raw_fd_ostream: Make file handles non-inheritable by default

[labath]

Summary

This makes the file descriptors on unix platform non-inheritable by default
(O_CLOEXEC). I have also added a file open flag F_Inheritable to override this
behavior if necessary. If the platform supports O_CLOEXEC flag, we will use it
to set the descriptor flag during open(2). If the flag is not available, we will
revert to the (racy) fcntl(2) call.

There is no change in behavior on windows, as the handles were already
non-inheritable by default (but one can still use the new flag to make them
inheritable).

[aaron.ballman]

lib/Support/Unix/Path.inc

648 ↗

(On Diff #84819)

In general, please add && "something useful" so that people who trigger this assert have a chance to know what went wrong.

lib/Support/Windows/Path.inc

778 ↗

(On Diff #84819)

Please add parens around the argument.

[aaron.ballman]

Btw, I should note that the Windows code LGTM.

[labath]

After the round of comments, the patch has significantly decreased in size. :)

• I have removed the F_Inheritable flag, as we don't care about inheritable handles now
• I reverted the windows changes, as they already create non-inheritable handles
• I reverted the cmake code checking for O_CLOEXEC. I will watch out for buildbot emails to see if anything breaks.

I also added the O_CLOEXEC flag to openFileForRead(), for symmetry.

llvm/trunk/lib/Support/Unix/Path.inc

static bool hasProcSelfFD() {
   return Result;
 }
 #endif
 
 std::error_code openFileForRead(const Twine &Name, int &ResultFD,
                                 SmallVectorImpl<char> *RealPath) {
   SmallString<128> Storage;
   StringRef P = Name.toNullTerminatedStringRef(Storage);
-  while ((ResultFD = open(P.begin(), O_RDONLY)) < 0) {
+  while ((ResultFD = open(P.begin(), O_RDONLY | O_CLOEXEC)) < 0) {
     if (errno != EINTR)
       return std::error_code(errno, std::generic_category());
   }
   // Attempt to get the real name of the file, if the user asked
   if(!RealPath)
     return std::error_code();
   RealPath->clear();
 #if defined(F_GETPATH)

 }
 
 std::error_code openFileForWrite(const Twine &Name, int &ResultFD,
                             sys::fs::OpenFlags Flags, unsigned Mode) {
   // Verify that we don't have both "append" and "excl".
   assert((!(Flags & sys::fs::F_Excl) || !(Flags & sys::fs::F_Append)) &&
          "Cannot specify both 'excl' and 'append' file creation flags!");
 
-  int OpenFlags = O_CREAT;
+  int OpenFlags = O_CREAT | O_CLOEXEC;
 
   if (Flags & F_RW)
     OpenFlags |= O_RDWR;
   else
     OpenFlags |= O_WRONLY;
 
   if (Flags & F_Append)
     OpenFlags |= O_APPEND;