1/* AArch64 support code for fibers and multithreading.
2   Copyright (C) 2019-2020 Free Software Foundation, Inc.
3
4This file is part of GCC.
5
6GCC is free software; you can redistribute it and/or modify it under
7the terms of the GNU General Public License as published by the Free
8Software Foundation; either version 3, or (at your option) any later
9version.
10
11GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12WARRANTY; without even the implied warranty of MERCHANTABILITY or
13FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14for more details.
15
16Under Section 7 of GPL version 3, you are granted additional
17permissions described in the GCC Runtime Library Exception, version
183.1, as published by the Free Software Foundation.
19
20You should have received a copy of the GNU General Public License and
21a copy of the GCC Runtime Library Exception along with this program;
22see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
23<http://www.gnu.org/licenses/>.  */
24
25#include "../common/threadasm.S"
26
27/**
28 * preserve/restore AAPCS64 registers
29 *   x19-x28 5.1.1 64-bit callee saved
30 *   x29 fp, or possibly callee saved reg - depends on platform choice 5.2.3)
31 *   x30 lr
32 *   d8-d15  5.1.2 says callee only must save bottom 64-bits (the "d" regs)
33 *
34 * saved regs on stack will look like:
35 *   19: x19
36 *   18: x20
37 *   ...
38 *   10: x28
39 *    9: x29 (fp)  <-- oldp / *newp save stack top
40 *    8: x30 (lr)
41 *    7: d8
42 *   ...
43 *    0: d15       <-- sp
44 */
45    .text
46    .global CSYM(fiber_switchContext)
47    .type CSYM(fiber_switchContext), %function
48    .align 4
49CSYM(fiber_switchContext):
50    .cfi_startproc
51    stp     d15, d14, [sp, #-20*8]!
52    stp     d13, d12, [sp, #2*8]
53    stp     d11, d10, [sp, #4*8]
54    stp     d9, d8,   [sp, #6*8]
55    stp     x30, x29, [sp, #8*8] // lr, fp
56    stp     x28, x27, [sp, #10*8]
57    stp     x26, x25, [sp, #12*8]
58    stp     x24, x23, [sp, #14*8]
59    stp     x22, x21, [sp, #16*8]
60    stp     x20, x19, [sp, #18*8]
61
62    // oldp is set above saved lr (x30) to hide it and float regs
63    // from GC
64    add     x19, sp, #9*8
65    str     x19, [x0]       // *oldp tstack
66    sub     sp, x1, #9*8    // switch to newp sp
67
68    ldp     x20, x19, [sp, #18*8]
69    ldp     x22, x21, [sp, #16*8]
70    ldp     x24, x23, [sp, #14*8]
71    ldp     x26, x25, [sp, #12*8]
72    ldp     x28, x27, [sp, #10*8]
73    ldp     x30, x29, [sp, #8*8] // lr, fp
74    ldp     d9, d8,   [sp, #6*8]
75    ldp     d11, d10, [sp, #4*8]
76    ldp     d13, d12, [sp, #2*8]
77    ldp     d15, d14, [sp], #20*8
78    ret
79    .cfi_endproc
80    .size CSYM(fiber_switchContext),.-CSYM(fiber_switchContext)
81
82/**
83 * When generating any kind of backtrace (gdb, exception handling) for
84 * a function called in a Fiber, we need to tell the unwinder to stop
85 * at our Fiber main entry point, i.e. we need to mark the bottom of
86 * the call stack. This can be done by clearing the link register lr
87 * prior to calling fiber_entryPoint (i.e. in fiber_switchContext) or
88 * using a .cfi_undefined directive for the link register in the
89 * Fiber entry point. cfi_undefined seems to yield better results in gdb.
90 * Unfortunately we can't place it into fiber_entryPoint using inline
91 * asm, so we use this trampoline instead.
92 */
93    .text
94    .global CSYM(fiber_trampoline)
95    .p2align  2
96    .type CSYM(fiber_trampoline), %function
97CSYM(fiber_trampoline):
98    .cfi_startproc
99    .cfi_undefined x30
100    // fiber_entryPoint never returns
101    bl CSYM(fiber_entryPoint)
102    .cfi_endproc
103    .size CSYM(fiber_trampoline),.-CSYM(fiber_trampoline)
104