[compiler-rt/profile] Hide __llvm_profile_raw_version

Hide __llvm_profile_raw_version so as not to resolve reference from a
dependent shared object.  Since libclang_rt.profile is added later in
the command line, a definition of __llvm_profile_raw_version is not
included if it is provided from an earlier object, e.g.  from a shared
dependency.

This causes an extra dependence edge where if libA.so depends on libB.so
and both are coverage-instrumented, libA.so uses libB.so's definition of
__llvm_profile_raw_version.  This leads to a runtime link failure if the
libB.so available at runtime does not provide this symbol (but provides
the other dependent symbols).  Such a scenario can occur in Android's
mainline modules.
E.g.:
  ld -o libB.so libclang_rt.profile-x86_64.a
  ld -o libA.so -l B libclang_rt.profile-x86_64.a

libB.so has a global definition of __llvm_profile_raw_version.  libA.so
uses libB.so's definition of __llvm_profile_raw_version.  At runtime,
libB.so may not be coverage-instrumented (i.e. not export
__llvm_profile_raw_version) so runtime linking of libA.so will fail.

Marking this symbol as hidden forces each binary to use the definition
of __llvm_profile_raw_version from libclang_rt.profile.

Differential Revision: https://reviews.llvm.org/D111759

Author: pirama-arumuga-nainar

compiler-rt/lib/profile/InstrProfiling.h

@@ -301,14 +301,11 @@ void __llvm_profile_set_dumped();
 COMPILER_RT_VISIBILITY extern int INSTR_PROF_PROFILE_RUNTIME_VAR;
 
 /*!
- * This variable is defined in InstrProfiling.c. Its main purpose is to
- * encode the raw profile version value and other format related information
- * such as whether the profile is from IR based instrumentation. The variable
- * is defined as weak so that compiler can emit an overriding definition
- * depending on user option.  Since we don't support mixing FE and IR based
- * data in the same raw profile data file (in other words, shared libs and
- * main program are expected to be instrumented in the same way), there is
- * no need for this variable to be hidden.
+ * This variable is defined in InstrProfilingVersionVar.c as a hidden symbol.
+ * Its main purpose is to encode the raw profile version value and other format
+ * related information such as whether the profile is from IR based
+ * instrumentation. The variable is defined as weak so that compiler can emit an
+ * overriding definition depending on user option.
  */
 extern uint64_t INSTR_PROF_RAW_VERSION_VAR; /* __llvm_profile_raw_version */
 

compiler-rt/lib/profile/InstrProfilingVersionVar.c

@@ -14,4 +14,5 @@
  * user has not specified one. Set this up by moving the runtime's copy of this
  * symbol to an object file within the archive.
  */
-COMPILER_RT_WEAK uint64_t INSTR_PROF_RAW_VERSION_VAR = INSTR_PROF_RAW_VERSION;
+COMPILER_RT_VISIBILITY COMPILER_RT_WEAK uint64_t INSTR_PROF_RAW_VERSION_VAR =
+    INSTR_PROF_RAW_VERSION;