1/*
2 * safe-syscall.inc.S : host-specific assembly fragment
3 * to handle signals occurring at the same time as system calls.
4 * This is intended to be included by linux-user/safe-syscall.S
5 *
6 * Written by Richard Henderson <rth@twiddle.net>
7 * Copyright (C) 2016 Red Hat, Inc.
8 *
9 * This work is licensed under the terms of the GNU GPL, version 2 or later.
10 * See the COPYING file in the top-level directory.
11 */
12
13	.global safe_syscall_base
14	.global safe_syscall_start
15	.global safe_syscall_end
16	.type	safe_syscall_base, #function
17	.type	safe_syscall_start, #function
18	.type	safe_syscall_end, #function
19
20	/* This is the entry point for making a system call. The calling
21	 * convention here is that of a C varargs function with the
22	 * first argument an 'int *' to the signal_pending flag, the
23	 * second one the system call number (as a 'long'), and all further
24	 * arguments being syscall arguments (also 'long').
25	 * We return a long which is the syscall's return value, which
26	 * may be negative-errno on failure. Conversion to the
27	 * -1-and-errno-set convention is done by the calling wrapper.
28	 */
29safe_syscall_base:
30	.cfi_startproc
31	/* The syscall calling convention isn't the same as the
32	 * C one:
33	 * we enter with x0 == *signal_pending
34	 *               x1 == syscall number
35	 *               x2 ... x7, (stack) == syscall arguments
36	 *               and return the result in x0
37	 * and the syscall instruction needs
38	 *               x8 == syscall number
39	 *               x0 ... x6 == syscall arguments
40	 *               and returns the result in x0
41	 * Shuffle everything around appropriately.
42	 */
43	mov	x9, x0		/* signal_pending pointer */
44	mov	x8, x1		/* syscall number */
45	mov	x0, x2		/* syscall arguments */
46	mov	x1, x3
47	mov	x2, x4
48	mov	x3, x5
49	mov	x4, x6
50	mov	x5, x7
51	ldr	x6, [sp]
52
53	/* This next sequence of code works in conjunction with the
54	 * rewind_if_safe_syscall_function(). If a signal is taken
55	 * and the interrupted PC is anywhere between 'safe_syscall_start'
56	 * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'.
57	 * The code sequence must therefore be able to cope with this, and
58	 * the syscall instruction must be the final one in the sequence.
59	 */
60safe_syscall_start:
61	/* if signal_pending is non-zero, don't do the call */
62	ldr	w10, [x9]
63	cbnz	w10, 0f
64	svc	0x0
65safe_syscall_end:
66	/* code path for having successfully executed the syscall */
67	ret
68
690:
70	/* code path when we didn't execute the syscall */
71	mov	x0, #-TARGET_ERESTARTSYS
72	ret
73	.cfi_endproc
74
75	.size	safe_syscall_base, .-safe_syscall_base
76