Call a c function.

src/kernel/Makefile

@@ -6,7 +6,7 @@ SRC := $(wildcard **/*.[cS])
 OBJ := $(patsubst %, %.o, $(basename $(SRC)))
 
 CFLAGS ?= -Wall -Wextra -pedantic
-CFLAGS += -ffreestanding
+CFLAGS += -ffreestanding -mcmodel=large
 CFLAGS += -ggdb -O0
 ASFLAGS += -ggdb
 CPPFLAGS += -I include

src/kernel/boot/boot.S

@@ -65,5 +65,6 @@ _start:
   mov rax, 0
   movabs [BootP4], rax
 
-  //; Loop infinitely
-  jmp $
+.extern kmain
+  movabs rax, offset kmain
+  jmp rax

src/kernel/boot/kmain.c

@@ -0,0 +1,26 @@
+#include <memory.h>
+
+void clear_screen()
+{
+  unsigned char *vidmem = (void *)(0xB8000 + KERNEL_OFFSET);
+  for(int i=0; i < 80*24*2; i++)
+    *vidmem++ = 0;
+}
+
+void print_string(char *str)
+{
+  unsigned char *vidmem = (void *)(0xB8000 + KERNEL_OFFSET);
+  while(*str)
+  {
+    *vidmem++ = *str++;
+    *vidmem++ = 0x7;
+  }
+}
+
+void kmain()
+{
+  clear_screen();
+  print_string("Hello from c, world!");
+  for(;;);
+}
+