Merge pull request iovisor#1002 from goldshtn/nested-symbols

cc: Handle nested functions correctly when resolving symbols

src/cc/bcc_syms.cc

@@ -190,16 +190,31 @@ bool ProcSyms::Module::find_addr(uint64_t addr, struct bcc_symbol *sym) {
  sym->offset = offset;
 
  auto it = std::upper_bound(syms_.begin(), syms_.end(), Symbol(nullptr, offset, 0));
- if (it != syms_.begin())
- --it;
- else
- it = syms_.end();
+ if (it == syms_.begin())
+ return false;
 
- if (it != syms_.end()
- && offset >= it->start && offset < it->start + it->size) {
- sym->name = it->name->c_str();
- sym->offset = (offset - it->start);
- return true;
+ // 'it' points to the symbol whose start address is strictly greater than
+ // the address we're looking for. Start stepping backwards as long as the
+ // current symbol is still below the desired address, and see if the end
+ // of the current symbol (start + size) is above the desired address. Once
+ // we have a matching symbol, return it. Note that simply looking at '--it'
+ // is not enough, because symbols can be nested. For example, we could be
+ // looking for offset 0x12 with the following symbols available:
+ // SYMBOL START SIZE END
+ // goo 0x0 0x6 0x0 + 0x6 = 0x6
+ // foo 0x6 0x10 0x6 + 0x10 = 0x16
+ // bar 0x8 0x4 0x8 + 0x4 = 0xc
+ // baz 0x16 0x10 0x16 + 0x10 = 0x26
+ // The upper_bound lookup will return baz, and then going one symbol back
+ // brings us to bar, which does not contain offset 0x12 and is nested inside
+ // foo. Going back one more symbol brings us to foo, which contains 0x12
+ // and is a match.
+ for (--it; offset >= it->start; --it) {
+ if (offset < it->start + it->size) {
+ sym->name = it->name->c_str();
+ sym->offset = (offset - it->start);
+ return true;
+ }
  }
 
  return false;