[sanitizer] Fix __sanitizer_syscall_post_epoll_wait

[vitalybuka]

Summary

Syscall return number of initialized events which
needs to be used for unposoning.

[vitalybuka]

clang-format

[vitalybuka]

rebase

[morehouse]

LGTM

compiler-rt/lib/sanitizer_common/sanitizer_common_syscalls.inc

 
 PRE_SYSCALL(epoll_wait)
 (long epfd, void *events, long maxevents, long timeout) {}
 
 POST_SYSCALL(epoll_wait)
 (long res, long epfd, void *events, long maxevents, long timeout) {
   if (res >= 0) {
     if (events)
-      POST_WRITE(events, struct_epoll_event_sz);
+      POST_WRITE(events, res * struct_epoll_event_sz);
   }
 }
 
 PRE_SYSCALL(epoll_pwait)
 (long epfd, void *events, long maxevents, long timeout,
  const kernel_sigset_t *sigmask, long sigsetsize) {
   if (sigmask)
     PRE_READ(sigmask, sigsetsize);
 }
 
 POST_SYSCALL(epoll_pwait)
 (long res, long epfd, void *events, long maxevents, long timeout,
  const void *sigmask, long sigsetsize) {
   if (res >= 0) {
     if (events)
-      POST_WRITE(events, struct_epoll_event_sz);
+      POST_WRITE(events, res * struct_epoll_event_sz);
   }
 }
 
 PRE_SYSCALL(gethostname)(void *name, long len) {}
 
 POST_SYSCALL(gethostname)(long res, void *name, long len) {
   if (res >= 0) {
     if (name)

compiler-rt/test/msan/Linux/syscalls.cpp

 // RUN: %clangxx_msan -O0 %s -o %t && %run %t 2>&1
 // RUN: %clangxx_msan -O3 %s -o %t && %run %t 2>&1
 
 #include <assert.h>
 #include <errno.h>
 #include <glob.h>
 #include <stdio.h>
 #include <string.h>
 
 #include <linux/aio_abi.h>
 #include <signal.h>
+#include <sys/epoll.h>
 #include <sys/ptrace.h>
 #include <sys/stat.h>
 #include <sys/uio.h>
 
 #include <sanitizer/linux_syscall_hooks.h>
 #include <sanitizer/msan_interface.h>
 
 /* Test the presence of __sanitizer_syscall_ in the tool runtime, and general
int main(int argc, char *argv[]) {
   __msan_poison(buf, sizeof(buf));
   __sanitizer_syscall_post_socketpair(0, 0, 0, 0, (int *)buf);
   assert(__msan_test_shadow(buf, sizeof(buf)) == 2 * sizeof(int));
 
   __msan_poison(buf, sizeof(buf));
   __sanitizer_syscall_post_sigaltstack(0, nullptr, (stack_t *)buf);
   assert(__msan_test_shadow(buf, sizeof(buf)) == sizeof(stack_t));
 
+  __msan_poison(buf, sizeof(buf));
+  long max_events = sizeof(buf) / sizeof(epoll_event);
+  __sanitizer_syscall_pre_epoll_wait(0, buf, max_events, 0);
+  __sanitizer_syscall_post_epoll_wait(max_events, 0, buf, max_events, 0);
+  assert(__msan_test_shadow(buf, sizeof(buf)) == max_events * sizeof(epoll_event));
+
+  __msan_poison(buf, sizeof(buf));
+  sigset_t sigset = {};
+  __sanitizer_syscall_pre_epoll_pwait(0, buf, max_events, 0, &sigset, sizeof(sigset));
+  __sanitizer_syscall_post_epoll_pwait(max_events, 0, buf, max_events, 0, &sigset, sizeof(sigset));
+  assert(__msan_test_shadow(buf, sizeof(buf)) == max_events * sizeof(epoll_event));
+
   return 0;
 }