Hi Enrico, Instead of trying function-evaluation c_str(), I decided to decode the information from fbstring_core fields. I got it working but have two questions for it.
type summary add -F data_formatter.folly_string_formatter -x "std::fbstring_core<char>" Here is the output: fr v -T small (std::string) small = "small" fr v -T small.store_ (std::fbstring_core<char>) small.store_ = None fr v -T small.store_.ml_ (std::fbstring_core<char>::MediumLarge) small.store_.ml_ = None Questions: 1. Even I only added formatter for std::fbstring_core<char> why does it work for std::string? 2. Why the later small.store_ and small.store_.ml_ will show summary None now? I would not expect the data formatter will happen to them. Btw: here is the implementation of fbstring_core https://github.com/facebook/folly/blob/master/folly/FBString.h Thanks Jeffrey On Wed, Apr 13, 2016 at 11:08 AM, Enrico Granata <egran...@apple.com> wrote: > In theory what you're doing looks like it should be supported. I am not > sure why your example is failing the way it is. > > Is your variable a global maybe? > > Also, using the variable name is the wrong thing to do. If you have a > class with a std::string member, the name is going to return the wrong > thing. You would want to at least use the expression path - and even then > there are some cases where we can't cons up a proper expression path. > > Sent from my iPhone > > On Apr 13, 2016, at 11:02 AM, Jeffrey Tan <jeffrey.fu...@gmail.com> wrote: > > I did a quick testing to call SBFrame.EvaluateExpression('string.c_str()') > for the summary. The result shows valobj.GetFrame() returns None so does > this mean this is not supported? > > def DoTest(valobj,internal_dict): > print "valobj: %s" % valobj > print "valobj.GetFrame(): %s" % valobj.GetFrame() > summaryValue = valobj.GetFrame().EvaluateExpression(valobj.name + > '.c_str()') > print "summaryValue: %s" % summaryValue > return 'Summary from c_str(): %s ' % summaryValue.GetSummary() > > type summary add -F DoTest -x "std::fbstring_core<char>" > > Output: > valobj.GetFrame(): No value > summaryValue: No value > valobj: (std::string) $6 = { > store_ = Summary from c_str(): None > } > > Jeffrey > > On Wed, Apr 13, 2016 at 10:11 AM, Jeffrey Tan <jeffrey.fu...@gmail.com> > wrote: > >> One quick question: do we support getting type summary string from >> inferior method call? After reading our own fbstring_core code, I found I >> need to mirror a lot of what fbstring_core.c_str() method is doing in >> python. I wonder if we can just call ${var.c_str()} as the type summary? I >> suspect one of the concern is side-effect(the inferior method may throw >> exception or cause problems) but I would not see why this can't be done. By >> allowing this we can keep the data formatter truth one copy(in source code) >> instead of potential out-of-sync(let say the std::string author decided to >> change it implementation, the python data formatter associated with it >> needs to be modified at the same time which is a maintain nightmare). >> >> Jeffrey >> >> On Thu, Apr 7, 2016 at 10:33 AM, Enrico Granata <egran...@apple.com> >> wrote: >> >>> >>> On Apr 6, 2016, at 7:31 PM, Jeffrey Tan <jeffrey.fu...@gmail.com> wrote: >>> >>> Thanks Enrico. This is very detailed! I will take a look. >>> Btw: originally, I was hoping that data formatter can be added without >>> changing the source code. Like giving a xml/json format file telling lldb >>> the memory layout/structure of the data structure, lldb can parse the >>> xml/json and deduce the formatting. This is approach used by data >>> visualizer in VS debugger: >>> https://msdn.microsoft.com/en-us/library/jj620914.aspx >>> This will make adding data formatter more extensible/flexible. Any >>> reason we did not take this approach? >>> >>> >>> The way I understand the Natvis system, it allows one to provide a bunch >>> of expressions that describe how the debugger would go about retrieving the >>> interesting data bits >>> This has the bonus of being really easy, since you’re writing code in >>> the same