[lldb-dev] Huge mangled names are causing long delays when loading symbol table symbols

[Greg Clayton via lldb-dev]

> On Jan 24, 2018, at 4:14 PM, Zachary Turner <zturner at google.com> wrote:
> 
> That's true, but shouldn't it be possible to demangle up until the last point you got something meaningful?  (I don't know the details of itanium mangling, just assuming this is possible)

anywhere you cut the string many things can go wrong. I think this would fall under the "start to demangle the string and if the output buffer goes over a certain length, abort the demangling which is solution #4 from my original email.

> 
> On Wed, Jan 24, 2018 at 3:54 PM Greg Clayton <clayborg at gmail.com <mailto:clayborg at gmail.com>> wrote:
> If you just cut off the string, then it might not demangle without an error if you truncate the mangled string at a specific point...
> 
>> On Jan 24, 2018, at 3:52 PM, Zachary Turner <zturner at google.com <mailto:zturner at google.com>> wrote:
>> 
>> What about doing a partial demangle?   Take at most 1024 (for example) characters from the mangled name, demangle that, and then display ... at the end.
>> 
>> On Wed, Jan 24, 2018 at 3:48 PM Greg Clayton via lldb-dev <lldb-dev at lists.llvm.org <mailto:lldb-dev at lists.llvm.org>> wrote:
>> I have an issue where I am debugging a C++ binary that is around 250MB in size. It contains some mangled names that are crazy:
>> 
>> _ZNK3shk6detail17CallbackPublisherIZNS_5ThrowERKNSt15__exception_ptr13exception_ptrEEUlOT_E_E9SubscribeINS0_9ConcatMapINS0_18CallbackSubscriberIZNS_6GetAllIiNS1_IZZNS_9ConcatMapIZNS_6ConcatIJNS1_IZZNS_3MapIZZNS_7IfEmptyIS9_EEDaS7_ENKUlS6_E_clINS1_IZZNS_4TakeIiEESI_S7_ENKUlS6_E_clINS1_IZZNS_6FilterIZNS_9ElementAtEmEUlS7_E_EESI_S7_ENKUlS6_E_clINS1_IZZNSL_ImEESI_S7_ENKUlS6_E_clINS1_IZNS_4FromINS0_22InfiniteRangeContainerIiEEEESI_S7_EUlS7_E_EEEESI_S6_EUlS7_E_EEEESI_S6_EUlS7_E_EEEESI_S6_EUlS7_E_EEEESI_S6_EUlS7_E_EESI_S7_ENKUlS6_E_clIS14_EESI_S6_EUlS7_E_EERNS1_IZZNSH_IS9_EESI_S7_ENKSK_IS14_EESI_S6_EUlS7_E0_EEEEESI_DpOT_EUlS7_E_EESI_S7_ENKUlS6_E_clINS1_IZNS_5StartIJZNS_4JustIJS19_S1C_EEESI_S1F_EUlvE_ZNS1K_IJS19_S1C_EEESI_S1F_EUlvE0_EEESI_S1F_EUlS7_E_EEEESI_S6_EUlS7_E_EEEESt6vectorIS6_SaIS6_EERKT0_NS_12ElementCountEbEUlS7_E_ZNSD_IiS1Q_EES1T_S1W_S1X_bEUlOS3_E_ZNSD_IiS1Q_EES1T_S1W_S1X_bEUlvE_EES1G_S1O_E25ConcatMapValuesSubscriberEEEDaS7_
>> 
>> This de-mangles to something that is 72MB in size and takes 280 seconds (try running "time c++filt -n" on the above string).
>> 
>> There are probably many symbols likes this in this binary. Currently lldb will de-mangle all names in the symbol table so that we can chop up the names so we know function base names and we might be able to classify a base name as a method or function for breakpoint categorization.
>> 
>> My questions is: how do we work around such issues in LLDB? A few solutions I can think of:
>> 1 - time each name demangle and if it takes too long somehow stop de-mangling similar symbols or symbols over a certain length?
>> 2 - allow a setting that says "don't de-mangle names that start with..." and the setting has a list of prefixes.
>> 3 - have a setting that turns off de-mangling symbols over a certain length all of the time with a default of something like 256 or 512
>> 4 - modify our FastDemangler to abort if the de-mangled string goes over a certain limit to avoid bad cases like this...
>> 
>> #1 would still mean we get a huge delay (like 280 seconds) when starting to debug this binary, but might prevent multiple symbols from adding to that delay...
>> 
>> #2 would require debugging debugging once and then knowing which symbols took a while to de-mangle. If we time each de-mangle, we can warn that there are large mangled names and print the mangled name so the user might know?
>> 
>> #3 would disable de-mangling of long names at the risk of not de-mangling names that are close to the limit
>> 
>> #4 requires that our FastDemangle code can decode the string mangled string. The fast de-mangler currently aborts on tricky de-mangling and we fall back onto cxa_demangle from the C++ library which doesn't not have a cutoff on length...
>> 
>> Can anyone else think of any other solutions?
>> 
>> Greg Clayton
>> 
>> 
>> 
>> 
>> 
>> 
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