[lldb-dev] Problem formatting class types
Zachary Turner via lldb-dev
lldb-dev at lists.llvm.org
Fri Oct 26 03:21:09 PDT 2018
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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