src/kernel/irq.c

@@ -25,6 +25,8 @@ extern void irq13();
 extern void irq14();
 extern void irq15();
 
+extern void syscall_common_stub();
+
 void *irq_routines[16] =
 {
 	0, 0, 0, 0, 0, 0, 0, 0,
@@ -76,6 +78,8 @@ void irq_install()
 	idt_set_gate(46, (unsigned)irq14, 0x08, 0x8E);
 	idt_set_gate(47, (unsigned)irq15, 0x08, 0x8E);
 	printf("[kernel] installed irq 0-15\n");
+
+	idt_set_gate(0x80, (unsigned long)syscall_common_stub, 0x08, 0x8E);
 }
 
 void irq_handler(struct regs *r)

src/kernel/loader.s

@@ -210,6 +210,37 @@ irq_common_stub:
 	add esp, 8
 	iret
 
+; we'll be placing the syscall_common_stub here.
+; push everything, then call syscall_handler (be sure to define it extern)
+; then pop back everything and iret
+extern syscall_handler
+
+global syscall_common_stub
+syscall_common_stub:
+	pusha
+	push ds
+	push es
+	push fs
+	push gs
+	
+	mov eax, ds
+	push eax	; save ds
+	mov ax, 0x10	; kernel segment
+	mov ds, ax
+	mov es, ax
+	
+	call syscall_handler
+
+	pop eax
+	mov ds, eax	; restore ds
+
+	pop gs
+	pop fs
+	pop es
+	pop ds
+	popa
+	iret
+
 section .bss
 align 4 
 

src/kernel/syscall.c

@@ -1,20 +0,0 @@
-#include <stdarg.h>
-#include "../libc/stdio.h"
-#include "syscall.h"
-
-syscall_t syscalls[] = {
-	(syscall_t)printf,
-};
-
-int syscall_handler(int syscall_num, ...)
-{
-	if ((unsigned)syscall_num < sizeof(syscalls)/sizeof(syscall_t))
-	{
-		va_list args;
-		va_start(args, syscall_num);
-		syscalls[syscall_num](va_arg(args, const char*));
-		va_end(args);
-		return 0;
-	}
-	return -1;
-}

src/kernel/syscall.h

@@ -1,8 +0,0 @@
-#ifndef SYSCALL_H
-#define SYSCALL_H
-
-#define SYSCALL_PRINTF 0
-
-typedef void (*syscall_t)();
-
-#endif

src/kernel/syscalls.c

@@ -0,0 +1,33 @@
+// System calls
+// Author: xamidev
+// Licensed under the Unlicense. See the repo below.
+// https://github.com/xamidev/blankos
+
+#include "../libc/stdio.h"
+
+void handle_syscall(int syscall_number, void* arg)
+{
+	switch(syscall_number)
+	{
+		case 1:
+			puts("Here's the syscall 1\n");
+			break;
+		default:
+			printf("[error] Invalid syscall number '%d'!\n", syscall_number);
+			break;
+	}
+}
+
+void syscall_handler()
+{
+	int syscall_number;
+	void* arg;
+	// mov eax, syscall_number
+	// mov ebx, arg
+	asm volatile("mov %%eax, %0" : "=r"(syscall_number));
+	asm volatile("mov %%ebx, %0" : "=r"(arg));
+
+	printf("[syscall] syscall_number=%d, arg=%p\n", syscall_number, arg);
+
+	handle_syscall(syscall_number, arg);
+}

src/kernel/system.h

@@ -39,5 +39,7 @@ extern volatile unsigned long global_ticks;
 
 extern unsigned int g_multiboot_info_address;
 
+void syscall_handler();
+
 #endif
 

src/programs/hello.c

@@ -1,9 +1,10 @@
-void user_printf(const char* format) {
-    asm volatile ("int $0x80" : : "a"(1), "b"(format));
+void user_syscall(int syscall_no) {
+	asm volatile ("mov %0, %%eax" : : "r"(syscall_no));
+	asm volatile ("int $0x80"); 
 }
 
 void main()
 {
-	user_printf("Hello, world, from a PROGRAM!\n");
+	user_syscall(1);
 	return;
 }