[lldb-dev] RTTI does not work stable in LLDB.

[Robinson, Paul via lldb-dev]

So is LLDB expecting the name in the DWARF info to match the demangled name of the vtable pointer?  The DWARF spec does not really specify what the name of a template instantiation should be, and in particular does not *want* to specify whether it matches any given demangler's opinion of the name.
--paulr

From: lldb-dev [mailto:lldb-dev-bounces at lists.llvm.org] On Behalf Of Greg Clayton via lldb-dev
Sent: Monday, February 06, 2017 11:08 AM
To: Greg Clayton
Cc: lldb-dev at lists.llvm.org
Subject: Re: [lldb-dev] RTTI does not work stable in LLDB.

So I found the problem. This is a compiler bug. The DWARF for this type looks like:

0x000065da:     TAG_structure_type [112] *
                 AT_containing_type( {0x0000000000006628} )
                 AT_name( "derived0<int, int, 1024>" )
                 AT_byte_size( 0x08 )
                 AT_decl_file( "/private/tmp/main.cpp" )
                 AT_decl_line( 9 )

But all of the type info in the symbol table has has the type named as "derived0<int, int, 1024u>”. Note the extra “u” that follows 1024. This stops LLDB from being able to lookup the type correctly so we can show the dynamic type. In LLDB we check the first pointer inside of a class to see if it is a symbol whose name is “vtable for TYPENAME”. If it is, we lookup the type “TYPENAME” to find it. In this case we try to lookup "derived0<int, int, 1024u>” and we fail since the DWARF has it as "derived0<int, int, 1024>”.

I have filed a radar on the compiler here at Apple for the fix.

Greg



On Feb 6, 2017, at 10:22 AM, Greg Clayton via lldb-dev <lldb-dev at lists.llvm.org<mailto:lldb-dev at lists.llvm.org>> wrote:

I am looking at this now. I will let you know what I find.

Greg

On Feb 6, 2017, at 10:00 AM, Roman Popov <ripopov at gmail.com<mailto:ripopov at gmail.com>> wrote:

Yes, that was my thought.

FYI, checked in GDB: it's working correctly on this testcase showing correct dynamic type in both cases.

2017-02-06 9:48 GMT-08:00 Greg Clayton <gclayton at apple.com<mailto:gclayton at apple.com>>:
You have found a bug. It should be reporting this correctly but it isn’t. I verified it fails on MacOSX.

Greg Clayton

On Feb 5, 2017, at 1:19 PM, Roman Popov via lldb-dev <lldb-dev at lists.llvm.org<mailto:lldb-dev at lists.llvm.org>> wrote:

Hello,
I'm observing very strange LLDB behavior: it does not always shows a correct dynamic type when I ask for.

Originally I was working with LLDB 3.9, but it looks like trunk version behaves the same strange way.

I was able to capture this behavior in a small code snippet:

#include <iostream>
#include <typeinfo>

using namespace std;

struct base_type {  virtual ~base_type(){} };

template <class T1, class T2, unsigned SIZE>
struct derived0 : base_type {};

template <class T1, class T2>
struct derived1 : base_type {};

int main(int argc, char ** argv) {

    base_type * bptr0 = new derived0<int, int, 1024>();
    base_type * bptr1 = new derived1<int, int >();

    cout << typeid(*bptr0).name() << endl;
    cout << typeid(*bptr1).name() << endl;

    return 0;
}


lldb --version
lldb version 5.0.0 (http://llvm.org/svn/llvm-project/lldb/trunk revision 293398)
  clang revision 293398
  llvm revision 293398


Testing in LLDB:
(lldb) break set --file main.cpp --line 22

(lldb) expression -d no-run --  bptr1
(derived1<int, int> *) $2 = 0x0000000000614c40

(lldb) expression -d no-run --  bptr0
(base_type *) $3 = 0x0000000000614c20


Can someone explain me why for bptr0 I dont get a  derived0<int, int, 1024> * as I expected?


Thanks,
Roman
_______________________________________________
lldb-dev mailing list
lldb-dev at lists.llvm.org<mailto: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<mailto:lldb-dev at lists.llvm.org>
http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/lldb-dev/attachments/20170206/cb0afbc2/attachment-0001.html>