wrong usages of sem_open in the libFuzzer

[tomsun.0.7]

Summary

Fixed two non-standard usages of sem_open in the libFuzzer library and
one NetBSD-related modification with test script.

• The return value to indicate error should be SEM_FAILED instead of (void *)-1 (please refer to "RETURN VALUE" section in this page). Actually, SEM_FAILED != (void *)-1 holds in NetBSD.
• The SharedMemoryRegion::SemName function should return name starting with slash. Because the behaviour of name which does not start with slash is unspecified as the "DESCRIPTION" section specified:

If name does not begin with the <slash> character, the effect is implementation-defined.

• The length of name is limited to 14 in NetBSD, it is suggested to reduce the length of equivalence server name in the test script.

[krytarowski]

It looks good to me, but I will wait for the final word from @vitalybuka

BTW.
We usually want to see a diff as a result of git diff -U9999 for larger context.
Also the description shall be manually formatted for restricted number of columns,
otherwise we will get very long lines in a commit description.

[tomsun.0.7]

In D46622#1092416, @krytarowski wrote:

It looks good to me, but I will wait for the final word from @vitalybuka

BTW.
We usually want to see a diff as a result of git diff -U9999 for larger context.
Also the description shall be manually formatted for restricted number of columns,
otherwise we will get very long lines in a commit description.

Updated, thanks for the suggestions!

[kcc]

I don't mind, but just a FYI: it's likely that I will delete this code in near future.

lib/fuzzer/FuzzerShmemPosix.cpp

35

please explain in a comment

[kcc]

LGTM

lib/fuzzer/FuzzerShmemPosix.cpp

 namespace fuzzer {
 
 std::string SharedMemoryRegion::Path(const char *Name) {
   return DirPlusFile(TmpDir(), Name);
 }
 
 std::string SharedMemoryRegion::SemName(const char *Name, int Idx) {
   std::string Res(Name);
+  // When passing a name without a leading <slash> character to
+  // sem_open, the behaviour is unspecified in POSIX. Add a leading
+  // <slash> character for the name if there is no such one.
+  if (!Res.empty() && Res[0] != '/')
+    Res.insert(Res.begin(), '/');
   return Res + (char)('0' + Idx);
 }
 
 bool SharedMemoryRegion::Map(int fd) {
   Data =
       (uint8_t *)mmap(0, kShmemSize, PROT_WRITE | PROT_READ, MAP_SHARED, fd, 0);
   if (Data == (uint8_t*)-1)
     return false;
   return true;
 }
 
 bool SharedMemoryRegion::Create(const char *Name) {
   int fd = open(Path(Name).c_str(), O_CREAT | O_RDWR, 0777);
   if (fd < 0) return false;
   if (ftruncate(fd, kShmemSize) < 0) return false;
   if (!Map(fd))
     return false;
   for (int i = 0; i < 2; i++) {
     sem_unlink(SemName(Name, i).c_str());
     Semaphore[i] = sem_open(SemName(Name, i).c_str(), O_CREAT, 0644, 0);
-    if (Semaphore[i] == (void *)-1)
+    if (Semaphore[i] == SEM_FAILED)
       return false;
   }
   IAmServer = true;
   return true;
 }
 
 bool SharedMemoryRegion::Open(const char *Name) {
   int fd = open(Path(Name).c_str(), O_RDWR);
   if (fd < 0) return false;
   struct stat stat_res;
   if (0 != fstat(fd, &stat_res))
     return false;
   assert(stat_res.st_size == kShmemSize);
   if (!Map(fd))
     return false;
   for (int i = 0; i < 2; i++) {
     Semaphore[i] = sem_open(SemName(Name, i).c_str(), 0);
-    if (Semaphore[i] == (void *)-1)
+    if (Semaphore[i] == SEM_FAILED)
       return false;
   }
   IAmServer = false;
   return true;
 }
 
 bool SharedMemoryRegion::Destroy(const char *Name) {
   return 0 == unlink(Path(Name).c_str());

test/fuzzer/equivalence-signals.test

 # Run EquivalenceATest against itself with a small timeout
 # to stress the signal handling and ensure that shmem doesn't mind
 # the signals.
 UNSUPPORTED: freebsd
 
 # The test is not supported on Darwin
 UNSUPPORTED: darwin
 
 RUN: %cpp_compiler %S/EquivalenceATest.cpp -o %t-EquivalenceATest
-RUN: %t-EquivalenceATest -timeout=1 -run_equivalence_server=EQUIV_SIG_TEST & export APID=$!
+RUN: %t-EquivalenceATest -timeout=1 -run_equivalence_server=EQ_SIG_TEST & export APID=$!
 RUN: sleep 3
-RUN: %t-EquivalenceATest -timeout=1 -use_equivalence_server=EQUIV_SIG_TEST -runs=500000 2>&1
+RUN: %t-EquivalenceATest -timeout=1 -use_equivalence_server=EQ_SIG_TEST -runs=500000 2>&1
 RUN: kill -9 $APID