1 /* SPDX-License-Identifier: GPL-2.0-only */ 1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /* 2 /*
3 * thunks.S - assembly helpers for mixed-bitne 3 * thunks.S - assembly helpers for mixed-bitness code
4 * Copyright (c) 2015 Andrew Lutomirski 4 * Copyright (c) 2015 Andrew Lutomirski
5 * 5 *
6 * These are little helpers that make it easie 6 * These are little helpers that make it easier to switch bitness on
7 * the fly. 7 * the fly.
8 */ 8 */
9 9
10 .text 10 .text
11 11
12 .global call32_from_64 12 .global call32_from_64
13 .type call32_from_64, @function 13 .type call32_from_64, @function
14 call32_from_64: 14 call32_from_64:
15 // rdi: stack to use 15 // rdi: stack to use
16 // esi: function to call 16 // esi: function to call
17 17
18 // Save registers 18 // Save registers
19 pushq %rbx 19 pushq %rbx
20 pushq %rbp 20 pushq %rbp
21 pushq %r12 21 pushq %r12
22 pushq %r13 22 pushq %r13
23 pushq %r14 23 pushq %r14
24 pushq %r15 24 pushq %r15
25 pushfq 25 pushfq
26 26
27 // Switch stacks 27 // Switch stacks
28 mov %rsp,(%rdi) 28 mov %rsp,(%rdi)
29 mov %rdi,%rsp 29 mov %rdi,%rsp
30 30
31 // Switch to compatibility mode 31 // Switch to compatibility mode
32 pushq $0x23 /* USER32_CS */ 32 pushq $0x23 /* USER32_CS */
33 pushq $1f 33 pushq $1f
34 lretq 34 lretq
35 35
36 1: 36 1:
37 .code32 37 .code32
38 // Call the function 38 // Call the function
39 call *%esi 39 call *%esi
40 // Switch back to long mode 40 // Switch back to long mode
41 jmp $0x33,$1f 41 jmp $0x33,$1f
42 .code64 42 .code64
43 43
44 1: 44 1:
45 // Restore the stack 45 // Restore the stack
46 mov (%rsp),%rsp 46 mov (%rsp),%rsp
47 47
48 // Restore registers 48 // Restore registers
49 popfq 49 popfq
50 popq %r15 50 popq %r15
51 popq %r14 51 popq %r14
52 popq %r13 52 popq %r13
53 popq %r12 53 popq %r12
54 popq %rbp 54 popq %rbp
55 popq %rbx 55 popq %rbx
56 56
57 ret 57 ret
58 58
59 .size call32_from_64, .-call32_from_64 59 .size call32_from_64, .-call32_from_64
60 <<
61 .section .note.GNU-stack,"",%progbits <<
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