[profile] Skip mmap() if there are no counters

[vsk]

Summary

If there are no counters, an mmap() of the counters section would fail
due to the size argument being too small (EINVAL).

rdar://78175925

[phosek]

LGTM

compiler-rt/lib/profile/InstrProfilingFile.c

if (ProfileFileSize == 0) {
        * with the data in this process. */
       char *ProfileBuffer;
       if (mmapProfileForMerging(File, ProfileFileSize, &ProfileBuffer) == -1 ||
           munmap(ProfileBuffer, ProfileFileSize) == -1)
         return unlockProfile(&ProfileRequiresUnlock, File);
     }
   }
 
+  /* mmap() the profile counters so long as there is at least one counter.
+   * If there aren't any counters, mmap() would fail with EINVAL. */
+  if (CountersSize > 0) {
     int Fileno = fileno(File);
 
     /* Determine how much padding is needed before/after the counters and after
      * the names. */
     uint64_t PaddingBytesBeforeCounters, PaddingBytesAfterCounters,
         PaddingBytesAfterNames;
     __llvm_profile_get_padding_sizes_for_counters(
         DataSize, CountersSize, NamesSize, &PaddingBytesBeforeCounters,
         &PaddingBytesAfterCounters, &PaddingBytesAfterNames);
 
     uint64_t PageAlignedCountersLength =
         (CountersSize * sizeof(uint64_t)) + PaddingBytesAfterCounters;
     uint64_t FileOffsetToCounters =
         CurrentFileOffset + sizeof(__llvm_profile_header) +
         (DataSize * sizeof(__llvm_profile_data)) + PaddingBytesBeforeCounters;
 
     uint64_t *CounterMmap = (uint64_t *)mmap(
         (void *)CountersBegin, PageAlignedCountersLength, PROT_READ | PROT_WRITE,
         MAP_FIXED | MAP_SHARED, Fileno, FileOffsetToCounters);
     if (CounterMmap != CountersBegin) {
       PROF_ERR(
           "Continuous counter sync mode is enabled, but mmap() failed (%s).\n"
           "  - CountersBegin: %p\n"
           "  - PageAlignedCountersLength: %" PRIu64 "\n"
           "  - Fileno: %d\n"
           "  - FileOffsetToCounters: %" PRIu64 "\n",
           strerror(errno), CountersBegin, PageAlignedCountersLength, Fileno,
           FileOffsetToCounters);
     }
+  }
 
   if (ProfileRequiresUnlock)
     unlockProfile(&ProfileRequiresUnlock, File);
 #endif // defined(__Fuchsia__) || defined(_WIN32)
 }
 
 static const char *DefaultProfileName = "default.profraw";
 static void resetFilenameToDefault(void) {

compiler-rt/test/profile/ContinuousSyncMode/image-with-no-counters.c

+// REQUIRES: darwin
+
+// RUN: echo "static void dead_code(void) {}" > %t.dso.c
+// RUN: %clang_profgen -fcoverage-mapping -O3 -dynamiclib -o %t.dso.dylib %t.dso.c
+// RUN: %clang_profgen -fcoverage-mapping -O3 -o %t.exe %s %t.dso.dylib
+// RUN: env LLVM_PROFILE_FILE="%c%t.profraw" %run %t.exe 2>&1 | count 0
+// RUN: llvm-profdata show --counts --all-functions %t.profraw | FileCheck %s
+
+// CHECK: Total functions: 1
+
+int main() {}