| /* SPDX-License-Identifier: GPL-2.0-only */ |
| |
| .code32 |
| |
| .section .init, "ax", @progbits |
| |
| .section .init._gdt_, "ax", @progbits |
| |
| .globl gdt_init |
| gdt_init: |
| lgdt %cs:gdtptr |
| ret |
| |
| .previous |
| .align 4 |
| .globl gdtptr |
| gdtptr: |
| .word gdt_end - gdt -1 /* compute the table limit */ |
| .long gdt /* we know the offset */ |
| |
| #ifdef __x86_64__ |
| .code64 |
| .section .init._gdt64_, "ax", @progbits |
| .globl gdt_init64 |
| gdt_init64: |
| /* Workaround a bug in the assembler. |
| * The following code doesn't work: |
| * lgdt gdtptr64 |
| * |
| * The assembler tries to save memory by using 32bit displacement addressing mode. |
| * Displacements are using signed integers. |
| * This is fine in protected mode, as the negative address points to the correct |
| * address > 2GiB, but in long mode this doesn't work at all. |
| * Tests showed that QEMU can gracefully handle it, but real CPUs can't. |
| * |
| * Use the movabs pseudo instruction to force using a 64bit absolute address. |
| */ |
| movabs $gdtptr64, %rax |
| lgdt (%rax) |
| ret |
| |
| .previous |
| .align 4 |
| .globl gdtptr64 |
| gdtptr64: |
| .word gdt_end - gdt -1 /* compute the table limit */ |
| .quad gdt /* we know the offset */ |
| #endif |
| |
| .align 4 |
| gdt: |
| /* selgdt 0, unused */ |
| .word 0x0000, 0x0000 /* dummy */ |
| .byte 0x00, 0x00, 0x00, 0x00 |
| |
| /* selgdt 0x08, flat code segment */ |
| .word 0xffff, 0x0000 |
| .byte 0x00, 0x9b, 0xcf, 0x00 /* G=1 and 0x0f, So we get 4Gbytes |
| for limit */ |
| |
| /* selgdt 0x10,flat data segment */ |
| .word 0xffff, 0x0000 |
| .byte 0x00, 0x93, 0xcf, 0x00 |
| |
| /* selgdt 0x18, flat code segment (64-bit) */ |
| .word 0xffff, 0x0000 |
| .byte 0x00, 0x9b, 0xaf, 0x00 |
| |
| gdt_end: |
