[lldb-dev] Problem formatting class types

[Zachary Turner via lldb-dev]

Note that I also tried this with a a linux / DWARF executable and had the
same result.

On Fri, Oct 26, 2018 at 3:21 AM Zachary Turner <zturner at google.com> wrote:

> Hello,
>
> I've got this code:
>
> class Class {
>   int x = 0;
>   short y = 1;
>   char z = 'z';
> } C;
>
> int main(int argc, char **argv) {
>   __debugbreak();
>   return 0;
> }
>
> and I run the following LLDB session:
>
> lldb.exe -f foo.exe
> (lldb) target create "foo.exe"
> Current executable set to 'foo.exe' (x86_64).
> (lldb) run
> Process 24604 launched: 'foo.exe' (x86_64)
> Process 24604 stopped
> * thread #1, stop reason = Exception 0x80000003 encountered at address
> 0x7ff70a0b1017
>     frame #0: 0x00007ff70a0b1018 foo.exe`main(argc=-1123614720,
> argv=0x00007ff70a0b1000) at foo.cpp:19
>    16
>    17   int main(int argc, char **argv) {
>    18     __debugbreak();
> -> 19     return 0;
>    20   }
> (lldb) p C
> (Class) $0 =
> (lldb)
>
> The issue is, of course, that it doesn't display the members of the class
> C.  The type support in PDB is fine, so it's not that.  For example:
>
> (lldb) type lookup Class
> class Class {
>     int x;
>     short y;
>     char z;
> }
>
> And it can definitely find C in memory:
>
> (lldb) p &C
> (Class *) $1 = 0x00007ff70a0b3000
>
> Instead, the issue seems to be related to the value object formatter.  I
> tried to track this down but this code is pretty complicated.  However,
> there are two issues that I was able to discover:
>
> 1) It's using the objective C class formatter.  Obviously I'm not using
> objective C, so that seems wrong right off the bat.  Specifically, the
> "Synthetic children front end" is the ObjCClassSyntheticChildrenFrontEnd.
>
> 2) Because of #1, when it calls CalculateNumChildren() in Cocoa.cpp, it
> returns 0.  I would expect it to be calling some function somewhere that
> returns 3, because there are 3 members of the class.
>
> What's strange is that I don't see anything in the CPlusPlusLanguage
> plugin that provides a SyntheticChildrenFrontEnd that examines the
> CxxRecordDecl and looks for children, so I don't know how this is supposed
> to work anywhere.  But I know it must work somewhere, so I assume I'm just
> missing something and I need to find out the right place to hook A up to B
> and things will just work.
>
> Any pointers on what the expected code path that this should be taking is,
> so I can try to figure out where I might be going off path?
>
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