[lldb-dev] UnicodeDecodeError for serialize SBValue description
Jeffrey Tan via lldb-dev
lldb-dev at lists.llvm.org
Wed Apr 13 11:02:24 PDT 2016
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.fudan at 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 <egranata at apple.com>
> wrote:
>
>>
>> On Apr 6, 2016, at 7:31 PM, Jeffrey Tan <jeffrey.fudan at 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 <egranata at apple.com>
>> wrote:
>>
>>>
>>> On Apr 5, 2016, at 2:42 PM, Jeffrey Tan <jeffrey.fudan at 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 <egranata at 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 at 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 at 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 <sivachandra at gmail.com>
>>>> wrote:
>>>> On Sat, Mar 26, 2016 at 11:58 PM, Jeffrey Tan <jeffrey.fudan at 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 at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>>>>
>>>>
>>>> _______________________________________________
>>>> lldb-dev mailing list
>>>> lldb-dev at 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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