language/context of the types you’re formatting >>> On the other hand it has a few drawbacks, in terms of performance as >>> well as safety (imagine trying to run code on an object when said object is >>> in an incoherent state) >>> The LLDB approach, on the other hand, is that you should try to not run >>> code when providing these data formatters. In order to do that, we vend an >>> API that can do things such as retrieve child values, read memory, cast >>> values, …, all without code execution >>> Once you have this kind of API that is not expressed in your source >>> language, you might just as well describe it in a scripting language. Hence >>> were born the Python data formatters. >>> In order for us to gain even more performance for native system types >>> that we know we’re gonna run into all the time, we then switched a bunch of >>> the “mission critical” formatters from Python to C++ >>> The Python extension points are still available, as Jim pointed out, and >>> you are more than welcome to use those instead of modifying the debugger >>> core >>> >>> Jeffrey >>> >>> On Wed, Apr 6, 2016 at 11:49 AM, Enrico Granata <egran...@apple.com> >>> wrote: >>> >>>> >>>> On Apr 5, 2016, at 2:42 PM, Jeffrey Tan <jeffrey.fu...@gmail.com> >>>> wrote: >>>> >>>> Hi Enrico, >>>> >>>> Any suggestion/example how to add a data formatter for our own STL >>>> string? From the output below I can see we are using our own " >>>> *fbstring_core*" which I assume I need to write a type summary for >>>> this type: >>>> >>>> frame variable corpus -T >>>> (const string &const) corpus = error: summary string parsing error: { >>>> (std::*fbstring_core*<char>) store_ = { >>>> (std::*fbstring_core*<char>::(anonymous union)) = { >>>> (char [24]) small_ = "www" >>>> (std::fbstring_core<char>::MediumLarge) ml_ = { >>>> (char *) data_ = 0x0000000000777777 >>>> "H\x89U\xa8H\x89M\xa0L\x89E\x98H\x8bE\xa8H\x89��_U��D\x88e�H\x8bE\xa0H\x89��]U��H\x89�H\x8dE�H\x89�H\x89��� >>>> ��L\x8dm�H\x8bE\x98H\x89��IU��\x88]�L\x8be\xb0L\x89�� >>>> (std::size_t) size_ = 0 >>>> (std::size_t) capacity_ = 1441151880758558720 >>>> } >>>> } >>>> } >>>> } >>>> >>>> >>>> Admittedly, this is going to be a little vague since I haven’t really >>>> seen your code and I am only working off of one sample >>>> >>>> There’s going to be two parts to getting this to work: >>>> >>>> *Part 1 - Formatting fbstring_core* >>>> >>>> At a glance, an fbstring_core<char> can be backed by two >>>> representations. A “small” representation (a char array), and a >>>> “medium/large" representation (a char* + a size) >>>> I assume that the way you tell one from the other is >>>> >>>> if (size == 0) small >>>> else medium-large >>>> >>>> If my assumption is not correct, you’ll need to discover what the >>>> correct discriminator logic is - the class has to know, and so do you :-) >>>> >>>> Armed with that knowledge, look in lldb >>>> source/Plugins/Language/CPlusPlus/Formatters/LibCxx.cpp >>>> There’s a bunch of code that deals with formatting llvm’s libc++ >>>> std::string - which follows a very similar logic to your class >>>> >>>> ExtractLibcxxStringInfo() is the function that handles discovering >>>> which layout the string uses - where the data lives - and how much data >>>> there is >>>> >>>> Once you have told yourself how much data there is (the size) and where >>>> it lives (array or pointer), LibcxxStringSummaryProvider() has the >>>> easy task - it sets up a StringPrinter, tells it how much data to print, >>>> where to get it from, and then delegates the StringPrinter to do the grunt >>>> work >>>> StringPrinter is a nifty little tool - it can handle generating >>>> summaries for different kinds of strings (UTF8? UTF16? we got it - is a \0 >>>> a terminator? what quote character would you like? …) - you point it at >>>> some data, set up a few options, and it will generate a printable >>>> representation for you - if your string type is doing anything out of the >>>> ordinary, let’s talk - I am definitely open to extending StringPrinter to >>>> handle even more magic >>>> >>>> *Part 2 - Teaching std::string that it can be backed by an >>>> fbstring_core* >>>> >>>> At the end of part 1, you’ll probably end up with a >>>> FBStringCoreSummaryProvider() - now you need to teach LLDB about it >>>> The obvious thing you could do would be to go in CPlusPlusLanguage >>>> ::GetFormatters() add a LoadFBStringFormatter(g_category) to it - and >>>> then imitate - say - LoadLibCxxFormatters() >>>> >>>> AddCXXSummary(cpp_category_sp, lldb_private::formatters:: >>>> FBStringCoreSummaryProvider, “fbstringcore summary provider", >>>> ConstString(“std::fbstring_core<.