[PGO] Delay directory creation until write time

[davidxl]

Summary

Some process starts as root but drops the privileges later. Profile runtime currently eagerly creates profile file directory on program start up. This can cause problems later when profiling APIs (such as set filename, cleanup dir etc) are used to do profile dumping when the process privilege is dropped -- the directory can not be cleaned up before/after profile dumping.

In this patch, the dir creation is delayed until profile writing time when merge mode is on. No other external behavior changes should be expected.

[vsk]

Makes sense, I was thinking of something like this for a test;

// RUN: %clang_profgen -o %t %s
// RUN: env LLVM_PROFILE_FILE="%t.d/%m.profraw"
// RUN: %run %t %t.d

#include <unistd.h>

int main(int argc, char **argv) {
  if (access(argv[1], F_OK) == 0)
    return 1; // %t.d should not exist yet.
  return errno == ENOENT;
}

Edit: you'd probably have to make sure %t.d doesn't exist before running the test.

[xur]

why limit to merge mode?
non-merge mode also exhibits the problem mentioned.

[davidxl]

Added test case suggested by Vedant.

[vsk]

Thanks, LGTM.

[xur]

LGTM too.

lib/profile/InstrProfilingFile.c

 
   /* Now start merging */
   __llvm_profile_merge_from_buffer(ProfileBuffer, ProfileFileSize);
   (void)munmap(ProfileBuffer, ProfileFileSize);
 
   return 0;
 }
 
+/* Create the directory holding the file, if needed. */
+static void createProfileDir(const char *Filename) {
+  size_t Length = strlen(Filename);
+  if (lprofFindFirstDirSeparator(Filename)) {
+    char *Copy = (char *)COMPILER_RT_ALLOCA(Length + 1);
+    strncpy(Copy, Filename, Length + 1);
+    __llvm_profile_recursive_mkdir(Copy);
+  }
+}
+
 /* Open the profile data for merging. It opens the file in r+b mode with
  * file locking.  If the file has content which is compatible with the
  * current process, it also reads in the profile data in the file and merge
  * it with in-memory counters. After the profile data is merged in memory,
  * the original profile data is truncated and gets ready for the profile
  * dumper. With profile merging enabled, each executable as well as any of
  * its instrumented shared libraries dump profile data into their own data file.
 */
 static FILE *openFileForMerging(const char *ProfileFileName) {
   FILE *ProfileFile;
   int rc;
 
+  createProfileDir(ProfileFileName);
   ProfileFile = lprofOpenFileEx(ProfileFileName);
   if (!ProfileFile)
     return NULL;
 
   rc = doProfileMerging(ProfileFile);
   if (rc || COMPILER_RT_FTRUNCATE(ProfileFile, 0L) ||
       fseek(ProfileFile, 0L, SEEK_SET) == -1) {
     PROF_ERR("Profile Merging of file %s failed: %s\n", ProfileFileName,

   int Length;
 
   Length = getCurFilenameLength();
   FilenameBuf = (char *)COMPILER_RT_ALLOCA(Length + 1);
   Filename = getCurFilename(FilenameBuf);
   if (!Filename)
     return;
 
-  /* Create the directory holding the file, if needed. */
-  if (lprofFindFirstDirSeparator(Filename)) {
-    char *Copy = (char *)COMPILER_RT_ALLOCA(Length + 1);
-    strncpy(Copy, Filename, Length + 1);
-    __llvm_profile_recursive_mkdir(Copy);
-  }
-
   /* By pass file truncation to allow online raw profile
    * merging. */
   if (lprofCurFilename.MergePoolSize)
     return;
 
+  createProfileDir(Filename);
+
   /* Truncate the file.  Later we'll reopen and append. */
   File = fopen(Filename, "w");
   if (!File)
     return;
   fclose(File);
 }
 
 static const char *DefaultProfileName = "default.profraw";