Execute an 'init' program (elf) loaded as a grub module

.gitignore

@@ -1,4 +1,5 @@
 /build/
+/init/init
 *.o
 *.a
 *.bin

Makefile

@@ -67,9 +67,10 @@ iso: ## build the image of the OS (.iso)
 iso: $(ISO)
 .PHONY: iso
 
-$(ISO): $(KERNEL)
+$(ISO): $(KERNEL) init
 	mkdir -p $(GRUB_DIR)
 	cp -R grub/* $(GRUB_DIR)
+	cp init/init $(KERNEL_DIR)
 	grub-mkrescue -o $@ $(ISO_DIR)
 
 run: ## run the OS
@@ -100,6 +101,12 @@ gdb: $(ISO)
 	qemu-system-x86_64 -s -S -cdrom $< -serial file:/tmp/serial.log
 .PHONY: gdb
 
+# TODO: there must be a better way to compile different modules from a
+# top-level makefile.
+init: $(LIBC)
+	cd init && make clean && make
+.PHONY: init
+
 help:
 	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
 .PHONY: help

grub/grub.cfg

@@ -3,5 +3,6 @@ set default=0
 
 menuentry "willOS" {
     multiboot2 /boot/kernel.bin
+    module2 /boot/init
     boot
 }

init/Makefile

@@ -0,0 +1,26 @@
+CC   ?= gcc
+LD   ?= ld
+AR   ?= ar
+NASM ?= nasm
+
+ifeq ($(shell uname -s),Darwin)
+	CC = x86_64-pc-elf-gcc
+	LD = x86_64-pc-elf-ld
+	AR = x86_64-pc-elf-ar
+endif
+
+TARGET    = init
+ROOT_DIR  = ..
+BUILD_DIR = .
+CFLAGS    = -Wl,-emain -Wall -pedantic -std=c11 -O2 -ffreestanding -nostdlib -I $(ROOT_DIR)/src/include
+LIBS      = $(ROOT_DIR)/build/libc-willOS.a
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
+$(TARGET): $(TARGET).o
+	$(CC) -o $@ $^ $(CFLAGS) $(LIBS)
+
+clean:
+	rm -rf $(TARGET) *.o
+.PHONY: clean

init/init.c

@@ -0,0 +1,7 @@
+#include <sys/syscall.h>
+
+int main() {
+    test("I'm the init program");
+
+    return 0;
+}

src/core/syscall.c

@@ -32,7 +32,9 @@ void syscall_handler(registers_t* registers) {
 }
 
 void syscall_test(registers_t* registers) {
-    printf("    (syscall_test) hello, %s!\n", registers->rbx);
+    // TODO: remove offset (0x100000) when we have a separate memory area for a
+    // process. See the `elf.c` file for more information.
+    printf("    (syscall_test) hello, %s!\n", (registers->rbx + 0x100000));
 }
 
 void syscall_print_registers(registers_t* registers) {

src/kernel/kmain.c

@@ -1,4 +1,5 @@
 #include "kmain.h"
+#include <core/elf.h>
 #include <core/debug.h>
 #include <core/isr.h>
 #include <core/syscall.h>
@@ -93,6 +94,22 @@ void kmain(uint64_t addr) {
     keyboard_init();
     print_ok();
 
+    multiboot_tag_module_t* module = find_multiboot_tag(mbi, MULTIBOOT_TAG_TYPE_MODULE);
+
+    print_step("loading grub module (elf)");
+    elf_header_t* elf = elf_load((uint64_t*)module->mod_start);
+
+    if (elf) {
+        DEBUG("loaded elf entry=%p", elf->entry);
+        print_ok();
+
+        printf("\n");
+
+        typedef int callable(void);
+        callable* c = (callable*)(elf->entry);
+        int res = c();
+    }
+
     // kshell
     printf("\n");
     kshell_print_prompt();