1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3  * thunks_32.S - assembly helpers for mixed-bitness code
4  * Copyright (c) 2015 Denys Vlasenko
5  *
6  * These are little helpers that make it easier to switch bitness on
7  * the fly.
8  */
9 
10 	.text
11 	.code32
12 
13 	.global call64_from_32
14 	.type call32_from_64, @function
15 
16 	// 4(%esp): function to call
17 call64_from_32:
18 	// Fetch function address
19 	mov	4(%esp), %eax
20 
21 	// Save registers which are callee-clobbered by 64-bit ABI
22 	push	%ecx
23 	push	%edx
24 	push	%esi
25 	push	%edi
26 
27 	// Switch to long mode
28 	jmp	$0x33,$1f
29 1:	.code64
30 
31 	// Call the function
32 	call	*%rax
33 
34 	// Switch to compatibility mode
35 	push	$0x23  /* USER32_CS */
36 	.code32; push $1f; .code64 /* hack: can't have X86_64_32S relocation in 32-bit ELF */
37 	lretq
38 1:	.code32
39 
40 	pop	%edi
41 	pop	%esi
42 	pop	%edx
43 	pop	%ecx
44 
45 	ret
46 
47 .size call64_from_32, .-call64_from_32
48 
49 .section .note.GNU-stack,"",%progbits
50