Implemented project structure

kernel.c

@@ -0,0 +1,56 @@
+#include "kernel.h"
+
+extern uint8_t __bss[], __bss_end[], __stack_top[];
+
+sbiret sbi_call(long arg0, long arg1, long arg2, long arg3, long arg4,
+                long arg5, long fid, long eid)
+{
+    register long a0 __asm__("a0") = arg0;
+    register long a1 __asm__("a1") = arg1;
+    register long a2 __asm__("a2") = arg2;
+    register long a3 __asm__("a3") = arg3;
+    register long a4 __asm__("a4") = arg4;
+    register long a5 __asm__("a5") = arg5;
+    register long a6 __asm__("a6") = fid;
+    register long a7 __asm__("a7") = eid;
+
+    __asm__ __volatile__(
+        "ecall"
+        : "=r"(a0), "=r"(a1)
+        : "r"(a0), "r"(a1), "r"(a2), "r"(a3), "r"(a4), "r"(a5), "r"(a6), "r"(a7)
+        : "memory"
+    );
+
+    return (sbiret) { .error = a0, .value = a1 };
+}
+
+void putchar(char c)
+{
+    // 1 => sbi_console_putchar()
+    sbi_call(c, 0, 0, 0, 0, 0, 0, 1);
+}
+
+void kernel_main(void)
+{
+    const char *s = "\n\nHello World!\n";
+    for (int i = 0; s[i] != '\0'; i++) {
+        putchar(s[i]);
+    }
+
+    while(1) {
+        // wfi -> wait for interrupt
+        __asm__ __volatile__("wfi");
+    }
+}
+
+__attribute__((section(".text.boot")))
+__attribute__((naked))
+void boot(void)
+{
+    __asm__ __volatile__ (
+        "mv sp, %[stack_top]\n"         // Initialize the kernel stack pointer
+        "j kernel_main\n"               // Unconditional jump to kernel_main
+        :                               // No output
+        : [stack_top] "r" (__stack_top) // Pass the stack top address
+    );
+}