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Tweak our symbol resolution again #336

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Tweak our symbol resolution again #336

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36 changes: 31 additions & 5 deletions src/pystack/_pystack/unwinder.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -352,6 +352,7 @@ AbstractUnwinder::dwarfModuleAddrDie(Dwarf_Addr pc_adjusted, Dwfl_Module* mod, D

struct ModuleArg
{
Dwfl* dwfl;
const char* symbol;
const char* modulename;
remote_addr_t addr;
Expand Down Expand Up @@ -382,10 +383,35 @@ module_callback(
for (int i = 0; i < n_syms; i++) {
const char* sname = dwfl_module_getsym_info(mod, i, &sym, &addr, nullptr, nullptr, nullptr);
if (strcmp(sname, module_arg->symbol) == 0) {
module_arg->addr = addr;
LOG(INFO) << "Symbol '" << sname << "' found at address " << std::hex << std::showbase
<< addr;
return DWARF_CB_ABORT;
Dwfl_Module* actual_module = dwfl_addrmodule(module_arg->dwfl, addr);
if (actual_module != mod) {
// Save this address if it's the first one we've seen, but keep looking for a match
// that resolves to the expected module.
if (!module_arg->addr) {
module_arg->addr = addr;
}
const char* actual_module_name = dwfl_module_info(
actual_module,
nullptr,
nullptr,
nullptr,
nullptr,
nullptr,
nullptr,
nullptr);
LOG(INFO) << "Symbol '" << sname << "' found at address " << std::hex << std::showbase
<< addr << " which falls in "
<< (actual_module_name ? actual_module_name : "a non-file-backed mapping")
<< " rather than the expected module " << module_arg->modulename
<< " so we will keep looking for a better match";
return DWARF_CB_OK;
} else {
// Otherwise, stop looking and use this match.
module_arg->addr = addr;
LOG(INFO) << "Symbol '" << sname << "' found at address " << std::hex << std::showbase
<< addr;
return DWARF_CB_ABORT;
}
}
}
return DWARF_CB_OK;
Expand All @@ -395,7 +421,7 @@ remote_addr_t
AbstractUnwinder::getAddressforSymbol(const std::string& symbol, const std::string& modulename) const
{
LOG(DEBUG) << "Trying to find address for symbol " << symbol;
ModuleArg arg = {symbol.c_str(), modulename.c_str(), 0};
ModuleArg arg = {Dwfl(), symbol.c_str(), modulename.c_str(), 0};
if (dwfl_getmodules(Dwfl(), module_callback, &arg, 0) == -1) {
throw UnwinderError("Failed to fetch modules!");
}
Expand Down
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