de9ccd5f-6521-4b39-ab30-f4e04ed39258
commented
2 years ago I've stumbled across a simpler case that doesn't require boost or fPIC/fPIE. Here Derived is a template that is instantiated with 2 structs, one global and another one local to a function. In the first case the dynamic type is detected correctly, in the second case it is not.
test.cpp
struct Base { virtual ~Base() {} };
template
struct OuterFoo { };
int main() { struct InnerFoo { };
Derived<OuterFoo> od;
Base* ob = &od;
Derived<InnerFoo> id;
Base* ib = &id;
return 0;}
Command line:
$ clang++ -g test.cpp -o test
$ lldb-12 -f test -o "b 27" -o "run" -o "p ob" -o "p ib" -o quit
...
Process 2849427 launched: '/home/brd/work/misc/tests/lldb_base_class_issue2/test' (x86_64)
(lldb) p ob
(Derived ) $0 = 0x00007fffffffda70
(lldb) p ib
(Base ) $1 = 0x00007fffffffda60
Symbol table:
$ lldb-12 -f test -o "image dump symtab" -o quit | grep Foo
[ 11] 12 Code 0x0000000000401190 0x0000000000000034 0x00000002 Derived::Derived()
[ 12] 13 Code 0x00000000004011f0 0x0000000000000028 0x00000002 Derived::~Derived()
[ 13] 14 Code 0x00000000004011d0 0x000000000000001b 0x00000002 Derived::~Derived()
[ 14] 15 Data 0x00000000004020d0 0x0000000000000018 0x00000001 typeinfo for Derived
[ 15] 16 Data 0x00000000004020b0 0x000000000000001b 0x00000001 typeinfo name for Derived
[ 16] 17 Data 0x0000000000402090 0x0000000000000020 0x00000001 vtable for Derived
[ 24] 26 Code 0x0000000000401260 0x000000000000001b 0x00000022 Derived::~Derived()
[ 26] 28 Data 0x0000000000402028 0x0000000000000014 0x00000021 typeinfo name for Derived
[ 29] 31 Code 0x0000000000401220 0x0000000000000034 0x00000022 Derived::Derived()
[ 43] 45 Code 0x00000000004012a0 0x0000000000000028 0x00000022 Derived::~Derived()
[ 51] 53 Data 0x0000000000402058 0x0000000000000018 0x00000021 typeinfo for Derived
[ 55] 57 Data 0x0000000000402008 0x0000000000000020 0x00000021 vtable for Derived
Versions:
$ clang++ --version Ubuntu clang version 12.0.0-3ubuntu1~21.04.2 Target: x86_64-pc-linux-gnu Thread model: posix InstalledDir: /usr/bin
jimingham
Extended Description
If I compile the following code with fPIC or fPIE:
include <boost/asio/io_context.hpp>
include <boost/asio/strand.hpp>
void foo(boost::asio::io_context& context) { boost::asio::io_context::strand s{context}; }
struct Base { virtual ~Base() {} };
struct Derived: Base { Derived(int zzz) : zzz(zzz) {}
};
int main() { Derived d{123}; Base* b = &d;
}
and run it in lldb, "print b" will print: (Base *) $0 = 0x00007fffffffdc58
But if I compile it without fPIC/fPIE, or modify the code slightly, e.g. by commenting out the unused function "foo", I get the expected output: (Derived *) $0 = 0x00007fffffffdc58
The behaviour doesn't depend on the compiler; I tried clang 11.0 and gcc-10.2 and the result was the same.
Since the code depends on boost, I'm attaching the preprocessed version too.
I compile it as follows: $ clang++ -g -fPIC test_preproc_clang.cpp -o test -lpthread
Clang version: Ubuntu clang version 11.0.0-2
LLDB version: lldb version 12.0.0 (git@github.com:llvm/llvm-project.git revision d28af7c654d8db0b68c175db5ce212d74fb5e9bc) clang revision d28af7c654d8db0b68c175db5ce212d74fb5e9bc llvm revision d28af7c654d8db0b68c175db5ce212d74fb5e9bc
boost version: 1.73.0