| Patrick Georgi | 11f0079 | 2020-03-04 15:10:45 +0100 | [diff] [blame] | 1 | /* SPDX-License-Identifier: GPL-2.0-only */ |
| Patrick Georgi | 11f0079 | 2020-03-04 15:10:45 +0100 | [diff] [blame] | 2 | |
| Hannah Williams | d3c0c0c | 2018-04-27 09:09:04 -0700 | [diff] [blame] | 3 | .code32 |
| 4 | .section ".text._gdt_", "ax", @progbits |
| 5 | |
| 6 | .globl gdt_init |
| 7 | gdt_init: |
| 8 | lgdt %cs:gdtptr |
| 9 | ret |
| 10 | |
| 11 | .previous |
| 12 | .align 4 |
| 13 | .globl gdtptr |
| Hannah Williams | d3c0c0c | 2018-04-27 09:09:04 -0700 | [diff] [blame] | 14 | gdtptr: |
| 15 | .word gdt_end - gdt -1 /* compute the table limit */ |
| 16 | .long gdt /* we know the offset */ |
| Patrick Rudolph | 4e8dee5 | 2019-03-03 17:58:54 +0100 | [diff] [blame] | 17 | |
| Patrick Rudolph | 8daa12f | 2018-12-26 15:12:32 +0100 | [diff] [blame] | 18 | #ifdef __x86_64__ |
| 19 | .code64 |
| 20 | .section ".text._gdt64_", "ax", @progbits |
| 21 | .globl gdt_init64 |
| 22 | gdt_init64: |
| Patrick Rudolph | 29ed4f5 | 2020-07-05 08:46:55 +0200 | [diff] [blame] | 23 | /* Workaround a bug in the assembler. |
| 24 | * The following code doesn't work: |
| 25 | * lgdt gdtptr64 |
| 26 | * |
| 27 | * The assembler tries to save memory by using 32bit displacement addressing mode. |
| 28 | * Displacements are using signed integers. |
| 29 | * This is fine in protected mode, as the negative address points to the correct |
| 30 | * address > 2GiB, but in long mode this doesn't work at all. |
| 31 | * Tests showed that QEMU can gracefully handle it, but real CPUs can't. |
| 32 | * |
| 33 | * Use the movabs pseudo instruction to force using a 64bit absolute address. |
| 34 | */ |
| 35 | movabs $gdtptr64, %rax |
| 36 | lgdt (%rax) |
| Patrick Rudolph | 8daa12f | 2018-12-26 15:12:32 +0100 | [diff] [blame] | 37 | ret |
| 38 | |
| 39 | .previous |
| 40 | .align 4 |
| 41 | .globl gdtptr64 |
| 42 | gdtptr64: |
| 43 | .word gdt_end - gdt -1 /* compute the table limit */ |
| 44 | .quad gdt /* we know the offset */ |
| 45 | #endif |
| 46 | |
| Patrick Rudolph | 4e8dee5 | 2019-03-03 17:58:54 +0100 | [diff] [blame] | 47 | .align 4 |
| 48 | gdt: |
| 49 | /* selgdt 0, unused */ |
| 50 | .word 0x0000, 0x0000 /* dummy */ |
| 51 | .byte 0x00, 0x00, 0x00, 0x00 |
| Hannah Williams | d3c0c0c | 2018-04-27 09:09:04 -0700 | [diff] [blame] | 52 | |
| 53 | /* selgdt 0x08, flat code segment */ |
| 54 | .word 0xffff, 0x0000 |
| 55 | .byte 0x00, 0x9b, 0xcf, 0x00 /* G=1 and 0x0f, So we get 4Gbytes |
| 56 | for limit */ |
| 57 | |
| 58 | /* selgdt 0x10,flat data segment */ |
| 59 | .word 0xffff, 0x0000 |
| 60 | .byte 0x00, 0x93, 0xcf, 0x00 |
| 61 | |
| 62 | /* selgdt 0x18, flat code segment (64-bit) */ |
| 63 | .word 0xffff, 0x0000 |
| 64 | .byte 0x00, 0x9b, 0xaf, 0x00 |
| 65 | |
| 66 | gdt_end: |