aboutsummaryrefslogtreecommitdiff
path: root/arch/um/os-Linux/signal.c
blob: 91a35da5fe90dadb65aa6b0f499d720c7094e21b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
/*
 * Copyright (C) 2004 PathScale, Inc
 * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <stdlib.h>
#include <stdarg.h>
#include <errno.h>
#include <signal.h>
#include <strings.h>
#include "as-layout.h"
#include "kern_util.h"
#include "os.h"
#include "sysdep/barrier.h"
#include "sysdep/sigcontext.h"
#include "user.h"

/* Copied from linux/compiler-gcc.h since we can't include it directly */
#define barrier() __asm__ __volatile__("": : :"memory")

void (*sig_info[NSIG])(int, struct uml_pt_regs *) = {
	[SIGTRAP]	= relay_signal,
	[SIGFPE]	= relay_signal,
	[SIGILL]	= relay_signal,
	[SIGWINCH]	= winch,
	[SIGBUS]	= bus_handler,
	[SIGSEGV]	= segv_handler,
	[SIGIO]		= sigio_handler,
	[SIGVTALRM]	= timer_handler };

static void sig_handler_common(int sig, struct sigcontext *sc)
{
	struct uml_pt_regs r;
	int save_errno = errno;

	r.is_user = 0;
	if (sig == SIGSEGV) {
		/* For segfaults, we want the data from the sigcontext. */
		copy_sc(&r, sc);
		GET_FAULTINFO_FROM_SC(r.faultinfo, sc);
	}

	/* enable signals if sig isn't IRQ signal */
	if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGVTALRM))
		unblock_signals();

	(*sig_info[sig])(sig, &r);

	errno = save_errno;
}

/*
 * These are the asynchronous signals.  SIGPROF is excluded because we want to
 * be able to profile all of UML, not just the non-critical sections.  If
 * profiling is not thread-safe, then that is not my problem.  We can disable
 * profiling when SMP is enabled in that case.
 */
#define SIGIO_BIT 0
#define SIGIO_MASK (1 << SIGIO_BIT)

#define SIGVTALRM_BIT 1
#define SIGVTALRM_MASK (1 << SIGVTALRM_BIT)

static int signals_enabled;
static unsigned int pending;

void sig_handler(int sig, struct sigcontext *sc)
{
	int enabled;

	enabled = signals_enabled;
	if (!enabled && (sig == SIGIO)) {
		pending |= SIGIO_MASK;
		return;
	}

	block_signals();

	sig_handler_common(sig, sc);

	set_signals(enabled);
}

static void real_alarm_handler(struct sigcontext *sc)
{
	struct uml_pt_regs regs;

	if (sc != NULL)
		copy_sc(&regs, sc);
	regs.is_user = 0;
	unblock_signals();
	timer_handler(SIGVTALRM, &regs);
}

void alarm_handler(int sig, struct sigcontext *sc)
{
	int enabled;

	enabled = signals_enabled;
	if (!signals_enabled) {
		pending |= SIGVTALRM_MASK;
		return;
	}

	block_signals();

	real_alarm_handler(sc);
	set_signals(enabled);
}

void timer_init(void)
{
	set_handler(SIGVTALRM, (__sighandler_t) alarm_handler,
		    SA_ONSTACK | SA_RESTART, SIGUSR1, SIGIO, SIGWINCH, -1);
}

void set_sigstack(void *sig_stack, int size)
{
	stack_t stack = ((stack_t) { .ss_flags	= 0,
				     .ss_sp	= (__ptr_t) sig_stack,
				     .ss_size 	= size - sizeof(void *) });

	if (sigaltstack(&stack, NULL) != 0)
		panic("enabling signal stack failed, errno = %d\n", errno);
}

void remove_sigstack(void)
{
	stack_t stack = ((stack_t) { .ss_flags	= SS_DISABLE,
				     .ss_sp	= NULL,
				     .ss_size	= 0 });

	if (sigaltstack(&stack, NULL) != 0)
		panic("disabling signal stack failed, errno = %d\n", errno);
}

void (*handlers[_NSIG])(int sig, struct sigcontext *sc);

void handle_signal(int sig, struct sigcontext *sc)
{
	unsigned long pending = 1UL << sig;

	do {
		int nested, bail;

