/*
 * COPYRIGHT:   See COPYING in the top level directory
 * PROJECT:     ReactOS system libraries
 * FILE:        lib/kernel32/thread/i386/fiber.S
 * PURPOSE:     Fiber context switch code for the x86 architecture
 * PROGRAMMERS: Alex Ionescu (alex@relsoft.net)
 *              KJK::Hyperion <noog@libero.it>
 */

#include <ndk/asm.h>

#define CONTEXT_FULL                    0x10007
#define CONTEXT_FLOATING_POINT          0xF

.globl _SwitchToFiber@4
.intel_syntax noprefix

_SwitchToFiber@4:
    /* Get the TEB */
    mov edx, fs:[KGDT_R3_TEB]
    
    /* Get the Fiber */
    mov eax, [edx+TEB_FIBER_DATA]
    
    /* Save the non-volatile registers */
    mov [eax+FIBER_CONTEXT_EBX], ebx
    mov [eax+FIBER_CONTEXT_ESI], esi
    mov [eax+FIBER_CONTEXT_EDI], edi
    mov [eax+FIBER_CONTEXT_EBP], ebp
    
    /* Check if we're to save FPU State */
    cmp dword ptr [eax+FIBER_CONTEXT_FLAGS], CONTEXT_FULL + CONTEXT_FLOATING_POINT
    jnz NoFpuStateSave
    
    /* Save the FPU State (Status and Control)*/
    fstsw [eax+FIBER_CONTEXT_FLOAT_SAVE_STATUS_WORD]
    fstcw [eax+FIBER_CONTEXT_FLOAT_SAVE_CONTROL_WORD]
    
    /* Check if the CPU supports SIMD MXCSR State Save */
    cmp byte ptr [PROCESSOR_FEATURE_FXSR], 0
    jnz NoFpuStateSave
    stmxcsr [eax+FIBER_CONTEXT_DR6]
    
NoFpuStateSave:

    /* Save stack since we're not touching it anymore */
    mov [eax+FIBER_CONTEXT_ESP], esp
    
    /* Transfer some data from the TEB */
    mov ecx, [edx+TEB_FLS_DATA]
    mov [eax+FIBER_FLS_DATA], ecx
    mov ecx, [edx+TEB_ACTIVATION_CONTEXT_STACK_POINTER]
    mov [eax+FIBER_ACTIVATION_CONTEXT_STACK], ecx
    
    /* Transfer some data related to the Stack */
    mov ecx, [edx+TEB_EXCEPTION_LIST]
    mov [eax+FIBER_EXCEPTION_LIST], ecx
    mov ecx, [edx+TEB_STACK_LIMIT]
    mov [eax+FIBER_STACK_LIMIT], ecx
    mov ecx, [edx+TEB_GUARANTEED_STACK_BYTES]
    mov [eax+FIBER_GUARANTEED_STACK_BYTES], ecx
    
    /* Switch to the new fiber */
    mov ecx, [esp+4]
    mov [edx+TEB_FIBER_DATA], ecx
    
    /* Switch Fiber Data */
    mov esi, [ecx+FIBER_EXCEPTION_LIST]
    mov [edx+TEB_EXCEPTION_LIST], esi
    mov esi, [ecx+FIBER_STACK_BASE]
    mov [edx+TEB_STACK_BASE], esi
    mov esi, [ecx+FIBER_STACK_LIMIT]
    mov [edx+TEB_STACK_LIMIT], esi
    mov esi, [ecx+FIBER_DEALLOCATION_STACK]
    mov [edx+TEB_DEALLOCATION_STACK], esi
    mov esi, [ecx+FIBER_GUARANTEED_STACK_BYTES]
    mov [edx+TEB_GUARANTEED_STACK_BYTES], esi
    mov esi, [ecx+FIBER_ACTIVATION_CONTEXT_STACK]
    mov [edx+TEB_ACTIVATION_CONTEXT_STACK_POINTER], esi
    
    /* Restore FPU State */
    cmp dword ptr [eax+FIBER_CONTEXT_FLAGS], CONTEXT_FULL + CONTEXT_FLOATING_POINT
    jnz NoFpuStateRestore
    
    /* Check if the Status Word Changed */
    mov esi, [eax+FIBER_CONTEXT_FLOAT_SAVE_STATUS_WORD]
    cmp si, word ptr [ecx+FIBER_CONTEXT_FLOAT_SAVE_STATUS_WORD]
    jnz StatusWordChanged
    
    /* Check if the Control Word Changed */
    mov esi, [eax+FIBER_CONTEXT_FLOAT_SAVE_CONTROL_WORD]
    cmp si, word ptr [ecx+FIBER_CONTEXT_FLOAT_SAVE_CONTROL_WORD]
    jz ControlWordEqual
    
StatusWordChanged:

    /* Load the new one */
    mov word ptr [ecx+FIBER_CONTEXT_FLOAT_SAVE_TAG_WORD], 0xFFFF
    fldenv [ecx+FIBER_CONTEXT_FLOAT_SAVE_CONTROL_WORD]
    
ControlWordEqual:

    /* Load the new one */
    cmp byte ptr [PROCESSOR_FEATURE_FXSR], 0
    jnz NoFpuStateRestore
    ldmxcsr [ecx+FIBER_CONTEXT_DR6]
    
NoFpuStateRestore:

    /* Restore non-volatile registers */
    mov esi, [ecx+FIBER_CONTEXT_ESI]
    mov edi, [ecx+FIBER_CONTEXT_EDI]
    mov ebx, [ecx+FIBER_CONTEXT_EBX]
    mov ebp, [ecx+FIBER_CONTEXT_EBP]
    mov esp, [ecx+FIBER_CONTEXT_ESP]
    
    /* Restore FLS Data */
    mov eax, [ecx+FIBER_FLS_DATA]
    mov [edx+TEB_FLS_DATA], eax

    /* Return */
    ret 4
    
/* EOF */