Add a syscall infrastructure (our baby program can print to the console now!)

apps/app.asm

@@ -1,4 +1,17 @@
 section .text
 global _start
 _start:
+    mov rax, 1
+    mov rdi, message
     int 42h
+    mov rax, 1
+    mov rdi, message2
+    int 42h
+    mov rax, 0
+    int 42h
+
+section .rodata
+message:
+    db "Hello!", 0xa, 0
+message2:
+    db "I am an app", 0xa, 0

kernel/CMakeLists.txt

@@ -15,6 +15,9 @@ set(SOURCES
     src/thread/Spinlock.cpp
     src/thread/Thread.cpp
     src/thread/Scheduler.cpp
+    src/sys/Syscall.cpp
+    src/sys/exit.cpp
+    src/sys/console_print.cpp
     src/InitRD.cpp
     src/ELF.cpp
 )
@@ -82,4 +85,4 @@ target_include_directories(moon PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/gen)
 
 target_link_options(moon PRIVATE LINKER:-T ${CMAKE_CURRENT_LIST_DIR}/moon.ld -nostdlib -nodefaultlibs)
 
-install(FILES "${CMAKE_CURRENT_BINARY_DIR}/moon" DESTINATION ${LUNA_ROOT}/initrd/boot)
+install(FILES "${CMAKE_CURRENT_BINARY_DIR}/moon" DESTINATION ${LUNA_ROOT}/initrd/boot)

kernel/src/arch/x86_64/CPU.asm

@@ -188,4 +188,4 @@ ISR_ERROR 21 ; control-protection exception (#CP)
 ; ISR 22-31 reserved
 IRQ 32, 0 ; timer interrupt
 IRQ 33, 0 ; keyboard interrupt
-ISR 66 ; user exit
+ISR 66 ; system call

kernel/src/arch/x86_64/CPU.cpp

@@ -4,6 +4,7 @@
 #include "arch/x86_64/CPU.h"
 #include "arch/x86_64/IO.h"
 #include "memory/MemoryManager.h"
+#include "sys/Syscall.h"
 #include "thread/Scheduler.h"
 #include <cpuid.h>
 #include <luna/CString.h>
@@ -107,11 +108,10 @@ extern "C" void arch_interrupt_entry(Registers* regs)
         scancode_queue.try_push(scancode);
         pic_eoi(regs);
     }
-    else if (regs->isr == 66) // Exit!!
+    else if (regs->isr == 66) // System call
     {
-        kdbgln("exiting from user task!!");
-        Scheduler::current()->state = ThreadState::Dying;
-        kernel_yield();
+        SyscallArgs args = { regs->rdi, regs->rsi, regs->rdx, regs->r10, regs->r8, regs->r9 };
+        regs->rax = (u64)invoke_syscall(regs, args, regs->rax);
     }
     else
     {

kernel/src/sys/Syscall.cpp

@@ -0,0 +1,18 @@
+#include "sys/Syscall.h"
+#include <luna/SystemError.h>
+
+syscall_func_t syscalls[] = {
+#undef __enumerate
+#define __enumerate(name) sys_##name,
+    enumerate_syscalls(__enumerate)
+#undef __enumerate
+};
+
+i64 invoke_syscall(Registers* regs, SyscallArgs args, u64 syscall)
+{
+    if (syscall >= Syscalls::__count) { return -ENOSYS; }
+
+    auto rc = syscalls[syscall](regs, args);
+    if (rc.has_error()) return -rc.error();
+    return (i64)rc.value();
+}

kernel/src/sys/Syscall.h

@@ -0,0 +1,16 @@
+#pragma once
+#include "arch/CPU.h"
+#include <luna/Result.h>
+#include <luna/Syscall.h>
+
+typedef u64 SyscallArgs[6];
+
+typedef Result<u64> (*syscall_func_t)(Registers*, SyscallArgs);
+
+// Invoked by the architecture-dependent system call entry point.
+i64 invoke_syscall(Registers*, SyscallArgs, u64 syscall);
+
+#undef __enumerate
+#define __enumerate(name) extern Result<u64> sys_##name(Registers*, SyscallArgs);
+enumerate_syscalls(__enumerate)
+#undef __enumerate

kernel/src/sys/console_print.cpp

@@ -0,0 +1,12 @@
+#include "memory/MemoryManager.h"
+#include "sys/Syscall.h"
+#include "video/TextConsole.h"
+
+Result<u64> sys_console_print(Registers*, SyscallArgs args)
+{
+    if (!MemoryManager::validate_userspace_string(args[0])) return err(EFAULT);
+
+    TextConsole::print((char*)args[0]);
+
+    return { 0 };
+}

kernel/src/sys/exit.cpp

@@ -0,0 +1,7 @@
+#include "sys/Syscall.h"
+#include "thread/Scheduler.h"
+
+Result<u64> sys_exit(Registers*, SyscallArgs)
+{
+    kernel_exit();
+}

luna/include/luna/Syscall.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#define enumerate_syscalls(_e) _e(exit) _e(console_print)
+
+enum Syscalls
+{
+#undef __enumerate
+#define __enumerate(name) SYS_##name,
+    enumerate_syscalls(__enumerate)
+#undef __enumerate
+        __count
+};