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1/* longjmp cleanup function for unwinding past signal handlers.
2 Copyright (C) 1995-2019 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18
19#include <hurd.h>
20#include <thread_state.h>
21#include <hurd/threadvar.h>
22#include <jmpbuf-unwind.h>
23#include <assert.h>
24#include <stdint.h>
25
26
27/* _hurd_setup_sighandler puts a link on the `active resources' chain so that
28 _longjmp_unwind will call this function with the `struct sigcontext *'
29 describing the context interrupted by the signal, when `longjmp' is jumping
30 to an environment that unwinds past the interrupted frame. */
31
32void
33_hurdsig_longjmp_from_handler (void *data, jmp_buf env, int val)
34{
35 struct sigcontext *scp = data;
36 struct hurd_sigstate *ss = _hurd_self_sigstate ();
37 int onstack;
38 inline void cleanup (void)
39 {
40 /* Destroy the MiG reply port used by the signal handler, and restore
41 the reply port in use by the thread when interrupted. */
42 mach_port_t *reply_port = &__hurd_local_reply_port;
43 if (*reply_port)
44 {
45 mach_port_t port = *reply_port;
46 /* Assigning MACH_PORT_DEAD here tells libc's mig_get_reply_port
47 not to get another reply port, but avoids mig_dealloc_reply_port
48 trying to deallocate it after the receive fails (which it will,
49 because the reply port will be bogus, regardless). */
50 *reply_port = MACH_PORT_DEAD;
51 __mach_port_destroy (__mach_task_self (), port);
52 }
53 if (scp->sc_reply_port)
54 __mach_port_destroy (__mach_task_self (), scp->sc_reply_port);
55 }
56
57 __spin_lock (&ss->lock);
58 /* We should only ever be called from _longjmp_unwind (in jmp-unwind.c),
59 which calls us inside a critical section. */
60 assert (__spin_lock_locked (&ss->critical_section_lock));
61 /* Are we on the alternate signal stack now? */
62 onstack = (ss->sigaltstack.ss_flags & SS_ONSTACK);
63 __spin_unlock (&ss->lock);
64
65 if (onstack && ! scp->sc_onstack)
66 {
67 /* We are unwinding off the signal stack. We must use sigreturn to
68 do it robustly. Mutate the sigcontext so that when sigreturn
69 resumes from that context, it will be as if `__longjmp (ENV, VAL)'
70 were done. */
71
72 struct hurd_userlink *link;
73
74 inline uintptr_t demangle_ptr (uintptr_t x)
75 {
76# ifdef PTR_DEMANGLE
77 PTR_DEMANGLE (x);
78# endif
79 return x;
80 }
81
82 /* Continue _longjmp_unwind's job of running the unwind
83 forms for frames being unwound, since we will not
84 return to its loop like this one, which called us. */
85 for (link = ss->active_resources;
86 link && _JMPBUF_UNWINDS (env[0].__jmpbuf, link, demangle_ptr);
87 link = link->thread.next)
88 if (_hurd_userlink_unlink (link))
89 {
90 if (link->cleanup == &_hurdsig_longjmp_from_handler)
91 {
92 /* We are unwinding past another signal handler invocation.
93 Just finish the cleanup for this (inner) one, and then
94 swap SCP to restore to the outer context. */
95 cleanup ();
96 scp = link->cleanup_data;
97 }
98 else
99 (*link->cleanup) (link->cleanup_data, env, val);
100 }
101
102#define sc_machine_thread_state paste(sc_,machine_thread_state)
103#define paste(a,b) paste1(a,b)
104#define paste1(a,b) a##b
105
106 /* There are no more unwind forms to be run!
107 Now we can just have the sigreturn do the longjmp for us. */
108 _hurd_longjmp_thread_state
109 ((struct machine_thread_state *) &scp->sc_machine_thread_state,
110 env, val);
111
112 /* Restore to the same current signal mask. If sigsetjmp saved the
113 mask, longjmp has already restored it as desired; if not, we
114 should leave it as it is. */
115 scp->sc_mask = ss->blocked;
116
117 /* sigreturn expects the link added by _hurd_setup_sighandler
118 to still be there, but _longjmp_unwind removed it just before
119 calling us. Put it back now so sigreturn can find it. */
120 link = (void *) &scp[1];
121 assert (! link->resource.next && ! link->resource.prevp);
122 assert (link->thread.next == ss->active_resources);
123 assert (link->thread.prevp == &ss->active_resources);
124 if (link->thread.next)
125 link->thread.next->thread.prevp = &link->thread.next;
126 ss->active_resources = link;
127
128 /* We must momentarily exit the critical section so that sigreturn
129 does not get upset with us. But we don't want signal handlers
130 running right now, because we are presently in the bogus state of
131 having run all the unwind forms back to ENV's frame, but our SP is
132 still inside those unwound frames. */
133 __spin_lock (&ss->lock);
134 __spin_unlock (&ss->critical_section_lock);
135 ss->blocked = ~(sigset_t) 0 & ~_SIG_CANT_MASK;
136 __spin_unlock (&ss->lock);
137
138 /* Restore to the modified signal context that now
139 performs `longjmp (ENV, VAL)'. */
140 __sigreturn (scp);
141 assert (! "sigreturn returned!");
142 }
143
144 /* We are not unwinding off the alternate signal stack. So nothing
145 really funny is going on here. We can just clean up this handler
146 frame and let _longjmp_unwind continue unwinding. */
147 cleanup ();
148 ss->intr_port = scp->sc_intr_port;
149}
150

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