[prefix] Use 16-bit protected mode for access to high memory
Flat real mode works perfectly on real hardware, but seems to cause problems for some hypervisors. Revert to using 16-bit protected mode (and returning to real mode with 4GB limits, so as not to break PMM BIOSes). Allow the code specific to the .mrom format to continue to assume that flat real mode works, since this format is specific to real hardware. Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
parent
21d6f9cd8e
commit
a84e15234a
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@ -24,6 +24,9 @@ FILE_LICENCE ( GPL2_OR_LATER )
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/* Image compression enabled */
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#define COMPRESS 1
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/* Protected mode flag */
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#define CR0_PE 1
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/*****************************************************************************
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* Utility function: print character (with LF -> LF,CR translation)
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*
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@ -229,16 +232,186 @@ print_kill_line:
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* None
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****************************************************************************
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*/
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#if ! COMPRESS
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.section ".prefix.lib", "awx", @progbits
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.code16
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copy_bytes:
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pushl %ecx
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pushl %ecx
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rep addr32 movsb
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popl %ecx
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popl %ecx
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ret
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.size copy_bytes, . - copy_bytes
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#endif /* COMPRESS */
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.size copy_bytes, . - copy_bytes
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/****************************************************************************
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* zero_bytes
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*
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* Zero bytes
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*
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* Parameters:
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* %ds:esi : source address
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* %es:edi : destination address
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* %ecx : length
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* Returns:
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* %ds:esi : next source address
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* %es:edi : next destination address
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* Corrupts:
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* None
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****************************************************************************
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*/
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.section ".prefix.lib", "awx", @progbits
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.code16
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zero_bytes:
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pushl %ecx
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pushw %ax
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xorw %ax, %ax
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rep addr32 stosb
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popw %ax
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popl %ecx
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ret
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.size zero_bytes, . - zero_bytes
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/****************************************************************************
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* process_bytes
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*
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* Call memcpy()-like function
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*
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* Parameters:
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* %esi : source physical address
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* %edi : destination physical address
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* %ecx : length
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* %bx : memcpy()-like function to call, passing parameters:
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* %ds:esi : source address
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* %es:edi : destination address
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* %ecx : length
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* and returning:
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* %ds:esi : next source address
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* %es:edi : next destination address
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* Returns:
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* %esi : next source physical address
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* %edi : next destination physical address
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* Corrupts:
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* None
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****************************************************************************
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*/
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.section ".prefix.lib", "awx", @progbits
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.code16
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process_bytes:
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#ifndef KEEP_IT_REAL
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/* Preserve registers */
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pushfw
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pushl %eax
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pushl %ebp
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/* Construct GDT on stack (since .prefix may not be writable) */
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.equ PM_DS, 0x18 /* Flat data segment */
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pushl $0x008f9300
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pushl $0x0000ffff
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.equ PM_SS, 0x10 /* Stack segment based at %ss:0000 */
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pushl $0x008f0930
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pushw %ss
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pushw $0xffff
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.equ PM_CS, 0x08 /* Code segment based at %cs:0000 */
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pushl $0x008f09b0
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pushw %cs
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pushw $0xffff
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pushl $0 /* Base and length */
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pushw %ss
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pushw $0x1f
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movzwl %sp, %ebp
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shll $4, 0x02(%bp)
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addl %ebp, 0x02(%bp)
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shll $4, 0x0a(%bp)
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shll $4, 0x12(%bp)
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subw $8, %sp
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sgdt -8(%bp)
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/* Switch to protected mode */
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pushw %gs
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pushw %fs
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pushw %es
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pushw %ds
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pushw %ss
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pushw %cs
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pushw $2f
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cli
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data32 lgdt (%bp)
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movl %cr0, %eax
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orb $CR0_PE, %al
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movl %eax, %cr0
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ljmp $PM_CS, $1f
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1: movw $PM_SS, %ax
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movw %ax, %ss
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movw $PM_DS, %ax
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movw %ax, %ds
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movw %ax, %es
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movw %ax, %fs
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movw %ax, %gs
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/* Call memcpy()-like function */
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call *%bx
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/* Return to (flat) real mode */
