[PGO] Ensure profile section symbols are created (linux)

- This is to handle a corner case where profile lib is linked
  in but non of the modules are instrumented (On linux, since
  we avoided the overhead to emit runtime hook use functions so
  this is the side effect of that size optimization).
- Added a profile runtime test case to cover all scenarios of
  shared library builds. 

Differential Revision: http://reviews.llvm.org/D14468

llvm-svn: 253098

1 files changed, 4 insertions, 0 deletions

diff --git a/compiler-rt/lib/profile/InstrProfilingBuffer.c b/compiler-rt/lib/profile/InstrProfilingBuffer.c
index e587932da0a..620c1755baa 100644
--- a/compiler-rt/lib/profile/InstrProfilingBuffer.c
+++ b/compiler-rt/lib/profile/InstrProfilingBuffer.c
@@ -79,6 +79,10 @@ int __llvm_profile_write_buffer_internal(
 
   /* Create the header. */
   __llvm_profile_header Header;
+
+  if (!DataSize)
+    return 0;
+
   Header.Magic = __llvm_profile_get_magic();
   Header.Version = __llvm_profile_get_version();
   Header.DataSize = DataSize;