syscall: cleanup interface, registration and argument parsing

Signed-off-by: Mahavir Jain <[email protected]>

boot/syscall.s

@@ -15,3 +15,9 @@ execve:
 	mov eax, 2
 	int 64
 	ret
+
+[GLOBAL read]
+sleep:
+	mov eax, 3
+	int 64
+	ret

drivers/vga.c

@@ -2,6 +2,7 @@
 #include <string.h>
 #include <helper.h>
 #include <vm.h>
+#include <syscall.h>
 
 extern void memsetw(void *src, uint16_t value, size_t size);
 
@@ -65,7 +66,7 @@ static void cls()
 	move_cursor(_x, _y);
 }
 
-void vga_write_char(char c)
+void sys_write_char(char c)
 {
 	uint16_t *loc = fb + (_y * 80 + _x);
 	uint8_t attr = COLOR_ATTR;
@@ -99,14 +100,21 @@ void vga_write_char(char c)
 	move_cursor(_x, _y);
 }
 
-void vga_write_buf(char *buf, int len)
+int sys_write()
 {
+	const char *buf;
+	int len;
+
+	argstr(1, (char **) &buf);
+	argint(2, &len);
+
 	if (!buf || !len)
-		return;
+		return 0;
 
-	while (len--)
-		vga_write_char(*buf++);
-	return;
+	int i;
+	for (i = 0; i < len; i++)
+		sys_write_char(buf[i]);
+	return len;
 }
 
 void init_vga()

include/drivers/vga.h

@@ -2,8 +2,8 @@
 #define __VGA_H__
 
 void init_vga();
-void vga_write_char(char ch);
-void vga_write_buf(char *buf, int len);
+void sys_write_char(char ch);
+int sys_write(char *buf, int len);
 int printk(const char *fmt, ...);
 
 #endif /* __VGA_H__ */

include/kernel/syscall.h

@@ -0,0 +1,8 @@
+#ifndef __SYSCALL_H__
+#define __SYSCALL_H__
+
+void syscall_handler(registers_t *r);
+int argint(int n, int *p);
+int argstr(int n, char **p);
+
+#endif /* __SYSCALL_H__ */

include/kernel/task.h

@@ -46,7 +46,7 @@ void init_scheduler();
 void tiny_schedule(void);
 int create_init_task(void);
 int sys_fork(void);
-int sys_exec(const char *fname);
+int sys_exec(void);
 void swtch(struct context **old, struct context *new);
 void yield();
 void sched();

kernel/isr.c

@@ -2,6 +2,7 @@
 #include <vga.h>
 #include <helper.h>
 #include <task.h>
+#include <syscall.h>
 
 static void *irq_handlers[256];
 
@@ -73,26 +74,6 @@ void irq_uninstall_handler(int irq)
 	irq_handlers[irq] = 0;
 }
 
-static void syscall_handler(registers_t *r)
-{
-	/* write system call */
-	if (r->eax == 0) {
-		/* First argument is fd, ignore for now */
-		/* buffer to print on VGA */
-		char *buf = (char *) (*(int *)(r->useresp + 8));
-		/* length of buffer */
-		int len = *(int *) (r->useresp + 12);
-		vga_write_buf(buf, len);
-	/* fork system call */
-	} else if (r->eax == 1) {
-		/* FIXME: do we need to set current task `irqf` to `r` here? */
-		r->eax = sys_fork();
-	} else if (r->eax == 2) {
-		char *fname = (char *) (*(int *)(r->useresp + 4));
-		r->eax = sys_exec(fname);
-	}
-}
-
 // This gets called from our ASM interrupt handler stub.
 void irq_handler(registers_t *r)
 {

kernel/keyboard.c

@@ -78,7 +78,7 @@ void keyboard_handler(registers_t *r)
 		 *  to the above layout to correspond to 'shift' being
 		 *  held. If shift is held using the larger lookup table,
 		 *  you would add 128 to the scancode when you look for it */
-		vga_write_char(kbdus[scancode]);
+		sys_write_char(kbdus[scancode]);
 	}
 }
 

kernel/syscall.c

@@ -0,0 +1,42 @@
+#include <isr.h>
+#include <vga.h>
+#include <helper.h>
+#include <task.h>
+
+static registers_t *irqf;
+
+static void *sys_handlers[] = {
+	sys_write,
+	sys_fork,
+	sys_exec,
+	//sys_read,
+};
+
+int argint(int n, int *p)
+{
+	/* FIXME: Need some error checking here */
+	*p = *(int *)(irqf->useresp + 4 + 4*n);
+	return 0;
+}
+
+int argstr(int n, char **p)
+{
+	/* FIXME: Need some error checking here */
+	*p = *(char **)(irqf->useresp + 4 + 4*n);
+	return 0;
+}
+
+void syscall_handler(registers_t *r)
+{
+	int num = r->eax;
+	int (*func) (void);
+
+	irqf = r;
+	if (num < ARR_SIZE(sys_handlers) && sys_handlers[r->eax]) {
+		func = sys_handlers[r->eax];
+		r->eax = func();
+	} else {
+		printk("Unsupported syscall %d\n", num);
+	}
+	irqf = NULL;
+}

kernel/task.c

@@ -8,6 +8,7 @@
 #include <gdt.h>
 #include <cpio_parser.h>
 #include <elf.h>
+#include <syscall.h>
 
 /* Task list */
 static list_head_t *task_list;
@@ -197,10 +198,14 @@ int sys_fork()
 	return pid;
 }
 
-int sys_exec(const char *fname)
+int sys_exec()
 {
+	char *fname;
 	int ret;
 	unsigned long size;
+
+	argstr(0, &fname);
+
 	void *fstart = cpio_get_file(_binary_ramfs_cpio_start,
 					fname, &size);
 	if (!fstart) {

stdlib/printk.c

@@ -7,7 +7,7 @@ extern int dec_to_str(const int num, char buf[]);
 static void write_str(const char *buf)
 {
 	while (*buf)
-		vga_write_char(*buf++);
+		sys_write_char(*buf++);
 }
 
 int printk(const char *fmt, ...)
@@ -22,7 +22,7 @@ int printk(const char *fmt, ...)
 	va_start(ap, fmt);
 	for (p = fmt; *p; p++) {
 		if (*p != '%') {
-			vga_write_char(*p);
+			sys_write_char(*p);
 			continue;
 		}
 		switch (*++p) {
@@ -53,7 +53,7 @@ int printk(const char *fmt, ...)
 			/* need a cast here since va_arg only
 			   takes fully promoted types */
 			c = (char) va_arg(ap, int);
-			vga_write_char(c);
+			sys_write_char(c);
 			break;
 		}
 	}