preparing for multitasking

2 files changed, 39 insertions, 0 deletions

diff --git a/asm/copy_page_physical.asm b/asm/copy_page_physical.asm
new file mode 100644
index 0000000..f8d3af1
--- /dev/null
+++ b/asm/copy_page_physical.asm
@@ -0,0 +1,33 @@
+[bits 32]
+
+global copy_page_physical
+copy_page_physical:
+   push ebx              ; According to __cdecl, we must preserve the contents of EBX.
+   pushf                 ; push EFLAGS, so we can pop it and reenable interrupts
+                         ; later, if they were enabled anyway.
+   cli                   ; Disable interrupts, so we aren't interrupted.
+                         ; Load these in BEFORE we disable paging!
+   mov ebx, [esp+12]     ; Source address
+   mov ecx, [esp+16]     ; Destination address
+
+   mov edx, cr0          ; Get the control register...
+   and edx, 0x7fffffff   ; and...
+   mov cr0, edx          ; Disable paging.
+
+   mov edx, 1024         ; 1024*4bytes = 4096 bytes to copy
+
+.loop:
+   mov eax, [ebx]        ; Get the word at the source address
+   mov [ecx], eax        ; Store it at the dest address
+   add ebx, 4            ; Source address += sizeof(word)
+   add ecx, 4            ; Dest address += sizeof(word)
+   dec edx               ; One less word to do
+   jnz .loop
+
+   mov edx, cr0          ; Get the control register again
+   or  edx, 0x80000000   ; and...
+   mov cr0, edx          ; Enable paging.
+
+   popf                  ; Pop EFLAGS back.
+   pop ebx               ; Get the original value of EBX back.
+   ret
diff --git a/asm/read_eip.asm b/asm/read_eip.asm
new file mode 100644
index 0000000..3341943
--- /dev/null
+++ b/asm/read_eip.asm
@@ -0,0 +1,6 @@
+; http://www.jamesmolloy.co.uk/tutorial_html/9.-Multitasking.html
+[bits 32]
+global read_eip
+read_eip:
+      pop eax
+       jmp eax