thunks_32.S

 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
17call64_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
291:	.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
381:	.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