1/* Copyright (C) 1991-2024 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 <hurd.h>
19#include <hurd/signal.h>
20#include <hurd/msg.h>
21#include <stdlib.h>
22
23/* This is run on the thread stack after restoring it, to be able to
24 unlock SS off sigstack. */
25void
26__sigreturn2 (struct hurd_sigstate *ss, uintptr_t *usp,
27 mach_port_t sc_reply_port)
28{
29 mach_port_t reply_port;
30 _hurd_sigstate_unlock (ss);
31
32 /* Destroy the MiG reply port used by the signal handler, and restore the
33 reply port in use by the thread when interrupted.
34
35 We cannot use the original reply port for our RPCs that we do here, since
36 we could unexpectedly receive/consume a reply message meant for the user
37 (in particular, msg_sig_post_reply), and also since we would deallocate
38 the port if *our* RPC fails, which we don't want to do since the user
39 still has the old name. And so, temporarily set MACH_PORT_DEAD as our
40 reply name, and make sure destroying the port is the very last RPC we
41 do. */
42 reply_port = THREAD_GETMEM (THREAD_SELF, reply_port);
43 THREAD_SETMEM (THREAD_SELF, reply_port, MACH_PORT_DEAD);
44 if (__glibc_likely (MACH_PORT_VALID (reply_port)))
45 (void) __mach_port_mod_refs (__mach_task_self (), reply_port,
46 MACH_PORT_RIGHT_RECEIVE, -1);
47 THREAD_SETMEM (THREAD_SELF, reply_port, sc_reply_port);
48
49 asm volatile (
50 /* Point the stack to the register dump. */
51 "movq %0, %%rsp\n"
52 /* Pop off the registers. */
53 "popq %%r8\n"
54 "popq %%r9\n"
55 "popq %%r10\n"
56 "popq %%r11\n"
57 "popq %%r12\n"
58 "popq %%r13\n"
59 "popq %%r14\n"
60 "popq %%r15\n"
61 "popq %%rdi\n"
62 "popq %%rsi\n"
63 "popq %%rbp\n"
64 "popq %%rbx\n"
65 "popq %%rdx\n"
66 "popq %%rcx\n"
67 "popq %%rax\n"
68 "popfq\n"
69 /* Restore %rip and %rsp with a single instruction. */
70 "retq $128" :
71 : "rm" (usp));
72 __builtin_unreachable ();
73}
74
75int
76__sigreturn (struct sigcontext *scp)
77{
78 struct hurd_sigstate *ss;
79 struct hurd_userlink *link = (void *) &scp[1];
80 uintptr_t *usp;
81 mach_port_t sc_reply_port;
82
83 if (__glibc_unlikely (scp == NULL || (scp->sc_mask & _SIG_CANT_MASK)))
84 return __hurd_fail (EINVAL);
85
86 ss = _hurd_self_sigstate ();
87 _hurd_sigstate_lock (ss);
88
89 /* Remove the link on the `active resources' chain added by
90 _hurd_setup_sighandler. Its purpose was to make sure
91 that we got called; now we have, it is done. */
92 _hurd_userlink_unlink (link);
93
94 /* Restore the set of blocked signals, and the intr_port slot. */
95 ss->blocked = scp->sc_mask;
96 ss->intr_port = scp->sc_intr_port;
97
98 /* Check for pending signals that were blocked by the old set. */
99 if (_hurd_sigstate_pending (ss) & ~ss->blocked)
100 {
101 /* There are pending signals that just became unblocked. Wake up the
102 signal thread to deliver them. But first, squirrel away SCP where
103 the signal thread will notice it if it runs another handler, and
104 arrange to have us called over again in the new reality. */
105 ss->context = scp;
106 _hurd_sigstate_unlock (ss);
107 __msg_sig_post (_hurd_msgport, 0, 0, __mach_task_self ());
108 /* If a pending signal was handled, sig_post never returned.
109 If it did return, the pending signal didn't run a handler;
110 proceed as usual. */
111 _hurd_sigstate_lock (ss);
112 ss->context = NULL;
113 }
114
115 if (scp->sc_onstack)
116 ss->sigaltstack.ss_flags &= ~SS_ONSTACK;
117
118 if (scp->sc_fpused)
119 /* Restore the FPU state. Mach conveniently stores the state
120 in the format the i387 `frstor' instruction uses to restore it. */
121 asm volatile ("frstor %0" : : "m" (scp->sc_fpsave));
122
123 /* Copy the registers onto the user's stack, to be able to release the
124 altstack (by unlocking sigstate). Note that unless an altstack is used,
125 the sigcontext will itself be located on the user's stack, so we may well
126 be overwriting it here (or later in __sigreturn2).
127
128 So: do this very carefully. First, load sc_reply_port, which is the only
129 other bit of sigcontext that __sigreturn2 needs. Then copy the registers
130 without reordering them, but skipping the ones we won't need. We have to
131 copy starting from the larger addresses down, since our register dump is
132 located at a larger address than the sigcontext. */
133
134 sc_reply_port = scp->sc_reply_port;
135 usp = (uintptr_t *) (scp->sc_ursp - 128);
136
137 *--usp = scp->sc_rip;
138 *--usp = scp->sc_rfl;
139 *--usp = scp->sc_rax;
140 *--usp = scp->sc_rcx;
141 *--usp = scp->sc_rdx;
142 *--usp = scp->sc_rbx;
143 *--usp = scp->sc_rbp;
144 *--usp = scp->sc_rsi;
145 *--usp = scp->sc_rdi;
146 *--usp = scp->sc_r15;
147 *--usp = scp->sc_r14;
148 *--usp = scp->sc_r13;
149 *--usp = scp->sc_r12;
150 *--usp = scp->sc_r11;
151 *--usp = scp->sc_r10;
152 *--usp = scp->sc_r9;
153 *--usp = scp->sc_r8;
154
155 /* Switch to the user's stack that we have just prepared, and call
156 __sigreturn2. Clobber "memory" to make sure GCC flushes the stack
157 setup to actual memory. We align the stack as per the ABI, but pass
158 the original usp to __sigreturn2 as an argument. */
159 asm volatile ("movq %1, %%rsp\n"
160 "andq $-16, %%rsp\n"
161 "call __sigreturn2" :
162 : "D" (ss), "S" (usp), "d" (sc_reply_port)
163 : "memory");
164 __builtin_unreachable ();
165}
166
167weak_alias (__sigreturn, sigreturn)
168

source code of glibc/sysdeps/mach/hurd/x86_64/sigreturn.c