Set hidden attribute on lprofMergeValueProfData

[apazos]

Summary

The changes in https://reviews.llvm.org/D44847 cause load time failure
due to lprofMergeValueProfData in Android libs enabled with profile generation:

"dlopen failed: cannot locate symbol "lprofMergeValueProfData" referenced by..."

Marking lprofMergeValueProfData as hidden so the correct in-module definition
is picked by the linker.

[davidxl]

Test case?

[apazos]

A test would need to dump the contents of the symbol table and verify the hidden attribute for that symbol. Do you have something else in mind?

[davidxl]

Can you write a test case with a shared library that is instrumented and write a main program with dlopen to demonstrate the problem if the fix is not there?

[apazos]

I observed the issue with instrumented libs in Android. I have not been successful in reducing a test case that would fail on x86 linux.
I can write a test case that shows I can do a dlopen/dlsym of lprofMergeValueProfData from a different library, but with the hidden attribute set on the function, the dlsym call will fail.
Shouldn't we prevent lprofMergeValueProfData from being accessed outside a module?

[apazos]

I added a test case to verify the fix prevents lprofMergeValueProfData from another module from being accessed.

[davidxl]

lgtm

lib/profile/InstrProfilingMergeFile.c

 #include "InstrProfilingInternal.h"
 #include "InstrProfilingUtil.h"
 
 #define INSTR_PROF_VALUE_PROF_DATA
 #include "InstrProfData.inc"
 
 /* Merge value profile data pointed to by SrcValueProfData into
  * in-memory profile counters pointed by to DstData.  */
+COMPILER_RT_VISIBILITY
 void lprofMergeValueProfData(ValueProfData *SrcValueProfData,
                              __llvm_profile_data *DstData) {
   unsigned I, S, V, DstIndex = 0;
   InstrProfValueData *VData;
   ValueProfRecord *VR = getFirstValueProfRecord(SrcValueProfData);
   for (I = 0; I < SrcValueProfData->NumValueKinds; I++) {
     VData = getValueProfRecordValueData(VR);
     unsigned SrcIndex = 0;

test/profile/Inputs/instrprof-value-prof-visibility.c

+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#ifdef DLOPEN_FUNC_DIR
+#include <dlfcn.h>
+#endif
+
+int __llvm_profile_runtime = 0;
+int __llvm_profile_write_file();
+void __llvm_profile_reset_counters(void);
+void __llvm_profile_initialize_file(void);
+struct __llvm_profile_data;
+struct ValueProfData;
+void lprofMergeValueProfData(struct ValueProfData *, struct __llvm_profile_data *);
+/* Force the vp merger module to be linked in.  */
+void *Dummy = &lprofMergeValueProfData;
+
+void callee1() {}
+void callee2() {}
+
+typedef void (*FP)(void);
+FP Fps[2] = {callee1, callee2};
+
+int main(int argc, char *argv[]) {
+  __llvm_profile_initialize_file();
+  __llvm_profile_write_file();
+  __llvm_profile_reset_counters();
+
+#ifdef DLOPEN_FUNC_DIR
+  void *Handle = dlopen(DLOPEN_FUNC_DIR"/func.shared", RTLD_NOW);
+  if (!Handle) {
+    fprintf(stderr, "unable to open '" DLOPEN_FUNC_DIR "/func.shared': %s\n",
+            dlerror());
+    return EXIT_FAILURE;
+  }
+
+ // This tests that lprofMergeValueProfData is not accessed
+ // from outside a module
+  void (*SymHandle)(struct ValueProfData *, struct __llvm_profile_data *) =
+    (void (*)(struct ValueProfData *, struct __llvm_profile_data *))dlsym(
+    Handle, "lprofMergeValueProfData");
+  if (SymHandle) {
+    fprintf(stderr,
+            "should not be able to lookup symbol 'lprofMergeValueProfData': %s\n",
+            dlerror());
+    return EXIT_FAILURE;
+  }
+
+  dlclose(Handle);
+
+#endif
+
+  Fps[0]();
+  Fps[1]();
+
+  __llvm_profile_write_file();
+  __llvm_profile_reset_counters();
+
+  return EXIT_SUCCESS;
+}
+

test/profile/Linux/instrprof-value-prof-visibility.test

+# This tests that lprofMergeValueProfData is not accessed from outside a module
+RUN: mkdir -p %t.d
+RUN: %clang_profgen -o %t.d/func.shared -fPIC -shared -fuse-ld=gold -mllvm --enable-value-profiling=true %S/../Inputs/instrprof-value-prof-visibility.c -fdata-sections -ffunction-sections -fuse-ld=gold -Wl,--gc-sections
+RUN: %clang_profgen -o %t.d/main -fuse-ld=gold -mllvm --enable-value-profiling=true  -DDLOPEN_FUNC_DIR=\"%t.d\" %S/../Inputs/instrprof-value-prof-visibility.c -fdata-sections -ffunction-sections -fuse-ld=gold -Wl,--gc-sections
+RUN: env LLVM_PROFILE_FILE=%t.profraw %run %t.d/main
+