1/*
2 * Copyright (C) 2013 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include <private/bionic_asm.h>
30#include <private/bionic_asm_dwarf_exprs.h>
31
32// In the signal trampoline frame, rsp points to a ucontext_t struct.
33
34// Offsets into struct ucontext_t of uc_mcontext.gregs[x].
35#define OFFSET_R8 40
36#define OFFSET_R9 48
37#define OFFSET_R10 56
38#define OFFSET_R11 64
39#define OFFSET_R12 72
40#define OFFSET_R13 80
41#define OFFSET_R14 88
42#define OFFSET_R15 96
43#define OFFSET_RDI 104
44#define OFFSET_RSI 112
45#define OFFSET_RBP 120
46#define OFFSET_RBX 128
47#define OFFSET_RDX 136
48#define OFFSET_RAX 144
49#define OFFSET_RCX 152
50#define OFFSET_RSP 160
51#define OFFSET_RIP 168
52
53// Non-standard DWARF constants for the x86-64 registers.
54#define DW_x86_64_RAX 0
55#define DW_x86_64_RDX 1
56#define DW_x86_64_RCX 2
57#define DW_x86_64_RBX 3
58#define DW_x86_64_RSI 4
59#define DW_x86_64_RDI 5
60#define DW_x86_64_RBP 6
61#define DW_x86_64_RSP 7
62#define DW_x86_64_R8 8
63#define DW_x86_64_R9 9
64#define DW_x86_64_R10 10
65#define DW_x86_64_R11 11
66#define DW_x86_64_R12 12
67#define DW_x86_64_R13 13
68#define DW_x86_64_R14 14
69#define DW_x86_64_R15 15
70#define DW_x86_64_RIP 16
71
72// Insert a nop between .cfi_startproc and the trampoline symbol so that unwinders can find the FDE.
73// A function's last instruction can be a call instruction (e.g. to __cxa_throw), in which case the
74// return address (e.g. from __cxa_throw to the caller) will be just after the function. This
75// address may also be the start of the next function, so to avoid ambiguity, unwinders assume that
76// a return address PC can refer to the address just after a function, but never to the start of a
77// function. (This is implemented by subtracting 1 from the return address PC before looking it up.)
78// This is fine for ordinary functions, but breaks on trampolines. Inserting a nop fixes it.
79//
80// N.B. Unwinders have two other strategies for recognizing the signal trampoline:
81//  - Read the instructions that the return address PC points at and look for a sigreturn syscall.
82//    (Hence, the instructions must not change at all.)
83//  - Do a symbol table lookup and check that against the PC (e.g. LLDB looks for
84//    __kernel_rt_sigreturn and __restore_rt.)
85// Either way, the nop is needed to avoid ambiguity if the function before the trampoline could end
86// with a call.
87
88#define RESTORE_GPR(reg) m_cfi_breg_offset DW_x86_64_ ## reg, DW_x86_64_RSP, OFFSET_ ## reg;
89
90  .text
91  .cfi_startproc
92  .cfi_signal_frame
93  m_cfi_def_cfa_deref DW_x86_64_RSP, OFFSET_RSP
94  RESTORE_GPR(R8)
95  RESTORE_GPR(R9)
96  RESTORE_GPR(R10)
97  RESTORE_GPR(R11)
98  RESTORE_GPR(R12)
99  RESTORE_GPR(R13)
100  RESTORE_GPR(R14)
101  RESTORE_GPR(R15)
102  RESTORE_GPR(RDI)
103  RESTORE_GPR(RSI)
104  RESTORE_GPR(RBP)
105  RESTORE_GPR(RBX)
106  RESTORE_GPR(RDX)
107  RESTORE_GPR(RAX)
108  RESTORE_GPR(RCX)
109  // Restoring RSP is unnecessary as the unwinder simply uses the CFA value.
110  RESTORE_GPR(RIP)
111  nop
112ENTRY_NO_DWARF_PRIVATE(__restore_rt)
113  mov $__NR_rt_sigreturn, %rax
114  syscall
115END(__restore_rt)
116