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#
# Copyright (c) 2010, Intel Corporation. All rights reserved.<BR>
# This program and the accompanying materials
# are licensed and made available under the terms and conditions of the BSD License
# which accompanies this distribution. The full text of the license may be found at
# http://opensource.org/licenses/bsd-license.php
#
# THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
# WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
#
#
# Module Name:
#
# AsmDispatchExecute.asm
#
# Abstract:
#
# This is the assembly code to transition from long mode to compatibility mode to execute 32-bit code and then
# transit back to long mode.
#
#-------------------------------------------------------------------------------
#----------------------------------------------------------------------------
# Procedure: AsmExecute32BitCode
#
# Input: None
#
# Output: None
#
# Prototype: EFI_STATUS
# AsmExecute32BitCode (
# IN UINT64 Function,
# IN UINT64 Param1,
# IN UINT64 Param2,
# IN IA32_DESCRIPTOR *InternalGdtr
# );
#
#
# Description: A thunk function to execute 32-bit code in long mode.
#
#----------------------------------------------------------------------------
ASM_GLOBAL ASM_PFX(AsmExecute32BitCode)
ASM_PFX(AsmExecute32BitCode):
#
# save orignal GDTR and CS
#
movq %ds, %rax
push %rax
movq %cs, %rax
push %rax
subq $0x10, %rsp
sgdt (%rsp)
#
# load internal GDT
#
lgdt (%r9)
#
# Save general purpose register and rflag register
#
pushfq
push %rdi
push %rsi
push %rbp
push %rbx
#
# save CR3
#
movq %cr3, %rax
movq %rax, %rbp
#
# Prepare the CS and return address for the transition from 32-bit to 64-bit mode
#
movq $0x10, %rax # load long mode selector
shl $32, %rax
lea ReloadCS(%rip), %r9 #Assume the ReloadCS is under 4G
orq %r9, %rax
push %rax
#
# Save parameters for 32-bit function call
#
movq %r8, %rax
shl $32, %rax
orq %rdx, %rax
push %rax
#
# save the 32-bit function entry and the return address into stack which will be
# retrieve in compatibility mode.
#
lea ReturnBack(%rip), %rax #Assume the ReloadCS is under 4G
shl $32, %rax
orq %rcx, %rax
push %rax
#
# let rax save DS
#
movq $0x18, %rax
#
# Change to Compatible Segment
#
movq $8, %rcx # load compatible mode selector
shl $32, %rcx
lea Compatible(%rip), %rdx # assume address < 4G
orq %rdx, %rcx
push %rcx
retf
Compatible:
# reload DS/ES/SS to make sure they are correct referred to current GDT
movw %ax, %ds
movw %ax, %es
movw %ax, %ss
#
# Disable paging
#
movq %cr0, %rcx
btc $31, %ecx
movq %rcx, %cr0
#
# Clear EFER.LME
#
movl $0xC0000080, %ecx
rdmsr
btc $8, %eax
wrmsr
# Now we are in protected mode
#
# Call 32-bit function. Assume the function entry address and parameter value is less than 4G
#
pop %rax # Here is the function entry
#
# Now the parameter is at the bottom of the stack, then call in to IA32 function.
#
jmp *%rax
ReturnBack:
pop %rcx # drop param1
pop %rcx # drop param2
#
# restore CR4
#
movq %cr4, %rax
bts $5, %eax
movq %rax, %cr4
#
# restore CR3
#
movl %ebp, %eax
movq %rax, %cr3
#
# Set EFER.LME to re-enable ia32-e
#
movl $0xC0000080, %ecx
rdmsr
bts $8, %eax
wrmsr
#
# Enable paging
#
movq %cr0, %rax
bts $31, %eax
mov %rax, %cr0
# Now we are in compatible mode
#
# Reload cs register
#
retf
ReloadCS:
#
# Now we're in Long Mode
#
#
# Restore C register and eax hold the return status from 32-bit function.
# Note: Do not touch rax from now which hold the return value from IA32 function
#
pop %rbx
pop %rbp
pop %rsi
pop %rdi
popfq
#
# Switch to orignal GDT and CS. here rsp is pointer to the orignal GDT descriptor.
#
lgdt (%rsp)
#
# drop GDT descriptor in stack
#
addq $0x10, %rsp
#
# switch to orignal CS and GDTR
#
pop %r9 # get CS
shl $32, %r9 # rcx[32..47] <- Cs
lea ReturnToLongMode(%rip), %rcx
orq %r9, %rcx
push %rcx
retf
ReturnToLongMode:
#
# Reload original DS/ES/SS
#
pop %rcx
movq %rcx, %ds
movq %rcx, %es
movq %rcx, %ss
ret
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