struggling with vmem

1 files changed, 39 insertions, 0 deletions

diff --git a/asm/asm_usermode.S b/asm/asm_usermode.S
new file mode 100644
index 0000000..a07f480
--- /dev/null
+++ b/asm/asm_usermode.S
@@ -0,0 +1,39 @@
+.global asm_usermode
+
+asm_usermode:
+
+	mov 0x4(%esp),%edx    //get adress of passed : void func()
+			      //to be called in ring 3
+
+	// 0x23 is user data segment (|2 low bits)
+	// 0x1b is user code segment (|2 low bits)
+
+	// set segment registers
+        mov $0x23, %ax
+        mov %ax, %ds
+        mov %ax, %es
+        mov %ax, %fs
+        mov %ax, %gs
+
+	// ss is handled by iret
+                 
+        mov %esp, %eax
+
+        pushl $0x23 // user data segment
+        //pushl $0x8fff000-3*32 //%eax  // current stack
+        pushl $0xe0000000-3*32 //%eax  // current stack (3 values will be poped) we subst 4 to align
+        pushf	    // 
+
+        // http://x86.renejeschke.de/html/file_module_x86_id_145.html
+        //mov $0x200, %eax
+	//push %eax	    // eflags image
+        pushl $0x1B	    // return code segment selector
+        push %edx	    // return instruction pointer
+
+        iret
+
+	jmp . // never to be reached
+
+
+ 
+