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x86 setup: make PM transition more paranoid; cleanup 32-bit entry

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Make the transition to protected mode more paranoid by having
back-to-back near jump (to synchronize the 386/486 prefetch queue) and
far jump (to set up the code segment.)

While we're at it, zero as many registers as practical (for future
expandability of the 32-bit entry interface) and enter 32-bit mode
with a valid stack.  Note that the 32-bit code cannot rely on this
stack, or we'll break all other existing users of the 32-bit
entrypoint, but it may make debugging hacks easier to write.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
H. Peter Anvin 2008-01-30 13:33:01 +01:00 committed by Ingo Molnar
parent 2a6648e65a
commit c4d9ba6da9
1 changed files with 32 additions and 12 deletions
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44
arch/x86/boot/pmjump.S
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@ -29,12 +29,13 @@
*/
protected_mode_jump:
movl %edx, %esi # Pointer to boot_params table
movl %eax, 2f # Patch ljmpl instruction
xorl %ebx, %ebx
movw %cs, %bx
shll $4, %ebx
addl %ebx, 2f
movw $__BOOT_DS, %cx
xorl %ebx, %ebx # Per the 32-bit boot protocol
xorl %ebp, %ebp # Per the 32-bit boot protocol
xorl %edi, %edi # Per the 32-bit boot protocol
movl %cr0, %edx
orb $1, %dl # Protected mode (PE) bit
@ -42,15 +43,34 @@ protected_mode_jump:
jmp 1f # Short jump to serialize on 386/486
1:
movw %cx, %ds
movw %cx, %es
movw %cx, %fs
movw %cx, %gs
movw %cx, %ss
# Jump to the 32-bit entrypoint
# Transition to 32-bit mode
.byte 0x66, 0xea # ljmpl opcode
2: .long 0 # offset
2: .long in_pm32 # offset
.word __BOOT_CS # segment
.size protected_mode_jump, .-protected_mode_jump
.code32
.type in_pm32, @function
in_pm32:
# Set up data segments for flat 32-bit mode
movl %ecx, %ds
movl %ecx, %es
movl %ecx, %fs
movl %ecx, %gs
movl %ecx, %ss
# The 32-bit code sets up its own stack, but this way we do have
# a valid stack if some debugging hack wants to use it.
addl %ebx, %esp
# Clear registers to allow for future extensions to the
# 32-bit boot protocol
xorl %ecx, %ecx
xorl %edx, %edx
xorl %ebx, %ebx
xorl %ebp, %ebp
xorl %edi, %edi
jmpl *%eax # Jump to the 32-bit entrypoint
.size in_pm32, .-in_pm32