Remove assumption that the transition code for transitioning from 64-bit to 32-bit mode is 64 bytes. Instead compute the size based on the implementation in the ASM file.
Update logic to align new 32-bit stack on a 4 byte boundary Update logic to prevent one slot overlap between the transition code and the new stack. git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@10133 6f19259b-4bc3-4df7-8a09-765794883524
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@@ -38,20 +38,23 @@ InternalX86DisablePaging64 PROC
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cli
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lea rsi, @F ; rsi <- The start address of transition code
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mov edi, [rsp + 28h] ; rdi <- New stack
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sub edi, 64 ; rdi <- use 64 byte in stack to hold transition code
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mov r10d, edi ; r10 <- The start address of transicition code below 4G
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lea rax, mTransitionEnd ; rax <- end of transition code
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sub rax, rsi ; rax <- The size of transition piece code
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add rax, 4 ; Round RAX up to the next 4 byte boundary
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and rax, 0fffffffch
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sub rdi, rax ; rdi <- Use stack to hold transition code
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mov r10d, edi ; r10 <- The start address of transicition code below 4G
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push rcx ; save rcx to stack
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mov rcx, rax ; rcx <- The size of transition piece code
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rep movsb ; copy transition code to (new stack - 64byte) below 4G
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rep movsb ; copy transition code to top of new stack which must be below 4GB
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pop rcx ; restore rcx
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mov esi, r8d
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mov edi, r9d
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mov eax, [rsp + 28h] ; eax <- New Stack
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mov eax, r10d ; eax <- start of the transition code on the stack
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sub eax, 4 ; eax <- One slot below transition code on the stack
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push rcx ; push Cs to stack
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push r10
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push r10 ; push address of tansition code on stack
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DB 48h ; prefix to composite "retq" with next "retf"
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retf ; Use far return to load CS register from stack
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@@ -59,10 +62,10 @@ InternalX86DisablePaging64 PROC
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@@:
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mov esp, eax ; set up new stack
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mov rax, cr0
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btr eax, 31
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mov cr0, rax ; disable paging
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mov rbx, rdx ; save EntryPoint to rbx, for rdmsr will overwrite rdx
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btr eax, 31 ; Clear CR0.PG
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mov cr0, rax ; disable paging and caches
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mov ebx, edx ; save EntryPoint to rbx, for rdmsr will overwrite rdx
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mov ecx, 0c0000080h
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rdmsr
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and ah, NOT 1 ; clear LME
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