+>"), stl_summary_flags, true); >>>> >>>> That will work - but what you would see is: >>>> >>>> (const string &const) corpus = error: summary string parsing error: { >>>> (std::*fbstring_core*<char>) store_ = “www" >>>> >>>> >>>> You wanna do >>>> >>>> (lldb) log enable lldb formatters >>>> (lldb) frame variable -T corpus >>>> >>>> It will list one or more typenames - the most specific one is the one >>>> you like (e.g. for libc++ we get std::__1::string - this is how we tell >>>> ourselves this is the std::string from libc++) >>>> Once you find that typename, you’ll make a new formatter - >>>> FBStringSummaryProvider() - and register that formatter with that very >>>> specific typename >>>> >>>> All that FBStringSummaryProvider() has to do is get the “store_” member >>>> (ValueObject::GetChildMemberWithName() is your friend) - and pass it down >>>> to FBStringCoreSummaryProvider() >>>> >>>> >>>> I understand this may seem a little convoluted and arcane at first - >>>> but feel free to ask more questions, and I’ll try to help out! >>>> >>>> Thanks. >>>> Jeffrey >>>> >>>> On Mon, Mar 28, 2016 at 11:38 AM, Enrico Granata <egran...@apple.com> >>>> wrote: >>>> >>>>> This is kind of orthogonal to your problem, but the reason why you are >>>>> not seeing the kind of simplified printing Greg is suggesting, is because >>>>> your std::string doesn’t look like any of the kinds we recognize >>>>> >>>>> Specifically, LLDB data formatters work by matching against type >>>>> names, and once they recognize a typename, then they try to inspect the >>>>> variable in order to grab a summary >>>>> In your example, your std::string exposes a layout that we are not >>>>> handling - hence we bail out of the formatter and we fall back to the raw >>>>> view >>>>> >>>>> If you want pretty printing to work, you’ll need to write a data >>>>> formatter >>>>> >>>>> There are a few avenues. The obvious easy one is to extend the >>>>> existing std::string formatter to recognize your type’s internal layout. >>>>> If one were signing up for more infrastructure work, they could decide >>>>> to try and detect shared library loads and load formatters that match with >>>>> whatever libraries are being loaded. >>>>> >>>>> On Mar 28, 2016, at 9:47 AM, Greg Clayton via lldb-dev < >>>>> lldb-dev@lists.llvm.org> wrote: >>>>> >>>>> So you need to be prepared to escape any text that can have special >>>>> characters. A "std::string" or any container can contain special >>>>> characters. If you are encoding stuff into JSON, you will either need to >>>>> escape any special characters, or hex encode the string into ASCII hex >>>>> bytes. >>>>> >>>>> In debuggers we often get bogus data because variables are not >>>>> initialized, but the compiler tells us that a variable is valid in address >>>>> range [0x1000-0x2000), but it actually is [0x1200-0x2000). If we read a >>>>> variable in this case, a std::string might contain bogus data and the >>>>> bytes >>>>> might not make sense. So you always have to be prepared for bad data. >>>>> >>>>> If we look at: >>>>> >>>>> store_ = { >>>>> = { >>>>> small_ = "www" >>>>> ml_ = (data_ = >>>>> >>>>> "��UH\x89�H�}�H\x8bE�]ÐUH\x89�H��H\x89}�H\x8bE�H\x89��~\xb4��\x90��UH\x89�SH\x83�H\x89}�H�u�H�E�H���\x9e���H\x8b\x18H\x8bE�H���O\xb4��H\x89ƿ\b", >>>>> size_ = 0, capacity_ = 1441151880758558720) >>>>> } >>>>> } >>>>> } >>>>> >>>>> We can see the "size_" is zero, and capacity_ is 1441151880758558720 >>>>> (which is 