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[Xen-devel] A useless short jmp?
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| Subject: | [Xen-devel] A useless short jmp? |
| From: | "Li, Xin B" <xin.b.li@xxxxxxxxx> |
| Date: | Mon, 18 Jun 2007 22:03:19 +0800 |
| Delivery-date: | Mon, 18 Jun 2007 07:01:30 -0700 |
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| Thread-topic: | A useless short jmp? |
In trampoline.S we have a short jmp after lmsw:
trampoline_realmode_entry:
mov %cs,%ax
mov %ax,%ds
movb $0xA5,bootsym(trampoline_cpu_started)
cld
cli
lidt bootsym(idt_48)
lgdt bootsym(gdt_48)
xor %ax, %ax
inc %ax
lmsw %ax # CR0.PE = 1 (enter protected
mode)
mov $1,%bl # EBX != 0 indicates we are an
AP
jmp 1f
1: ljmpl $BOOT_CS32,$bootsym_phys(trampoline_protmode_entry)
According to Intel Spec, it's useless, do we have any special reason to
have it there?
BTW why put mov $1, %bl between lmsw and it's corresponding ljmp?
thanks
-Xin
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