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movl %cr0, %eax
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andb $0!CR0_PE, %al
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movl %eax, %cr0
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lret
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2: /* lret will ljmp to here */
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popw %ss
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popw %ds
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popw %es
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popw %fs
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popw %gs
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/* Restore GDT */
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data32 lgdt -8(%bp)
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addw $( 8 /* saved GDT */ + ( PM_DS + 8 ) /* GDT on stack */ ), %sp
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/* Restore registers and return */
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popl %ebp
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popl %eax
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popfw
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ret
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#else /* KEEP_IT_REAL */
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/* Preserve registers */
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pushl %eax
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pushw %ds
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pushw %es
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/* Convert %esi and %edi to %ds:esi and %es:edi */
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shrl $4, %esi
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movw %si, %ds
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xorw %si, %si
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shll $4, %esi
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shrl $4, %edi
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movw %di, %es
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xorw %di, %di
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shll $4, %edi
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/* Call memcpy()-like function */
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call *%bx
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/* Convert %ds:esi and %es:edi back to physical addresses */
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xorl %eax, %eax
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movw %ds, %cx
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shll $4, %eax
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addl %eax, %esi
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xorl %eax, %eax
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movw %es, %cx
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shll $4, %eax
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addl %eax, %edi
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/* Restore registers and return */
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popw %es
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popw %ds
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popl %eax
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ret
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#endif /* KEEP_IT_REAL */
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.size process_bytes, . - process_bytes
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/****************************************************************************
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* install_block
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@ -261,35 +434,22 @@ copy_bytes:
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.code16
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install_block:
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/* Preserve registers */
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pushw %ds
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pushw %es
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pushl %ecx
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/* Convert %esi and %edi to %ds:esi and %es:edi */
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shrl $4, %esi
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movw %si, %ds
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xorw %si, %si
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shll $4, %esi
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shrl $4, %edi
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movw %di, %es
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xorw %di, %di
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shll $4, %edi
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pushw %bx
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/* Decompress (or copy) source to destination */
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#if COMPRESS
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/* Decompress source to destination */
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call decompress16
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movw $decompress16, %bx
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#else
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/* Copy source to destination */
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call copy_bytes
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movw $copy_bytes, %bx
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#endif
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call process_bytes
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/* Zero .bss portion */
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negl %ecx
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addl %edx, %ecx
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pushw %ax
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xorw %ax, %ax
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rep addr32 stosb
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popw %ax
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movw $zero_bytes, %bx
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call process_bytes
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/* Round up %esi and %edi to start of next blocks */
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addl $0xf, %esi
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@ -297,20 +457,9 @@ install_block:
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addl $0xf, %edi
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andl $~0xf, %edi
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/* Convert %ds:esi and %es:edi back to physical addresses */
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xorl %ecx, %ecx
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movw %ds, %cx
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shll $4, %ecx
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addl %ecx, %esi
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xorl %ecx, %ecx
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movw %es, %cx
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shll $4, %ecx
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addl %ecx, %edi
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/* Restore registers and return */
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popw %bx
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popl %ecx
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popw %es
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popw %ds
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ret
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.size install_block, . - install_block
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@ -612,11 +761,10 @@ payload_death_message:
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/* Copy code to new location */
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pushl %edi
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pushw %ax
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xorw %ax, %ax
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movw %ax, %es
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es rep addr32 movsb
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popw %ax
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pushw %bx
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movw $copy_bytes, %bx
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call process_bytes
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popw %bx
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popl %edi
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/* Initialise librm at new location */
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@ -151,7 +151,12 @@ find_mem_bar:
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/* Copy payload to buffer, or set buffer address to BAR address */
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testl %esi, %esi
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jz 1f
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/* We have a buffer; copy payload to it */
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/* We have a buffer; copy payload to it. Since .mrom is
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* designed specifically for real hardware, we assume that
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* flat real mode is working properly. (In the unlikely event
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* that this code is run inside a hypervisor that doesn't
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* properly support flat real mode, it will die horribly.)
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*/
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pushl %esi
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pushw %es
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movl %esi, %edi
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