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#include "sys/regdef.h"
14#include "sys/asm.h"
15
16        .text
17        .set    nomips16
18        .set    reorder
19
20        .global safe_syscall_start
21        .global safe_syscall_end
22        .type   safe_syscall_start, @function
23        .type   safe_syscall_end, @function
24
25        /*
26         * This is the entry point for making a system call. The calling
27         * convention here is that of a C varargs function with the
28         * first argument an 'int *' to the signal_pending flag, the
29         * second one the system call number (as a 'long'), and all further
30         * arguments being syscall arguments (also 'long').
31         */
32
33#if _MIPS_SIM == _ABIO32
34/* 8 * 4 = 32 for outgoing parameters; 1 * 4 for s0 save; 1 * 4 for align. */
35#define FRAME    40
36#define OFS_S0   32
37#else
38/* 1 * 8 for s0 save; 1 * 8 for align. */
39#define FRAME    16
40#define OFS_S0   0
41#endif
42
43
44NESTED(safe_syscall_base, FRAME, ra)
45        .cfi_startproc
46        PTR_ADDIU sp, sp, -FRAME
47        .cfi_adjust_cfa_offset FRAME
48        REG_S   s0, OFS_S0(sp)
49        .cfi_rel_offset s0, OFS_S0
50#if _MIPS_SIM == _ABIO32
51        /*
52         * The syscall calling convention is nearly the same as C:
53         * we enter with a0 == &signal_pending
54         *               a1 == syscall number
55         *               a2, a3, stack == syscall arguments
56         *               and return the result in a0
57         * and the syscall instruction needs
58         *               v0 == syscall number
59         *               a0 ... a3, stack == syscall arguments
60         *               and returns the result in v0
61         * Shuffle everything around appropriately.
62         */
63        move    s0, a0          /* signal_pending pointer */
64        move    v0, a1          /* syscall number */
65        move    a0, a2          /* syscall arguments */
66        move    a1, a3
67        lw      a2, FRAME+16(sp)
68        lw      a3, FRAME+20(sp)
69        lw      t4, FRAME+24(sp)
70        lw      t5, FRAME+28(sp)
71        lw      t6, FRAME+32(sp)
72        lw      t7, FRAME+40(sp)
73        sw      t4, 16(sp)
74        sw      t5, 20(sp)
75        sw      t6, 24(sp)
76        sw      t7, 28(sp)
77#else
78        /*
79         * The syscall calling convention is nearly the same as C:
80         * we enter with a0 == &signal_pending
81         *               a1 == syscall number
82         *               a2 ... a7 == syscall arguments
83         *               and return the result in a0
84         * and the syscall instruction needs
85         *               v0 == syscall number
86         *               a0 ... a5 == syscall arguments
87         *               and returns the result in v0
88         * Shuffle everything around appropriately.
89         */
90        move    s0, a0          /* signal_pending pointer */
91        move    v0, a1          /* syscall number */
92        move    a0, a2          /* syscall arguments */
93        move    a1, a3
94        move    a2, a4
95        move    a3, a5
96        move    a4, a6
97        move    a5, a7
98#endif
99
100        /*
101         * This next sequence of code works in conjunction with the
102         * rewind_if_safe_syscall_function(). If a signal is taken
103         * and the interrupted PC is anywhere between 'safe_syscall_start'
104         * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'.
105         * The code sequence must therefore be able to cope with this, and
106         * the syscall instruction must be the final one in the sequence.
107         */
108safe_syscall_start:
109        /* If signal_pending is non-zero, don't do the call */
110        lw      t1, 0(s0)
111        bnez    t1, 2f
112        syscall
113safe_syscall_end:
114
115        /* code path for having successfully executed the syscall */
116        REG_L   s0, OFS_S0(sp)
117        PTR_ADDIU sp, sp, FRAME
118        .cfi_remember_state
119        .cfi_adjust_cfa_offset -FRAME
120        .cfi_restore s0
121        bnez    a3, 1f
122        jr      ra
123        .cfi_restore_state
124
125        /* code path when we didn't execute the syscall */
1262:      REG_L   s0, OFS_S0(sp)
127        PTR_ADDIU sp, sp, FRAME
128        .cfi_adjust_cfa_offset -FRAME
129        .cfi_restore s0
130        li      v0, QEMU_ERESTARTSYS
131
132        /* code path setting errno */
133        /*
134         * We didn't setup GP on entry, optimistic of the syscall success.
135         * We must do so now to load the address of the helper, as required
136         * by the ABI, into t9.
137         *
138         * Note that SETUP_GPX and SETUP_GPX64 are themselves conditional,
139         * so we can simply let the one that's not empty succeed.
140         */
1411:      USE_ALT_CP(t0)
142        SETUP_GPX(t1)
143        SETUP_GPX64(t0, t1)
144        move    a0, v0
145        PTR_LA  t9, safe_syscall_set_errno_tail
146        jr      t9
147
148        .cfi_endproc
149END(safe_syscall_base)
150