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Fix undefined stack register after switch into long mode.

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Thanks to dminuoso for pointing out the issue.
This commit is contained in:
Jonas 'Sortie' Termansen 2016-07-29 15:16:11 +02:00
parent 2141c95621
commit 8f81f990f8
1 changed files with 9 additions and 0 deletions
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9
kernel/x64/boot.S
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@ -174,6 +174,15 @@ __start:
.code64
2:
# The upper 32 bits of the general purpose registers are *undefined* after
# switching into 64-bit mode (Intel Manual, Vol 1, 3.4.1.1 "General-Purpose
# Registers in 64-Bit Mode"). The lower 32 bits are preserved from 32-bit
# mode. Any registers whose value we wish to retain must have its upper 32
# bits masked off. Assigning a register to itself in a 32-bit operation will
# zero the upper 32 bits. The only register the below code assumes is
# retained is the stack register (esp/rsp).
mov %esp, %esp
# Switch ds, es, fs, gs, ss to the kernel data segment (0x10).
movw $0x10, %cx
movw %cx, %ds