diff options
Diffstat (limited to 'MdePkg/Library/BaseLib/X64/Thunk16.S')
| -rw-r--r-- | MdePkg/Library/BaseLib/X64/Thunk16.S | 21 |
1 files changed, 19 insertions, 2 deletions
diff --git a/MdePkg/Library/BaseLib/X64/Thunk16.S b/MdePkg/Library/BaseLib/X64/Thunk16.S index a1af512..3f94759 100644 --- a/MdePkg/Library/BaseLib/X64/Thunk16.S +++ b/MdePkg/Library/BaseLib/X64/Thunk16.S @@ -264,7 +264,23 @@ ASM_PFX(InternalAsmThunk16): shll $12,%eax # segment address in high order 16 bits
lea (_BackFromUserCode - ASM_PFX(m16Start))(%rdx), %ax
stosl # [edi] <- return address of user code
- sgdt (SavedGdt - SavedCr4)(%rcx)
+ sgdt 0x60(%rsp) # save GDT stack in argument space
+ movzwq 0x60(%rsp), %r10 # r10 <- GDT limit
+ lea ((ASM_PFX(InternalAsmThunk16) - SavedCr4) + 0xf)(%rcx), %r11
+ andl $0xfffffff0, r11 # r11 <- 16-byte aligned shadowed GDT table in real mode buffer
+
+ movw %r10w, (SavedGdt - SavedCr4)(%rcx) # save the limit of shadowed GDT table
+ movq %r11, (SavedGdt - SavedCr4 + 0x2)(%rcx) # save the base address of shadowed GDT table
+
+ movq 0x62(%rsp) ,%rsi # rsi <- the original GDT base address
+ xchg %r10, %rcx # save rcx to r10 and initialize rcx to be the limit of GDT table
+ incq %rcx # rcx <- the size of memory to copy
+ xchg %r11, %rdi # save rdi to r11 and initialize rdi to the base address of shadowed GDT table
+ rep
+ movsb # perform memory copy to shadow GDT table
+ movq %r10, %rcx # restore the orignal rcx before memory copy
+ movq %r11, %rdi # restore the original rdi before memory copy
+
sidt 0x50(%rsp)
movq %cr0, %rax
movl %eax, (SavedCr0 - SavedCr4)(%rcx)
@@ -288,7 +304,8 @@ ASM_PFX(InternalAsmThunk16): .byte _EntryPoint - SavedCr4
L_RetFromRealMode:
popfq
- lidt 0x50(%rsp)
+ lgdt 0x60(%rsp) # restore protected mode GDTR
+ lidt 0x50(%rsp) # restore protected mode IDTR
lea -IA32_REGS_SIZE(%rbp), %eax
.byte 0x0f, 0xa9 # pop gs
.byte 0x0f, 0xa1 # pop fs
|