Linux kernel mirror (for testing)
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linux
1/*
2 * thunks_32.S - assembly helpers for mixed-bitness code
3 * Copyright (c) 2015 Denys Vlasenko
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 *
14 * These are little helpers that make it easier to switch bitness on
15 * the fly.
16 */
17
18 .text
19 .code32
20
21 .global call64_from_32
22 .type call32_from_64, @function
23
24 // 4(%esp): function to call
25call64_from_32:
26 // Fetch function address
27 mov 4(%esp), %eax
28
29 // Save registers which are callee-clobbered by 64-bit ABI
30 push %ecx
31 push %edx
32 push %esi
33 push %edi
34
35 // Switch to long mode
36 jmp $0x33,$1f
371: .code64
38
39 // Call the function
40 call *%rax
41
42 // Switch to compatibility mode
43 push $0x23 /* USER32_CS */
44 .code32; push $1f; .code64 /* hack: can't have X86_64_32S relocation in 32-bit ELF */
45 lretq
461: .code32
47
48 pop %edi
49 pop %esi
50 pop %edx
51 pop %ecx
52
53 ret
54
55.size call64_from_32, .-call64_from_32