From a6598886f0f46eab06c624cabadf82403c4c22cc Mon Sep 17 00:00:00 2001
From: Alexander Myltsev <a.myltsev@gmail.com>
Date: Wed, 14 Dec 2022 16:50:10 +0300
Subject: [PATCH] Add two syscalls.

---
 Makefile      |  4 ++--
 cpu/idt.c     | 22 ++++++++++++++++++++++
 cpu/isr.h     |  1 -
 cpu/vectors.S |  4 ++--
 proc.c        |  6 ++++++
 proc.h        |  1 +
 syscall.h     |  9 +++++++++
 user/crt.c    |  9 ++++++++-
 user/greet.c  |  7 +++++++
 9 files changed, 57 insertions(+), 6 deletions(-)
 create mode 100644 syscall.h
 create mode 100644 user/greet.c

diff --git a/Makefile b/Makefile
index 9615153..2e8fc22 100644
--- a/Makefile
+++ b/Makefile
@@ -47,8 +47,8 @@ debug-nox: image.bin
 		-ex "break _start" \
 		-ex "continue"
 
-fs.img: kernel.bin tools/mkfs user/false
-	tools/mkfs $@ $< user/false
+fs.img: kernel.bin tools/mkfs user/false user/greet
+	tools/mkfs $@ $< user/false user/greet
 
 LDFLAGS=-m elf_i386
 
diff --git a/cpu/idt.c b/cpu/idt.c
index 60cf250..4b4137c 100644
--- a/cpu/idt.c
+++ b/cpu/idt.c
@@ -1,5 +1,7 @@
 #include "isr.h"
 #include "gdt.h"
+#include "../syscall.h"
+#include "../proc.h"
 #include "../drivers/port.h"
 #include "../console.h"
 
@@ -83,6 +85,26 @@ void register_interrupt_handler(uint8_t i, isr_t handler) {
 }
 
 void trap(registers_t *r) {
+    if (r->int_no == T_SYSCALL) {
+        switch (r->eax) {
+            case SYS_exit:
+                if (r->ebx == 0) {
+                    printk("* success\n");
+                } else {
+                    printk("* failure\n");
+                }
+                killproc();
+            case SYS_greet:
+                printk("Hello world!\n");
+                r->eax = 0;
+                break;
+            default:
+                printk("Unknown syscall\n");
+                r->eax = -1;
+        }
+        return;
+    }
+
     if (r->int_no < 32) {
         const char* msg = "Reserved";
         if (r->int_no < ARRLEN(exception_messages)) {
diff --git a/cpu/isr.h b/cpu/isr.h
index e7d52fd..de12f30 100644
--- a/cpu/isr.h
+++ b/cpu/isr.h
@@ -18,7 +18,6 @@ enum {
     IRQ13,
     IRQ14,
     IRQ15,
-    T_SYSCALL = 0x84,
 };
 
 /* Struct which aggregates many registers.
diff --git a/cpu/vectors.S b/cpu/vectors.S
index 21ddded..b1131fb 100644
--- a/cpu/vectors.S
+++ b/cpu/vectors.S
@@ -8,8 +8,8 @@ alltraps:
     pushl %gs
     pushal
 
-    //mov $10, %ax
-    //mov %ax, %ds
+    mov $0x10, %ax
+    mov %ax, %ds
     
     # Call trap(tf), where tf=%esp
     pushl %esp
diff --git a/proc.c b/proc.c
index 6b19510..48d9800 100644
--- a/proc.c
+++ b/proc.c
@@ -67,3 +67,9 @@ void run_elf(const char* name) {
 
     // process has finished
 }
+
+_Noreturn void killproc() {
+    void* task_stack;
+    swtch(&task_stack, vm->kernel_thread);
+    __builtin_unreachable();
+}
diff --git a/proc.h b/proc.h
index 86a4322..54ede88 100644
--- a/proc.h
+++ b/proc.h
@@ -1,3 +1,4 @@
 #pragma once
 
 void run_elf(const char* name);
+_Noreturn void killproc();
diff --git a/syscall.h b/syscall.h
new file mode 100644
index 0000000..4c9ba03
--- /dev/null
+++ b/syscall.h
@@ -0,0 +1,9 @@
+#pragma once
+
+enum {
+	T_SYSCALL = 0x84,
+	SYS_exit = 0,
+	SYS_greet = 1,
+};
+
+int syscall(int call, int arg);
diff --git a/user/crt.c b/user/crt.c
index 17320ea..5032810 100644
--- a/user/crt.c
+++ b/user/crt.c
@@ -1,8 +1,15 @@
+#include "../syscall.h"
+
 int main();
 
+int syscall(int call, int arg) {
+    asm("int $0x84": "+a"(call) : "b"(arg));
+    return call;
+}
+
 _Noreturn
 void _exit(int exit_status) {
-    asm("int $0x84": : "a"(0), "b"(exit_status));
+    syscall(SYS_exit, exit_status);
     __builtin_unreachable();
 }
 
diff --git a/user/greet.c b/user/greet.c
new file mode 100644
index 0000000..28b539b
--- /dev/null
+++ b/user/greet.c
@@ -0,0 +1,7 @@
+#include "../syscall.h"
+
+int main(void) {
+    syscall(SYS_greet, 0);
+    syscall(SYS_greet, 0);
+    return 0;
+}