1 /* SPDX-License-Identifier: LGPL-2.1+ */
12 #define SIGBUS_QUEUE_MAX 64
14 static struct sigaction old_sigaction;
15 static unsigned n_installed = 0;
17 /* We maintain a fixed size list of page addresses that triggered a
18 SIGBUS. We access with list with atomic operations, so that we
19 don't have to deal with locks between signal handler and main
20 programs in possibly multiple threads. */
22 static void* volatile sigbus_queue[SIGBUS_QUEUE_MAX];
23 static volatile sig_atomic_t n_sigbus_queue = 0;
25 static void sigbus_push(void *addr) {
30 /* Find a free place, increase the number of entries and leave, if we can */
31 for (u = 0; u < SIGBUS_QUEUE_MAX; u++)
32 if (__sync_bool_compare_and_swap(&sigbus_queue[u], NULL, addr)) {
33 __sync_fetch_and_add(&n_sigbus_queue, 1);
37 /* If we can't, make sure the queue size is out of bounds, to
38 * mark it as overflow */
45 if (c > SIGBUS_QUEUE_MAX) /* already overflow */
48 if (__sync_bool_compare_and_swap(&n_sigbus_queue, c, c + SIGBUS_QUEUE_MAX))
53 int sigbus_pop(void **ret) {
65 if (_unlikely_(c >= SIGBUS_QUEUE_MAX))
68 for (u = 0; u < SIGBUS_QUEUE_MAX; u++) {
71 addr = sigbus_queue[u];
75 if (__sync_bool_compare_and_swap(&sigbus_queue[u], addr, NULL)) {
76 __sync_fetch_and_sub(&n_sigbus_queue, 1);
84 static void sigbus_handler(int sn, siginfo_t *si, void *data) {
91 if (si->si_code != BUS_ADRERR || !si->si_addr) {
92 assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0);
97 ul = (unsigned long) si->si_addr;
98 ul = ul / page_size();
99 ul = ul * page_size();
100 aligned = (void*) ul;
102 /* Let's remember which address failed */
103 sigbus_push(aligned);
105 /* Replace mapping with an anonymous page, so that the
106 * execution can continue, however with a zeroed out page */
107 assert_se(mmap(aligned, page_size(), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0) == aligned);
110 void sigbus_install(void) {
111 struct sigaction sa = {
112 .sa_sigaction = sigbus_handler,
113 .sa_flags = SA_SIGINFO,
118 if (n_installed == 1)
119 assert_se(sigaction(SIGBUS, &sa, &old_sigaction) == 0);
124 void sigbus_reset(void) {
126 if (n_installed <= 0)
131 if (n_installed == 0)
132 assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0);