christoph/lecture-operating-system-development
1
Fork 0
Code Activity

use the stack for regs in thread_switch

Browse Source
This commit is contained in:
Christoph Urlacher
2022-07-23 18:40:16 +02:00
parent cd26464052
commit 70876f1a06
1 changed files with 22 additions and 137 deletions
Download Patch File Download Diff File Expand all files Collapse all files

159
c_os/kernel/threads/Thread.asm
View File

@ -49,20 +49,6 @@ Thread_start:
;; == Low address ==
popf
;; == High address ==
;; *OBJECT
;; 0x13115
;; *KICKOFF
;; EAX
;; ECX
;; EDX
;; EBX
;; ESP
;; EBP
;; ESI
;; SP --> EDI
;; == Low address ==
popa
;; == High address ==
;; *OBJECT
@ -80,144 +66,43 @@ Thread_switch:
; *
;; NOTE: The thread switching works like this:
;; 1. Prev thread is running, pit interrupt triggers preemption
;; 2. CPU switches to interrupt/scheduler stack and calls Thread_switch,
;; two arguments and the return address are pushed before the call,
;; the return address leads back to the prev thread
;; 3. Prev registers are pushed to prev stack
;; 4. Next registers are popped from next stack, the esp now points
;; to the return address it pointed to when the next thread was
;; exited in the past
;; 5. Return follows the return address to the next stack
;; 1. Prev thread is running, pit interrupt triggers preemption, interrupt handler called
;; 2. Prev registers are pushed to prev stack after the return address
;; 3. Switch to next stack
;; 3. Registers are popped from stack, the esp now points
;; to the return address (that was written to the stack when it
;; was switched from)
;; 4. Return follows the return address to resume normal stack execution
;; NOTE: New code with pusha/popa
;; 1. Backup the current esp to the prev stack
;; 2. Switch to the prev stack and pusha, pushf
;; 3. Update the prev stack esp so popf, popa works on
;; the correct address
;; 4. Jump back to the scheduler stack with the esp from 1.
;; 5. Jump to the next stack and popf, popa
push eax ; Backup eax because we use it later to temporarily store the esp to jump back to
; the interrupt stack
;; == High address == ; Scheduler stack
;; ESP_NEXT
;; + 0x8 *ESP_PREV
;; RET ADDR
;; SP --> EAX
;; == Low address ==
mov eax, [esp + 0x8] ; Could probably leave this out as this value already is in eax because it' the first
; function parameter
mov eax, [eax] ; EAX points to the address of the thread's eax beacause we called with a pointer
;; == High address == ; Previous thread stack (thread that was running when the interrupt came)
;; OLD
;; THREAD
;; STACK
;; EAX -> RET ADDR
;; == Low address ==
sub eax, 0x28
mov [eax], esp ; Current esp to old thread stack, 0x24 is the amount pusha, pushf change the esp
; We save it, push the current registers to the old threads stack, return and restore
;; == High address ==
;; OLD
;; THREAD
;; STACK
;; 0x0 RET ADDR
;; 0x4
;; 0x8
;; 0xc
;; 0x10
;; 0x14
;; 0x18
;; 0x1c
;; 0x20
;; 0x24
;; EAX -> ESP (Points not to RET ADDR but the EAX we pushed as backup!!!)
;; == Low address ==
pop eax ; ESP still points to the EAX we pushed before
;; == High address ==
;; ESP_NEXT
;; *ESP_PREV
;; SP --> RET ADDR
;; == Low address ==
mov esp, [esp + 0x4]
mov esp, [esp]
;; == High address ==
;; OLD
;; THREAD
;; STACK
;; SP --> RET ADDR
;; 0x4
;; 0x8
;; 0xc
;; 0x10
;; 0x14
;; 0x18
;; 0x1c
;; 0x20
;; 0x24
;; 0x28 ESP
;; == Low address ==
pusha ; Save current registers to stack
pusha
pushf
;; == High address ==
;; OLD
;; THREAD
;; STACK
;; RET ADDR
;; 0x4 EAX
;; 0x8 ECX
;; 0xc EDX
;; 0x10 EBX
;; 0x14 ESP
;; 0x18 EBP
;; 0x1c ESI
;; 0x20 EDI
;; + 0x2c ESP_NEXT
;; + 0x28 *ESP_PREV
;; + 0x24 RET ADDR
;; EAX
;; ECX
;; EDX
;; EBX
;; ESP
;; EBP
;; ESI
;; EDI
;; SP --> EFLAGS
;; 0x28 ESP
;; == Low address ==
sub esp, 0x4
pop esp ; The POP ESP instruction increments the stack pointer (ESP)
add esp, 0x4 ; before data at the old top of stack is written into the destination.
;; == High address ==
;; ESP_NEXT
;; *ESP_PREV
;; SP --> RET ADDR
;; == Low address ==
mov eax, [esp + 0x4] ; EAX is backed up and free to use now
mov ebx, eax ; Duplicate because we dereference eax later
mov eax, [eax] ; EAX points to prev stack
sub eax, 0x24 ; EAX points to EFLAGS that we pushf'd on prev stack
;; == High address ==
;; OLD
;; THREAD
;; STACK
;; RET ADDR
;; 0x4 EAX
;; 0x8 ECX
;; 0xc EDX
;; 0x10 EBX
;; 0x14 ESP
;; 0x18 EBP
;; 0x1c ESI
;; 0x20 EDI
;; EAX -> EFLAGS
;; == Low address ==
mov [ebx], eax ; Change prev thread's esp to point to the new bottom of stack
; so popf, popa works when prev thread becomes active again
mov eax, [esp + 0x28] ; Point to *ESP_PREV (Address)
mov [eax], esp ; Update thread esp variable
;; ============================================================
mov esp, [esp + 0x8] ; Move to next coroutines stack
mov esp, [esp + 0x2c] ; Move to next coroutines stack
;; == High address ==
;; NEW
;; THREAD