Created
July 29, 2016 13:09
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| diff --git a/kernel/x64/boot.S b/kernel/x64/boot.S | |
| index e541b55..da5798c 100644 | |
| --- a/kernel/x64/boot.S | |
| +++ b/kernel/x64/boot.S | |
| @@ -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 |
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