more userlaand stuff

kernel/idt.c

@@ -4,6 +4,7 @@
 #define IDT_MAX_DESCRIPTORS 256
 
 #define ATTR_KERN_32 0x8E // active(1), ring 0 (00), interrupt gate(0), 32 bit (1110)
+#define ATTR_USER_32 0xEE // active, ring 3, 32bit
 
 #define SEGMENT_KERN 0x08
 
@@ -31,11 +32,11 @@ void* isr_stub_table[256] = {
 idt_entry idt[IDT_MAX_DESCRIPTORS];
 idt_ptr idtr;
 
-void set_idtr(uint8_t vector, void* isr, uint8_t attributes) {
+void set_idtr(uint8_t vector, void* isr, uint16_t sel, uint8_t attributes) {
     idt_entry* desc = &idt[vector];
 
     desc->isr_low    = (uint32_t)isr & 0xFFFF;
-    desc->kernel_cs  = SEGMENT_KERN;
+    desc->selector  = SEGMENT_KERN;
     desc->reserved   = 0;
     desc->attributes = attributes;
     desc->isr_high   = ((uint32_t)isr >> 16) & 0xFFFF;
@@ -47,11 +48,14 @@ void init_idt() {
 
     for (int i = 0; i < IDT_MAX_DESCRIPTORS; i++) {
         if (isr_stub_table[i] != 0) {
-            set_idtr(i, isr_stub_table[i], ATTR_KERN_32);
+            set_idtr(i, isr_stub_table[i], SEGMENT_KERN, ATTR_KERN_32);
         } else {
-            set_idtr(i, 0, 0);
+            set_idtr(i, 0, SEGMENT_KERN, 0);
         }
     }
 
+    extern void syscall_handler();
+    set_idtr(0x80, syscall_handler, SEGMENT_KERN, ATTR_USER_32);
+
     load_idt();
 }

kernel/idt.h

@@ -4,11 +4,11 @@
 #include <stdint.h>
 
 typedef struct __attribute__((packed)){
-    uint16_t isr_low;   // The lower 16 bits of the ISR's address
-    uint16_t kernel_cs; // The GDT segment selector the CPU will load into CS
-    uint8_t  reserved;  // Set to 0
-    uint8_t  attributes;// Type and attributes flags
-    uint16_t isr_high;  // The higher 16 bits of the ISR's address
+    uint16_t isr_low; 
+    uint16_t selector; 
+    uint8_t  reserved;  
+    uint8_t  attributes;
+    uint16_t isr_high; 
 } idt_entry;
 
 typedef struct __attribute__((packed)){

kernel/kmain.c

@@ -88,7 +88,7 @@ void load_origin_program(multiboot_info* mbi) {
   kprintf("program loaded into memory @ [virt] 0x%x\n", elf->e_entry);
 
   extern void liftoff(uint32_t entry, uint32_t stack_top);
-  kprintf("launching origin process");
+  kprintf("launching origin process\n");
   uint32_t stack_top =  0xBFFFF000 + 4095;
   liftoff(elf->e_entry, stack_top);
 }

kernel/memory/mm.c

@@ -25,7 +25,7 @@ static uint8_t memory_bitmap[BITMAP_SIZE];
 
 static void mark_free(uint32_t addr) {
     uint32_t page_index = addr / PAGE_SIZE;
-    uint32_t byte_index = page_index / 8;
+    uint32_t byte_index = page_index / 8;   
     uint32_t bit_index = page_index % 8;
     memory_bitmap[byte_index] &= ~(1 << bit_index);
 }

kernel/syscall.c

@@ -0,0 +1,27 @@
+#include <stdint.h>
+
+#include "lib/print.h"
+
+typedef struct registers {
+    uint32_t gs, fs, es, ds;                           // Pushed manually
+    uint32_t edi, esi, ebp, esp, ebx, edx, ecx, eax;   // Pushed by pusha
+    uint32_t int_no, err_code;                         // Pushed manually
+    uint32_t eip, cs, eflags, useresp, ss;             // Pushed automatically by CPU
+} registers_t;
+
+int32_t sys_vga_text_write(char* buf);
+
+int32_t syscall(registers_t* regs) {
+    switch(regs->eax) {
+        case 1: {
+            return sys_vga_text_write((char*)regs->ebx);
+        }
+        default:
+            return -1;
+    }
+}
+
+int32_t sys_vga_text_write(char* buf) {
+    kprintf(buf);
+    return 0;
+}

kernel/syscall_stubs.S

@@ -0,0 +1,36 @@
+.code32 
+.global syscall_handler
+.extern syscall
+syscall_handler: 
+    cli
+
+    push $0
+    push $0x80
+
+    pusha
+
+    push %ds
+    push %es
+    push %fs
+    push %gs
+
+    mov $0x10, %ax               
+    mov %ax, %ds
+    mov %ax, %es
+    mov %ax, %fs
+    mov %ax, %gs
+    
+    push %esp
+    call syscall
+    add $4, %esp
+    
+    mov 28(%esp), %eax
+
+    pop %gs
+    pop %fs
+    pop %es
+    pop %ds
+
+    popa
+    add $8, %esp
+    iret