feat(kernel): linker and source code

src/kernel.c

@@ -0,0 +1,28 @@
+typedef unsigned char u8;
+typedef unsigned int u32;
+typedef u32 size_t;
+
+extern char __bss[], __bss_end[], __stack_top[];
+
+void *memset(void *buf, char c, size_t n) {
+	u8 *p = (u8 *)buf;
+	while (n--) {
+		*p++ = c;
+	}
+
+	return buf;
+}
+
+void kernel_main(void) {
+	memset(__bss, 0, __bss_end - __bss);
+
+	for (;;)
+		;
+}
+
+__attribute__((section(".text.boot"))) __attribute__((naked)) void boot(void) {
+	__asm__ __volatile__("mv sp, %[stack_top]\n"
+						 "j kernel_main\n"
+						 :
+						 : [stack_top] "r"(__stack_top));
+}