector -ffreestanding
 LD_SCRIPT = kernel.ld
 LDFLAGS = -T$(LD_SCRIPT) -Wl,-Map=kernel.map
 
-SRC = kernel.c
+SRC = kernel.c common.c
 OUT = kernel.elf
 
 .PHONY: all clean run

common.c

@@ -0,0 +1,122 @@
+#include "common.h"
+
+void putchar(char c);
+
+size_t align_up(size_t value, size_t align)
+{
+    /* To align means to compute the smallest value which is greater than a
+     * given number and that is an exact multiple of another specified
+     * number */
+    size_t remainder = value % align;
+    if (remainder == 0)
+        return value;
+
+    return value + (align - remainder);
+}
+
+size_t is_aligned(size_t value, size_t align)
+{
+    return value % align == 0;
+}
+
+void *memcpy(void *dst, const void *src, size_t n)
+{
+    uint8_t *d = (uint8_t*)dst;
+    const uint8_t *s = (uint8_t*)src;
+    while (n--) {
+        *d++ = *s++;
+    }
+    return dst;
+}
+
+void *memset(void *buf, char c, size_t n)
+{
+    uint8_t *p = (uint8_t*)buf;
+    while (n--) {
+        *p++ = c;
+    }
+    return buf;
+}
+
+char *strcpy(char *dst, const char *src)
+{
+    char *d = dst;
+    while (*src != '\0') {
+        *d++ = *src++;
+    }
+    *d = '\0';
+    return dst;
+}
+
+int strcmp(const char *s1, const char *s2)
+{
+    while (*s1 && *s2 && *s1 == *s2) {
+        s1++;
+        s2++;
+    }
+    return *((unsigned char *)s1) - *((unsigned char *)s2);
+}
+
+void printf(const char *fmt, ...)
+{
+    va_list args;
+    va_start(args, fmt);
+    while (*fmt != '\0') {
+        if (*fmt != '%') {
+            putchar(*fmt);
+            fmt++;
+        } else {
+            fmt++; // consume %
+            switch (*fmt) {
+            case '\0':
+                putchar('%');
+                goto end;
+            case '%':
+                putchar('%');
+                break;
+            case 's':
+                const char *s = va_arg(args, const char*);
+                while (*s != '\0') {
+                    putchar(*s);
+                    s++;
+                }
+                break;
+            case 'd':
+                int num = va_arg(args, int);
+                unsigned int magnitude = num;
+                unsigned int power = 1;
+                if (num < 0) {
+                    putchar('-');
+                    magnitude = -magnitude;
+                }
+
+                while ((magnitude / power) > 9) {
+                    power *= 10;
+                }
+
+                while (power > 0) {
+                    putchar('0' + (magnitude / power));
+                    magnitude %= power;
+                    power /= 10;
+                }
+                break;
+            case 'x':
+                unsigned int hex = va_arg(args, unsigned int);
+                putchar('0');
+                putchar('x');
+                for (int i = 7; i >= 0; i--) {
+                    unsigned int nibble = (hex >> (4 * i)) & 0xf;
+                    putchar("0123456789abcdef"[nibble]);
+                }
+                break;
+            }
+
+            fmt++; // consume modifier
+        }
+    }
+
+end:
+    va_end(args);
+
+    return;
+}

common.h

@@ -0,0 +1,36 @@
+#ifndef COMMON_H_
+#define COMMON_H_
+
+#define true 1
+#define false 0
+
+#define NULL ((void*)0)
+
+#define va_list __builtin_va_list
+#define va_start __builtin_va_start
+#define va_end __builtin_va_end
+#define va_arg __builtin_va_arg
+
+#define offsetof(type, member) ((size_t)&(((type*)0)->member))
+
+typedef int bool;
+typedef unsigned char uint8_t;
+typedef unsigned short uint16_t ;
+typedef unsigned int uint32_t;
+
+typedef uint32_t size_t;
+typedef uint32_t paddr_t;
+typedef uint32_t vaddr_t ;
+
+void printf(const char *fmt, ...);
+
+size_t align_up(size_t value, size_t align);
+size_t is_aligned(size_t value, size_t align);
+
+void *memcpy(void *dst, const void *src, size_t n);
+void *memset(void *buf, char c, size_t n);
+
+char *strcpy(char *dst, const char *src);
+int strcmp(const char *s1, const char *s2);
+
+#endif // COMMON_H_

kernel.c

@@ -1,4 +1,5 @@
 #include "kernel.h"
+#include "common.h"
 
 extern uint8_t __bss[], __bss_end[], __stack_top[];
 
@@ -32,10 +33,14 @@ void putchar(char c)
 
 void kernel_main(void)
 {
-    const char *s = "\n\nHello World!\n";
-    for (int i = 0; s[i] != '\0'; i++) {
-        putchar(s[i]);
-    }
+    const char *s = "Hello World!";
+    printf("\nString = '%s'\n", s);
+    printf("\nPositive Integer = %d\n", 42);
+    printf("\nNegative Integer = %d\n", -42);
+    printf("\nHexadecimal = %x\n", 0xdeadbeef);
+
+    printf("offsetof(sbiret, error) = %x\n", offsetof(sbiret, error));
+    printf("offsetof(sbiret, value) = %x\n", offsetof(sbiret, value));
 
     while(1) {
         // wfi -> wait for interrupt

kernel.h

@@ -1,10 +1,6 @@
 #ifndef KERNEL_H_
 #define KERNEL_H_
 
-typedef unsigned char uint8_t;
-typedef unsigned int uint32_t;
-typedef uint32_t size_t;
-
 typedef struct {
     long error;
     long value;