Merge pull request iovisor#1377 from palmtenor/ksym_segfault

Avoid potential SEGFAULT when resolving Kernel symbols

src/cc/bcc_syms.cc

@@ -61,21 +61,25 @@ void KSyms::refresh() {
 bool KSyms::resolve_addr(uint64_t addr, struct bcc_symbol *sym, bool demangle) {
  refresh();
 
- if (syms_.empty()) {
- sym->name = nullptr;
- sym->demangle_name = nullptr;
- sym->module = nullptr;
- sym->offset = 0x0;
- return false;
+ std::vector<Symbol>::iterator it;
+
+ if (syms_.empty())
+ goto unknown_symbol;
+
+ it = std::upper_bound(syms_.begin(), syms_.end(), Symbol("", addr));
+ if (it != syms_.begin()) {
+ it--;
+ sym->name = (*it).name.c_str();
+ if (demangle)
+ sym->demangle_name = sym->name;
+ sym->module = "kernel";
+ sym->offset = addr - (*it).addr;
+ return true;
  }
 
- auto it = std::upper_bound(syms_.begin(), syms_.end(), Symbol("", addr)) - 1;
- sym->name = (*it).name.c_str();
- if (demangle)
- sym->demangle_name = sym->name;
- sym->module = "kernel";
- sym->offset = addr - (*it).addr;
- return true;
+unknown_symbol:
+ memset(sym, 0, sizeof(struct bcc_symbol));
+ return false;
 }
 
 bool KSyms::resolve_name(const char *_unused, const char *name,