Add an apps/ folder and build-system to build userspace apps which can now be loaded from the initrd

apps/Makefile

@@ -10,7 +10,7 @@ ASMC := nasm
 ASMFLAGS := -felf64
 
 LD := x86_64-elf-ld
-APP_LDFLAGS := -T$(APPS_DIR)/apps.ld -nostdlib
+APP_LDFLAGS := -T$(APPS_DIR)/apps.ld -nostdlib -z max-page-size=0x1000
 
 $(APPS_OBJ)/%.o: $(APPS_DIR)/%.asm
 	@mkdir -p $(@D)

apps/apps.ld

@@ -1,9 +1,10 @@
 ENTRY(_start)
 OUTPUT_FORMAT(elf64-x86-64)
 
+. = 0x2f00000000;
+
 SECTIONS
 {
-    . = 0x10000;
     .text : ALIGN(16) {
         KEEP(*(.text.boot)) *(.text .text.*)   /* code */
         *(.rodata .rodata.*)                   /* data */

apps/init.asm

@@ -1,5 +1,24 @@
 section .text
 global _start
 _start:
+    mov rax, 1
+    int 42h
+    mov rdi, HelloLabel
+    mov rsi, 22
+    mov rax, 3
+    int 42h
+    mov rdi, 400
+    mov rax, 2
+    int 42h
+    mov rdi, ExitLabel
+    mov rsi, 31
+    mov rax, 3
+    int 42h
     mov rax, 0
-    int 42h
+    int 42h
+
+section .rodata
+HelloLabel:
+    db "Hello from /bin/init!", 0xA
+ExitLabel:
+    db "Well, bye. (/bin/init exiting)", 0xA

kernel/src/interrupts/InterruptEntry.asm

@@ -40,6 +40,7 @@ extern common_handler
 section .text
 global asm_common
 asm_common:
+    cli
     cld
     push rax
     push rbx

kernel/src/main.cpp

@@ -28,6 +28,7 @@
 #include "std/stdio.h"
 #include "std/stdlib.h"
 #include "std/string.h"
+#include "sys/elf/ELFLoader.h"
 #include "thread/PIT.h"
 #include "thread/Scheduler.h"
 
@@ -125,10 +126,13 @@ extern "C" void _start()
         }
     });
 
-    uint64_t userspace_phys = kernelVMM.getPhysical((uint64_t)_userspace);
-    if (userspace_phys == UINT64_MAX) panic("_userspace is not mapped");
-    kernelVMM.map(0x7000, userspace_phys, MAP_USER);
-    Scheduler::add_user_task((void*)(0x7000 + ((uint64_t)_userspace % 4096)));
+    void* elf_start_address = ELFLoader::load_elf_from_initrd("bin/init");
+    if (!elf_start_address) kerrorln("failed to load /bin/init from initrd");
+    else
+    {
+        kinfoln("loaded /bin/init at %lx", (uint64_t)elf_start_address);
+        Scheduler::add_user_task(elf_start_address);
+    }
 
     kinfoln("Prepared scheduler tasks");