1// RUN: %clangxx -O1 %s -o %t && env TSAN_OPTIONS="flush_memory_ms=1 memory_limit_mb=1" %run %t 2>&1 | FileCheck %s
2
3// JVM uses SEGV to preempt threads. All threads do a load from a known address
4// periodically. When runtime needs to preempt threads, it unmaps the page.
5// Threads start triggering SEGV one by one. The signal handler blocks
6// threads while runtime does its thing. Then runtime maps the page again
7// and resumes the threads.
8// Previously this pattern conflicted with stop-the-world machinery,
9// because it briefly reset SEGV handler to SIG_DFL.
10// As the consequence JVM just silently died.
11
12// This test sets memory flushing rate to maximum, then does series of
13// "benign" SEGVs that are handled by signal handler, and ensures that
14// the process survive.
15
16#include <assert.h>
17#include <signal.h>
18#include <stdio.h>
19#include <stdlib.h>
20#include <string.h>
21#include <sys/mman.h>
22#include <unistd.h>
23
24unsigned long page_size;
25void *guard;
26
27void handler(int signo, siginfo_t *info, void *uctx) {
28 mprotect(addr: guard, len: page_size, PROT_READ | PROT_WRITE);
29}
30
31int main() {
32 page_size = sysconf(_SC_PAGESIZE);
33 struct sigaction a, old;
34 memset(s: &a, c: 0, n: sizeof(a));
35 memset(s: &old, c: 0, n: sizeof(old));
36 a.sa_sigaction = handler;
37 a.sa_flags = SA_SIGINFO;
38 sigaction(SIGSEGV, act: &a, oact: &old);
39
40 memset(s: &a, c: 0, n: sizeof(a));
41 sigaction(SIGSEGV, act: 0, oact: &a);
42 assert(a.sa_sigaction == handler);
43 assert(a.sa_flags & SA_SIGINFO);
44
45 guard = mmap(addr: 0, len: 3 * page_size, PROT_NONE, MAP_ANON | MAP_PRIVATE, fd: -1, offset: 0);
46 guard = (char*)guard + page_size; // work around a kernel bug
47 for (int i = 0; i < 1000000; i++) {
48 mprotect(addr: guard, len: page_size, PROT_NONE);
49 *(int*)guard = 1;
50 }
51 sigaction(SIGSEGV, act: &old, oact: 0);
52 fprintf(stderr, format: "DONE\n");
53}
54
55// CHECK: DONE
56

source code of compiler-rt/test/sanitizer_common/TestCases/Linux/signal_segv_handler.cpp