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/* SPDX-License-Identifier: GPL-2.0-only */
.code32
.section ".text._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 ".text._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:
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