1 /* SPDX-License-Identifier: GPL-2.0-only */ <<
2 /* 1 /*
3 * thunks.S - assembly helpers for mixed-bitne 2 * thunks.S - assembly helpers for mixed-bitness code
4 * Copyright (c) 2015 Andrew Lutomirski 3 * Copyright (c) 2015 Andrew Lutomirski
5 * 4 *
>> 5 * This program is free software; you can redistribute it and/or modify
>> 6 * it under the terms and conditions of the GNU General Public License,
>> 7 * version 2, as published by the Free Software Foundation.
>> 8 *
>> 9 * This program is distributed in the hope it will be useful, but
>> 10 * WITHOUT ANY WARRANTY; without even the implied warranty of
>> 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
>> 12 * General Public License for more details.
>> 13 *
6 * These are little helpers that make it easie 14 * These are little helpers that make it easier to switch bitness on
7 * the fly. 15 * the fly.
8 */ 16 */
9 17
10 .text 18 .text
11 19
12 .global call32_from_64 20 .global call32_from_64
13 .type call32_from_64, @function 21 .type call32_from_64, @function
14 call32_from_64: 22 call32_from_64:
15 // rdi: stack to use 23 // rdi: stack to use
16 // esi: function to call 24 // esi: function to call
17 25
18 // Save registers 26 // Save registers
19 pushq %rbx 27 pushq %rbx
20 pushq %rbp 28 pushq %rbp
21 pushq %r12 29 pushq %r12
22 pushq %r13 30 pushq %r13
23 pushq %r14 31 pushq %r14
24 pushq %r15 32 pushq %r15
25 pushfq 33 pushfq
26 34
27 // Switch stacks 35 // Switch stacks
28 mov %rsp,(%rdi) 36 mov %rsp,(%rdi)
29 mov %rdi,%rsp 37 mov %rdi,%rsp
30 38
31 // Switch to compatibility mode 39 // Switch to compatibility mode
32 pushq $0x23 /* USER32_CS */ 40 pushq $0x23 /* USER32_CS */
33 pushq $1f 41 pushq $1f
34 lretq 42 lretq
35 43
36 1: 44 1:
37 .code32 45 .code32
38 // Call the function 46 // Call the function
39 call *%esi 47 call *%esi
40 // Switch back to long mode 48 // Switch back to long mode
41 jmp $0x33,$1f 49 jmp $0x33,$1f
42 .code64 50 .code64
43 51
44 1: 52 1:
45 // Restore the stack 53 // Restore the stack
46 mov (%rsp),%rsp 54 mov (%rsp),%rsp
47 55
48 // Restore registers 56 // Restore registers
49 popfq 57 popfq
50 popq %r15 58 popq %r15
51 popq %r14 59 popq %r14
52 popq %r13 60 popq %r13
53 popq %r12 61 popq %r12
54 popq %rbp 62 popq %rbp
55 popq %rbx 63 popq %rbx
56 64
57 ret 65 ret
58 66
59 .size call32_from_64, .-call32_from_64 67 .size call32_from_64, .-call32_from_64
60 <<
61 .section .note.GNU-stack,"",%progbits <<
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