Hide some symbols to avoid a crash on shutdown when using code coverage

[sylvestre.ledru]

Summary

gcov / gcda-based profiling crashes when shared libraries are unloaded

Patch by Benoit Belley and test by Marco Castelluccio for Firefox

See https://bugs.llvm.org/show_bug.cgi?id=27224 & https://bugzilla.mozilla.org/show_bug.cgi?id=1401230

[davidxl]

Can you add a test case with shared libraries?

[belleyb]

Autodesk would also like to see this fix merged into LLVM 5.0.1 and we also agree about the importance of having a regression tests.

@sylvestre.ledru : Is someone on the Firefox team working on writing a unit test for this ? Shall we jump-in and try to help ?

[belleyb]

@sylvestre.ledru Thanks for the test!

[sylvestre.ledru]

please thank Marco :)

[sylvestre.ledru]

@davidxl David, is that ok with you? Can you sign off this change? Thanks

[sylvestre.ledru]

I added two more reviewers as we would like to get that in trunk before 6.0 branches.

[marco-c]

The change was already positively reviewed with the request for a test, which has been written since then.

lib/profile/GCDAProfiling.c

 \*===----------------------------------------------------------------------===*/
 
 #include "InstrProfilingUtil.h"
+#include "InstrProfilingPort.h" /* for COMPILER_RT_VISIBILITY */
 
 #include <errno.h>
 #include <fcntl.h>

  * profiling enabled will emit to a different file. Only one file may be
  * started at a time.
  */
+COMPILER_RT_VISIBILITY
 void llvm_gcda_start_file(const char *orig_filename, const char version[4],
                           uint32_t checksum) {
   const char *mode = "r+b";

 /* Given an array of pointers to counters (counters), increment the n-th one,
  * where we're also given a pointer to n (predecessor).
  */
+COMPILER_RT_VISIBILITY
 void llvm_gcda_increment_indirect_counter(uint32_t *predecessor,
                                           uint64_t **counters) {
   uint64_t *counter;

 #endif
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_gcda_emit_function(uint32_t ident, const char *function_name,
                              uint32_t func_checksum, uint8_t use_extra_checksum,
                              uint32_t cfg_checksum) {

     write_string(function_name);
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_gcda_emit_arcs(uint32_t num_counters, uint64_t *counters) {
   uint32_t i;
   uint64_t *old_ctrs = NULL;

 #endif
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_gcda_summary_info() {
   const uint32_t obj_summary_len = 9; /* Length for gcov compatibility. */
   uint32_t i;

 #endif
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_gcda_end_file() {
   /* Write out EOF record. */
   if (output_file) {

 #endif
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_register_writeout_function(writeout_fn fn) {
   struct writeout_fn_node *new_node = malloc(sizeof(struct writeout_fn_node));
   new_node->fn = fn;

   }
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_writeout_files() {
   struct writeout_fn_node *curr = writeout_fn_head;
 

   }
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_delete_writeout_function_list() {
   while (writeout_fn_head) {
     struct writeout_fn_node *node = writeout_fn_head;

   writeout_fn_head = writeout_fn_tail = NULL;
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_register_flush_function(flush_fn fn) {
   struct flush_fn_node *new_node = malloc(sizeof(struct flush_fn_node));
   new_node->fn = fn;

   }
 }
 
+COMPILER_RT_VISIBILITY
 void __gcov_flush() {
   struct flush_fn_node *curr = flush_fn_head;
 

   }
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_delete_flush_function_list() {
   while (flush_fn_head) {
     struct flush_fn_node *node = flush_fn_head;

   flush_fn_head = flush_fn_tail = NULL;
 }
 
+COMPILER_RT_VISIBILITY
 void llvm_gcov_init(writeout_fn wfn, flush_fn ffn) {
   static int atexit_ran = 0;