0x1400000000000000). "data_" seems to be some random pointer. >>>>> >>>>> On MacOSX, we have a special formatting code that displays std::string >>>>> in CPlusPlusLanguage.cpp that gets installed in the LoadLibCxxFormatters() >>>>> or LoadLibStdcppFormatters() functions with code like: >>>>> >>>>> lldb::TypeSummaryImplSP std_string_summary_sp(new >>>>> CXXFunctionSummaryFormat(stl_summary_flags, >>>>> lldb_private::formatters::LibcxxStringSummaryProvider, "std::string >>>>> summary >>>>> provider")); >>>>> >>>>> cpp_category_sp->GetTypeSummariesContainer()->Add(ConstString("std::__1::string"), >>>>> std_string_summary_sp); >>>>> >>>>> Special flags are set on std::string to say "don't show children of >>>>> this and just show a summary" So if a std::string contained "hello". So >>>>> for >>>>> the following code: >>>>> >>>>> std::string h ("hello"); >>>>> >>>>> You should just see: >>>>> >>>>> (lldb) fr var h >>>>> (std::__1::string) h = "hello" >>>>> >>>>> If you take a look at the normal value in the raw we see: >>>>> >>>>> (lldb) fr var --raw h >>>>> (std::__1::string) h = { >>>>> __r_ = { >>>>> std::__1::__libcpp_compressed_pair_imp<std::__1::basic_string<char, >>>>> std::__1::char_traits<char>, std::__1::allocator<char> >::__rep, >>>>> std::__1::allocator<char>, 2> = { >>>>> __first_ = { >>>>> = { >>>>> __l = { >>>>> __cap_ = 122511465736202 >>>>> __size_ = 0 >>>>> __data_ = 0x0000000000000000 >>>>> } >>>>> __s = { >>>>> = { >>>>> __size_ = '\n' >>>>> __lx = '\n' >>>>> } >>>>> __data_ = { >>>>> [0] = 'h' >>>>> [1] = 'e' >>>>> [2] = 'l' >>>>> [3] = 'l' >>>>> [4] = 'o' >>>>> [5] = '\0' >>>>> [6] = '\0' >>>>> [7] = '\0' >>>>> [8] = '\0' >>>>> [9] = '\0' >>>>> [10] = '\0' >>>>> [11] = '\0' >>>>> [12] = '\0' >>>>> [13] = '\0' >>>>> [14] = '\0' >>>>> [15] = '\0' >>>>> [16] = '\0' >>>>> [17] = '\0' >>>>> [18] = '\0' >>>>> [19] = '\0' >>>>> [20] = '\0' >>>>> [21] = '\0' >>>>> [22] = '\0' >>>>> } >>>>> } >>>>> __r = { >>>>> __words = { >>>>> [0] = 122511465736202 >>>>> [1] = 0 >>>>> [2] = 0 >>>>> } >>>>> } >>>>> } >>>>> } >>>>> } >>>>> } >>>>> } >>>>> >>>>> So the main question is why are our "std::string" formatters not >>>>> kicking in for you. That comes down to a typename match, or the format of >>>>> the string isn't what the formatter is expecting. >>>>> >>>>> But again, since you std::string can contain anything, you will need >>>>> to escape any and all text that is encoded into JSON to ensure it doesn't >>>>> contain anything JSON can't deal with. >>>>> >>>>> On Mar 27, 2016, at 9:20 PM, Jeffrey Tan via lldb-dev < >>>>> lldb-dev@lists.llvm.org> wrote: >>>>> >>>>> Thanks Siva. All the DW_TAG_member related errors seems to go away >>>>> after patching with your fix. The current problem is handling the >>>>> decoding. >>>>> >>>>> Here is the correct decoding from gdb whic might be useful: >>>>> (gdb) p corpus >>>>> $3 = (const std::string &) @0x7fd133cfb888: { >>>>> static npos = 18446744073709551615, store_ = { >>>>> static kIsLittleEndian = <optimized out>, >>>>> static kIsBigEndian = <optimized out>, { >>>>> small_ = "www", '\000' <repeats 20 times>, "\024", ml_ = { >>>>> data_ = 0x777777 <std::_Any_data::_M_access<void >>>>> folly::fibers::Baton::waitFiber<folly::fibers::FirstArgOf<facebook::servicerouter::RequestDispatcherBase<facebook::servicerouter::ThriftDispatcher>::prepareForSelection(facebook::servicerouter::DispatchContext&)::{lambda(folly::fibers::Promise<facebook::servicerouter::RequestDispatcherBase<facebook::servicerouter::ThriftDispatcher>::prepareForSelection(facebook::servicerouter::DispatchContext&)::SelectionResult>)#1}, >>>>> void>::type::value_type >>>>> folly::fibers::await<facebook::servicerouter::RequestDispatcherBase<facebook::servicerouter::ThriftDispatcher>::prepareForSelection(facebook::servicerouter::DispatchContext&)::{lambda(folly::fibers::Promise<facebook::servicerouter::RequestDispatcherBase<facebook::servicerouter::ThriftDispatcher>::prepareForSelection(facebook::servicerouter::DispatchContext&)::SelectionResult>)#1}>(folly::fibers::FirstArgOf&&)::{lambda()#1}>(folly::fibers::FiberManager&, >>>>> folly::fibers::FirstArgOf<folly::fibers::FirstArgOf<facebook::servicerouter::RequestDispatcherBase<facebook::servicerouter::ThriftDispatcher>::prepareForSelection(facebook::servicerouter::DispatchContext&)::{lambda(folly::fibers::Promise<facebook::servicerouter::RequestDispatcherBase<facebook::servicerouter::ThriftDispatcher>::prepareForSelection(facebook::servicerouter::DispatchContext&)::SelectionResult>)#1}, >>>>> void>::type::value_type >>>>> folly::fibers::await<facebook::servicerouter::RequestDispatcherBase<facebook::servicerouter::ThriftDispatcher>::prepareForSelection(facebook::servicerouter::DispatchContext&)::{lambda(folly::fibers::Promise<facebook::servicerouter::RequestDispatcherBase<facebook::servicerouter::ThriftDispatcher>::prepareForSelection(facebook::servicerouter::DispatchContext&)::SelectionResult>)#1}>(folly::fibers::FirstArgOf&&)::{lambda()#1}, >>>>> void>::type::value_type)::{lambda(folly::fibers::Fiber&)#1}*>() const+25> >>>>> "\311\303UH\211\345H\211}\370H\213E\370]ÐUH\211\345H\203\354\020H\211}\370H\213E\370H\211\307\350~\264\312\377\220\311\303UH\211\345SH\203\354\030H\211}\350H\211u\340H\213E\340H\211\307\350\236\377\377\377H\213\030H\213E\350H\211\307\350O\264\312\377H\211ƿ\b", >>>>> size_ = 0, >>>>> capacity_ = 1441151880758558720}}}} >>>>> >>>>> Utf-16 does not seem to decode it, while 'latin-1' does: >>>>> >>>>> '\xc9'.decode('utf-16') >>>>> >>>>> Traceback (most recent call last): >>>>> File "<stdin>", line 1, in <module> >>>>> File >>>>> "/mnt/gvfs/third-party2/python/55c1fd79d91c77c95932db31a4769919611c12bb/2.7.8/centos6-native/da39a3e/lib/python2.7/encodings/utf_16.py", >>>>> line 16, in decode >>>>> return codecs.utf_16_decode(input, errors, True) >>>>> UnicodeDecodeError: 'utf16' codec can't decode byte 0xc9 in position >>>>> 0: truncated data >>>>> >>>>> '\xc9'.decode('latin-1') >>>>> >>>>> u'\xc9' >>>>> >>>>> Instead of guessing what kind of decoding I should use, I would use >>>>> 'ensure_ascii=False' to prevent the crash for now. >>>>> >>>>> I tried to reproduce this crash, but it seems that the crash might be >>>>> related with some internal stl implementation we are using. I will see if >>>>> I >>>>> can narrow down to a small repro later. >>>>> >>>>> Thanks >>>>> Jeffrey >>>>> >>>>> On Sun, Mar 27, 2016 at 2:49 PM, Siva Chandra <sivachan...@gmail.com> >>>>> wrote: >>>>> On Sat, Mar 26, 2016 at 11:58 PM, Jeffrey Tan <jeffrey.fu...@gmail.com> >>>>> wrote: >>>>> >>>>> Btw: after patching with Siva's fix http://reviews.llvm.org/D18008, >>>>> the >>>>> first field 'small_' is fixed, however the second field 'ml_' still >>>>> emits >>>>> garbage: >>>>> >>>>> (lldb) fr v corpus >>>>> (const string &const) corpus = error: summary string parsing error: { >>>>> store_ = { >>>>> = { >>>>> small_ = "www" >>>>> ml_ = (data_ = >>>>> >>>>> "��UH\x89�H�}�H\x8bE�]ÐUH\x89�H��H\x89}�H\x8bE�H\x89��~\xb4��\x90��UH\x89�SH\x83�H\x89}�H�u�H�E�H���\x9e���H\x8b\x18H\x8bE�H���O\xb4��H\x89ƿ\b", >>>>> size_ = 0, capacity_ = 1441151880758558720) >>>>> } >>>>> } >>>>> } >>>>> >>>>> >>>>> Do you still see the DW_TAG_member related error? >>>>> >>>>> A wild (and really wild at that) guess: Is it utf16 data that is being >>>>> decoded as utf8? >>>>> >>>>> As David Blaikie mentioned on the other thread, it would really help >>>>> if you provide us with a minimal example to repro this. Atleast, repro >>>>> instructions. >>>>> >>>>> _______________________________________________ >>>>> lldb-dev mailing list >>>>> lldb-dev@lists.llvm.org >>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev >>>>> >>>>> >>>>> _______________________________________________ >>>>> lldb-dev mailing list >>>>> lldb-dev@lists.llvm.org >>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev >>>>> >>>>> >>>>> >>>>> Thanks, >>>>> *- Enrico* >>>>> 📩 egranata@.com ☎️ 27683 >>>>> >>>>> >>>> >>>> >>>> Thanks, >>>> *- Enrico* >>>> 📩 egranata@.com ☎️ 27683 >>>> >>>> >>> >>> >>> Thanks, >>> *- Enrico* >>> 📩 egranata@.com ☎️ 27683 >>> >>> >> >
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