		/*
		 * pending comes back with one bit set for each
		 * interrupt that arrived while setting up the stack,
		 * plus a bit for this interrupt, plus the zero bit is
		 * set if this is a nested interrupt.
		 * If bail is true, then we interrupted another
		 * handler setting up the stack.  In this case, we
		 * have to return, and the upper handler will deal
		 * with this interrupt.
		 */
		bail = to_irq_stack(&pending);
		if (bail)
			return;

		nested = pending & 1;
		pending &= ~1;

		while ((sig = ffs(pending)) != 0){
			sig--;
			pending &= ~(1 << sig);
			(*handlers[sig])(sig, sc);
		}

		/*
		 * Again, pending comes back with a mask of signals
		 * that arrived while tearing down the stack.  If this
		 * is non-zero, we just go back, set up the stack
		 * again, and handle the new interrupts.
		 */
		if (!nested)
			pending = from_irq_stack(nested);
	} while (pending);
}

extern void hard_handler(int sig);

void set_handler(int sig, void (*handler)(int), int flags, ...)
{
	struct sigaction action;
	va_list ap;
	sigset_t sig_mask;
	int mask;

	handlers[sig] = (void (*)(int, struct sigcontext *)) handler;
	action.sa_handler = hard_handler;

	sigemptyset(&action.sa_mask);

	va_start(ap, flags);
	while ((mask = va_arg(ap, int)) != -1)
		sigaddset(&action.sa_mask, mask);
	va_end(ap);

	if (sig == SIGSEGV)
		flags |= SA_NODEFER;

	action.sa_flags = flags;
	action.sa_restorer = NULL;
	if (sigaction(sig, &action, NULL) < 0)
		panic("sigaction failed - errno = %d\n", errno);

	sigemptyset(&sig_mask);
	sigaddset(&sig_mask, sig);
	if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
		panic("sigprocmask failed - errno = %d\n", errno);
}

int change_sig(int signal, int on)
{
	sigset_t sigset, old;

	sigemptyset(&sigset);
	sigaddset(&sigset, signal);
	if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, &old) < 0)
		return -errno;
	return !sigismember(&old, signal);
}

void block_signals(void)
{
	signals_enabled = 0;
	/*
	 * This must return with signals disabled, so this barrier
	 * ensures that writes are flushed out before the return.
	 * This might matter if gcc figures out how to inline this and
	 * decides to shuffle this code into the caller.
	 */
	barrier();
}

void unblock_signals(void)
{
	int save_pending;

	if (signals_enabled == 1)
		return;

	/*
	 * We loop because the IRQ handler returns with interrupts off.  So,
	 * interrupts may have arrived and we need to re-enable them and
	 * recheck pending.
	 */
	while(1) {
		/*
		 * Save and reset save_pending after enabling signals.  This
		 * way, pending won't be changed while we're reading it.
		 */
		signals_enabled = 1;

		/*
		 * Setting signals_enabled and reading pending must
		 * happen in this order.
		 */
		barrier();

		save_pending = pending;
		if (save_pending == 0)
			return;

		pending = 0;

		/*
		 * We have pending interrupts, so disable signals, as the
		 * handlers expect them off when they are called.  They will
		 * be enabled again above.
		 */

		signals_enabled = 0;

		/*
		 * Deal with SIGIO first because the alarm handler might
		 * schedule, leaving the pending SIGIO stranded until we come
		 * back here.
		 */
		if (save_pending & SIGIO_MASK)
			sig_handler_common(SIGIO, NULL);

		if (save_pending & SIGVTALRM_MASK)
			real_alarm_handler(NULL);
	}
}

int get_signals(void)
{
	return signals_enabled;
}

int set_signals(int enable)
{
	int ret;
	if (signals_enabled == enable)
		return enable;

	ret = signals_enabled;
	if (enable)
		unblock_signals();
	else block_signals();

	return ret;
}