Save segment registers on stack in case the thunk code assembly calls CF9 soft reset...

[mirror_edk2.git] / MdePkg / Library / BaseLib / X64 / Thunk16.asm

diff --git a/MdePkg/Library/BaseLib/X64/Thunk16.asm b/MdePkg/Library/BaseLib/X64/Thunk16.asm
index 642310869b6fe6ec6574f56ed387f054dd9cab03..cef63d98e1f41612574c124620e5ed545090a155 100644 (file)
--- a/MdePkg/Library/BaseLib/X64/Thunk16.asm
+++ b/MdePkg/Library/BaseLib/X64/Thunk16.asm
@@ -1,6 +1,9 @@
+\r
+#include "BaseLibInternals.h"\r
+\r
 ;------------------------------------------------------------------------------\r
 ;\r
-; Copyright (c) 2006, Intel Corporation\r
+; Copyright (c) 2006 - 2008, Intel Corporation\r
 ; All rights reserved. This program and the accompanying materials\r
 ; are licensed and made available under the terms and conditions of the BSD License\r
 ; which accompanies this distribution.  The full text of the license may be found at\r
@@ -66,6 +69,14 @@ SavedGdt    LABEL   FWORD
 ; by user code. It will be shadowed to somewhere in memory below 1MB.\r
 ;------------------------------------------------------------------------------\r
 _BackFromUserCode   PROC\r
+    ;\r
+    ; The order of saved registers on the stack matches the order they appears\r
+    ; in IA32_REGS structure. This facilitates wrapper function to extract them\r
+    ; into that structure.\r
+    ;\r
+    ; Some instructions for manipulation of segment registers have to be written\r
+    ; in opcode since 64-bit MASM prevents accesses to those registers.\r
+    ;\r
     DB      16h                         ; push ss\r
     DB      0eh                         ; push cs\r
     DB      66h\r
@@ -115,7 +126,7 @@ SavedCr4    DD      ?
     ;\r
     ; rdi in the instruction below is indeed bx in 16-bit code\r
     ;\r
-    DB      66h, 2eh\r
+    DB      66h, 2eh                    ; 2eh is "cs:" segment override\r
     lgdt    fword ptr [rdi + (SavedGdt - @Base)]\r
     DB      66h\r
     mov     ecx, 0c0000080h\r
@@ -129,9 +140,11 @@ SavedCr0    DD      ?
 @64Eip      DD      ?\r
 SavedCs     DW      ?\r
 @64BitCode:\r
-    DB      48h, 0b8h                   ; mov rax, imm64\r
-SavedRip    DQ      ?\r
-    jmp     rax                         ; return to caller\r
+    db      090h \r
+    db      067h, 0bch                 ; mov esp, imm32\r
+SavedSp     DD   ?                     ; restore stack\r
+    nop\r
+    ret\r
 _BackFromUserCode   ENDP\r
 \r
 _EntryPoint DD      _ToUserCode - m16Start\r
@@ -160,14 +173,14 @@ _ToUserCode PROC
     mov     cr4, rbp\r
     mov     ss, esi                     ; set up 16-bit stack segment\r
     mov     sp, bx                      ; set up 16-bit stack pointer\r
-    DB      66h\r
+    DB      66h                         ; make the following call 32-bit\r
     call    @Base                       ; push eip\r
 @Base:\r
     pop     bp                          ; ebp <- address of @Base\r
     push    [esp + sizeof (IA32_REGS) + 2]\r
-    lea     eax, [rsi + (@RealMode - @Base)]\r
+    lea     eax, [rsi + (@RealMode - @Base)]    ; rsi is "bp" in 16-bit code\r
     push    rax\r
-    retf\r
+    retf                                ; execution begins at next instruction\r
 @RealMode:\r
     DB      66h, 2eh                    ; CS and operand size override\r
     lidt    fword ptr [rsi + (_16Idtr - @Base)]\r
@@ -178,7 +191,7 @@ _ToUserCode PROC
     pop     gs\r
     popf                                ; popfd\r
     lea     sp, [esp + 4]               ; skip high order 32 bits of EFlags\r
-    DB      66h\r
+    DB      66h                         ; make the following retf 32-bit\r
     retf                                ; transfer control to user code\r
 _ToUserCode ENDP\r
 \r
@@ -220,9 +233,13 @@ GDT_SIZE = $ - _NullSeg
 ;   );\r
 ;------------------------------------------------------------------------------\r
 InternalAsmThunk16  PROC    USES    rbp rbx rsi rdi\r
-    mov     r10d, ds\r
-    mov     r11d, es\r
-    mov     r9d, ss\r
+    mov     rbx, ds\r
+    push    rbx          ; Save ds segment register on the stack\r
+    mov     rbx, es\r
+    push    rbx          ; Save es segment register on the stack\r
+    mov     rbx, ss\r
+    push    rbx          ; Save ss segment register on the stack\r
+    \r
     push    fs\r
     push    gs\r
     mov     rsi, rcx\r
@@ -238,11 +255,11 @@ InternalAsmThunk16  PROC    USES    rbp rbx rsi rdi
     lea     ecx, [rdx + (SavedCr4 - m16Start)]\r
     mov     eax, edx                    ; eax <- transition code address\r
     and     edx, 0fh\r
-    shl     eax, 12\r
-    lea     ax, [rdx + (_BackFromUserCode - m16Start)]\r
+    shl     eax, 12                     ; segment address in high order 16 bits\r
+    lea     ax, [rdx + (_BackFromUserCode - m16Start)]  ; offset address\r
     stosd                               ; [edi] <- return address of user code\r
     sgdt    fword ptr [rcx + (SavedGdt - SavedCr4)]\r
-    sidt    fword ptr [rsp + 38h]       ; save IDT stack in argument space\r
+    sidt    fword ptr [rsp + 50h]       ; save IDT stack in argument space\r
     mov     rax, cr0\r
     mov     [rcx + (SavedCr0 - SavedCr4)], eax\r
     and     eax, 7ffffffeh              ; clear PE, PG bits\r
@@ -257,21 +274,23 @@ InternalAsmThunk16  PROC    USES    rbp rbx rsi rdi
     pushfq\r
     lea     edx, [rdx + DATA16 - DATA32]\r
     lea     r8, @RetFromRealMode\r
-    mov     [rcx + (SavedRip - SavedCr4)], r8\r
+    push    r8\r
     mov     r8d, cs\r
     mov     [rcx + (SavedCs - SavedCr4)], r8w\r
-    mov     r8, rsp\r
+    mov     [rcx + (SavedSp - SavedCr4)], esp\r
     jmp     fword ptr [rcx + (_EntryPoint - SavedCr4)]\r
 @RetFromRealMode:\r
-    mov     rsp, r8\r
     popfq\r
-    lidt    fword ptr [rsp + 38h]       ; restore protected mode IDTR\r
+    lidt    fword ptr [rsp + 50h]       ; restore protected mode IDTR\r
     lea     eax, [rbp - sizeof (IA32_REGS)]\r
     pop     gs\r
     pop     fs\r
-    mov     ss, r9d\r
-    mov     es, r11d\r
-    mov     ds, r10d\r
+    pop     rbx\r
+    mov     ss, rbx\r
+    pop     rbx\r
+    mov     es, rbx\r
+    pop     rbx\r
+    mov     ds, rbx\r
     ret\r
 InternalAsmThunk16  ENDP\r
 \r