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 common-user/safe-syscall.S
5 *
6 * Written by Richard Henderson <richard.henderson@linaro.org>
7 * Copyright (C) 2021 Linaro, 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        .text
14        .balign 4
15
16        .register %g2, #scratch
17        .register %g3, #scratch
18
19        .global safe_syscall_base
20        .global safe_syscall_start
21        .global safe_syscall_end
22        .type   safe_syscall_base, @function
23        .type   safe_syscall_start, @function
24        .type   safe_syscall_end, @function
25
26#define STACK_BIAS  2047
27#define PARAM(N)    STACK_BIAS + N*8
28
29        /*
30         * This is the entry point for making a system call. The calling
31         * convention here is that of a C varargs function with the
32         * first argument an 'int *' to the signal_pending flag, the
33         * second one the system call number (as a 'long'), and all further
34         * arguments being syscall arguments (also 'long').
35         */
36safe_syscall_base:
37        .cfi_startproc
38        /*
39         * The syscall calling convention isn't the same as the C one:
40         * we enter with o0 == &signal_pending
41         *               o1 == syscall number
42         *               o2 ... o5, (stack) == syscall arguments
43         *               and return the result in x0
44         * and the syscall instruction needs
45         *               g1 == syscall number
46         *               o0 ... o5 == syscall arguments
47         *               and returns the result in o0
48         * Shuffle everything around appropriately.
49         */
50        mov     %o0, %g2                /* signal_pending pointer */
51        mov     %o1, %g1                /* syscall number */
52        mov     %o2, %o0                /* syscall arguments */
53        mov     %o3, %o1
54        mov     %o4, %o2
55        mov     %o5, %o3
56        ldx     [%sp + PARAM(6)], %o4
57        ldx     [%sp + PARAM(7)], %o5
58
59        /*
60         * This next sequence of code works in conjunction with the
61         * rewind_if_safe_syscall_function(). If a signal is taken
62         * and the interrupted PC is anywhere between 'safe_syscall_start'
63         * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'.
64         * The code sequence must therefore be able to cope with this, and
65         * the syscall instruction must be the final one in the sequence.
66         */
67safe_syscall_start:
68        /* if signal_pending is non-zero, don't do the call */
69        lduw    [%g2], %g3
70        brnz,pn %g3, 2f
71         nop
72        ta      0x6d
73safe_syscall_end:
74        /* code path for having successfully executed the syscall */
75        bcs,pn  %xcc, 1f
76         nop
77        ret
78         nop
79
80        /* code path when we didn't execute the syscall */
812:      set     QEMU_ERESTARTSYS, %o0
82
83        /* code path setting errno */
841:      mov     %o7, %g1
85        call    safe_syscall_set_errno_tail
86         mov    %g1, %o7
87
88        .cfi_endproc
89        .size   safe_syscall_base, .-safe_syscall_base
90