[llvm-dev] [LLD] Slow callstacks in gdb (original) (raw)

Rafael Avila de Espindola via llvm-dev llvm-dev at lists.llvm.org
Tue Nov 28 09:46:46 PST 2017

Martin Richtarsky <s at martinien.de> writes:

Hi,

Is the program being built by gcc or clang? gcc 6, but I can try clang. Are both using --gdb-index? Can you try lld trunk if so? No. Is any of the programs you tested open source? No. Here is some more info. I enabled "set verbose on" in gdb. With this setting, I'm getting DWARF errors in both versions when executing "bt" (linked by gold and lld), but the lld version has significantly more errors. These only appear in the lld version: (gdb) bt Reading in symbols for abc.cpp.... debugline address at offset 0x575128 is 0 [in module abc.so].... debugline address at offset 0x575141 is 0 [in module abc.so].... cannot get low and high bounds for subprogram DIE at 52844002... cannot get low and high bounds for subprogram DIE at 52844042... cannot get low and high bounds for subprogram DIE at 52844092... const value length mismatch for 'std::iosconstants::boolalpha', got 4, expected 0 _debug info gives command-line macro definition with non-zero line 13: MACRO _macro 'USEISOC95' is #undefined twice _macro `STDCLIMITMACROS' redefined at... Member function "~basicistream" (offset 28792309) is virtual but the vtable offset is not specified...

Maybe gdb needs to fall back to slower line number resolution because e.g. low and high bounds cannot be retrieved and debuglineaddress is 0?

It is hard to know without a reproducible. I tried gdb on clang itself build with both clang and gcc and linked with gold and lld. I could not reproduce the slowdown, but I was using trunk lld.

Cheers, Rafael

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