1/* Copyright (C) 1999-2022 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library. If not, see
16 <https://www.gnu.org/licenses/>. */
17
18#include <sysdep.h>
19
20/* If no SA_RESTORER function was specified by the application we use
21 one of these. This avoids the need for the kernel to synthesise a return
22 instruction on the stack, which would involve expensive cache flushes.
23
24 Nowadays (2.6 series, and somewhat earlier) the kernel uses a high page
25 for signal trampolines, so the cache flushes are not an issue. But since
26 we do not have a vDSO, continue to use these so that we can provide
27 unwind information.
28
29 Start the unwind tables at least one instruction before the signal
30 trampoline, because the unwinder will assume we are returning after
31 a call site. */
32
33/* Used in ENTRY. */
34#undef cfi_startproc
35#define cfi_startproc \
36 .cfi_startproc simple; \
37 .cfi_signal_frame
38
39/* The CFA is not computed / used correctly here; this is neither trivial to
40 do, nor is it needed. */
41#define CFI \
42 cfi_def_cfa (sp, 0); \
43 cfi_offset (r0, OFFSET + 0 * 4); \
44 cfi_offset (r1, OFFSET + 1 * 4); \
45 cfi_offset (r2, OFFSET + 2 * 4); \
46 cfi_offset (r3, OFFSET + 3 * 4); \
47 cfi_offset (r4, OFFSET + 4 * 4); \
48 cfi_offset (r5, OFFSET + 5 * 4); \
49 cfi_offset (r6, OFFSET + 6 * 4); \
50 cfi_offset (r7, OFFSET + 7 * 4); \
51 cfi_offset (r8, OFFSET + 8 * 4); \
52 cfi_offset (r9, OFFSET + 9 * 4); \
53 cfi_offset (r10, OFFSET + 10 * 4); \
54 cfi_offset (r11, OFFSET + 11 * 4); \
55 cfi_offset (r12, OFFSET + 12 * 4); \
56 cfi_offset (r13, OFFSET + 13 * 4); \
57 cfi_offset (r14, OFFSET + 14 * 4); \
58 cfi_offset (r15, OFFSET + 15 * 4)
59
60#define OFFSET 32
61 .fnstart
62 .save {r0-r15}
63 .pad #OFFSET
64 nop
65ENTRY(__default_sa_restorer)
66 CFI
67 mov r7, $SYS_ify(sigreturn)
68 swi 0x0
69 .fnend
70END(__default_sa_restorer)
71#undef OFFSET
72
73#define OFFSET 160
74 .fnstart
75 .save {r0-r15}
76 .pad #OFFSET
77 nop
78ENTRY(__default_rt_sa_restorer)
79 CFI
80 mov r7, $SYS_ify(rt_sigreturn)
81 swi 0x0
82 .fnend
83END(__default_rt_sa_restorer)
84#undef OFFSET
85

source code of glibc/sysdeps/unix/sysv/linux/arm/sigrestorer.S