[Libunwind-devel] How can multiple instruction pointers points to same function?

[Ali Nakipoğlu]

I'm writing a utility and Im using libunwind for walking call stack as
suggested in http://www.nongnu.org/libunwind/man/libunwind(3).html

void backtrace (void) {
  unw_cursor_t cursor;
  unw_context_t context;
  unw_word_t instructionPointer;

  unw_getcontext(&context);
  unw_init_local(&cursor, &context);
  while (unw_step(&cursor) > 0) {
    unw_get_reg(&cursor, UNW_REG_IP, &instructionPointer);

    if( isUnique( instructionPointer ) ) {
       char name[ 255 ] = {'\0'};
       unw_word_t offset;

       unw_get_proc_name( &cursor, name, sizeof( name ), &offset );

       record( instructionPointer, name );
    }
  }}

( I took isUnique and record out to make reading easier, you can find them
them below )

I was expecting to have only one *instructionPointer* per *name*. But, I'm
getting more than one:

139894098909857 -> dl_open_worker139894098910090 ->
dl_open_worker..... (more lines)..... (more lines)..... (more
lines)139893967715894 -> __do_global_ctors_aux139893966114427 ->
_init139893961300241 ->
_ZN8Shiboken6Module6createEPKcPv139893967235163 ->
initQtCore139894093505625 ->
_PyImport_LoadDynamicModule139893961275008 ->
_ZN8Shiboken11Conversions4initEv139893961237083 ->
_ZN8Shiboken4initEv139893961275033 ->
_ZN8Shiboken11Conversions4initEv139893961275059 ->
_ZN8Shiboken11Conversions4initEv139893961275084 ->
_ZN8Shiboken11Conversions4initEv139893961275113 ->
_ZN8Shiboken11Conversions4initEv139893961275138 ->
_ZN8Shiboken11Conversions4initEv139893961275160 ->
_ZN8Shiboken11Conversions4initEv139893961275182 ->
_ZN8Shiboken11Conversions4initEv139893961275208 ->
_ZN8Shiboken11Conversions4initEv139893961275233 ->
_ZN8Shiboken11Conversions4initEv139893961275255 ->
_ZN8Shiboken11Conversions4initEv

I probably misunderstand something and wasn't able to find relevant
information. Is there a correct way to do this? Any explanation to why this
is happening?

bool isUnique( uint64_t instructionPointer  )
{
  std::unique_lock<std::mutex> scopedLock( mutex );
  // instructionPointerSet is unordered_set<uint64_t>
  return instructionPointerSet.insert( instructionPointer ).second;
}

void record( uint64_t instructionPointer, const char * name )
{
  std::unique_lock<std::mutex> scopedLock( mutex );
  // symbols is std::vector<std::pair<uint64_t, std::string>>
  symbols.push_back( std::make_tuple(  instructionPointer,
std::string(name) ) );
}

Many thanks.

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