Your message dated Mon, 04 Aug 2025 13:16:36 -0400
with message-id <[email protected]>
and subject line Closing bug
has caused the Debian Bug report #188627,
regarding gdb: problems demangling vtable symbols
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--
188627: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=188627
Debian Bug Tracking System
Contact [email protected] with problems
--- Begin Message ---
Package: gdb
Version: 5.3-2
Severity: important
gdb fails to demangle vtables when multiple C++ ABIs are in use in the
same application.
It is possible for a single application to use multiple stdc++ libraries
with different ABIs as long as the objects using the different
ABIs/libraries are seperated by a dlopen() call. I encountered this
situation when an application I was working on was compiled with
g++-2.95 and a library was doing a dlopen of a library that depended on
xlibmesa3-dev, which was compiled with g++-3.2
gdb emits lots of errors like the following and occasionally crashes in
"call" and "print" commands that require correct resolution of a vtable:
warning: can't find linker symbol for virtual table for `Derived' value
warning: can't find linker symbol for virtual table for `Derived' value
warning: can't find linker symbol for virtual table for `Derived' value
To reproduce:
#!/bin/bash
cat <<END_OF_Makefile >Makefile
default: main
mylib.o: mylib.cpp
g++-3.2 -g -c -fPIC -o mylib.o mylib.cpp
libmylib.so: mylib.o
g++-3.2 -shared -o libmylib.so mylib.o
main.o: main.cpp
g++-2.95 -g -c -o main.o main.cpp
main: main.o libmylib.so
g++-2.95 -rdynamic -ldl -o main main.o
clean:
rm -f main.o mylib.o main libmylib.so
END_OF_makefile
cat <<END_OF_mylib >mylib.cpp
#include <iostream>
extern "C" void print()
{
std::cout << "print() at " << __FILE__ << ":" << __LINE__ <<
std::endl;
}
END_OF_mylib
cat <<END_OF_main >main.cpp
#include <iostream>
#include <dlfcn.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>
class Base {
public:
explicit Base(int value = 0) : baseData(value) {}
virtual ~Base();
int get_base() const { return baseData; }
private:
int baseData;
};
class Derived : public Base {
public:
explicit Derived(int value, int base_value = 0)
: Base(base_value), derivedData(value) {}
virtual ~Derived();
void print() const;
private:
int derivedData;
};
Base::~Base()
{ cout << "~Base()" << endl; }
Derived::~Derived()
{ cout << "~Derived()" << endl; }
void Derived::print() const {
cout << get_base() << " " << derivedData << endl;
}
void* load_lib()
{
char buffer[PATH_MAX];
getcwd( buffer, PATH_MAX );
strncat( buffer, "/libmylib.so", PATH_MAX );
void* handle = dlopen( buffer, RTLD_NOW );
if ( !handle ) {
cout << dlerror() << endl;
exit(1);
}
return handle;
}
typedef void(*void_func)(void);
int main()
{
Derived object(5);
void* handle = load_lib();
void_func f_ptr = (void_func)dlsym( handle, "print" );
f_ptr();
object.print();
return 0;
}
END_OF_main
make
gdb main <<END_OF_gdb
b Derived::print
r
p derivedData
END_OF_gdb
-- System Information
Debian Release: testing/unstable
Architecture: i386
Kernel: Linux rincewind 2.4.20-686-smp #1 SMP Mon Jan 13 23:06:41 EST 2003 i686
Locale: LANG=C, LC_CTYPE=C
Versions of packages gdb depends on:
ii libc6 2.3.1-16 GNU C Library: Shared libraries an
ii libncurses5 5.3.20021109-2 Shared libraries for terminal hand
ii libreadline4 4.3-4 GNU readline and history libraries
--- End Message ---
--- Begin Message ---
I can't reproduce this with GDB 16.3:
--8<---------------cut here---------------start------------->8---
(gdb) b Derived::print() const
Breakpoint 1 at 0x22da: file main.cpp, line 35.
(gdb) r
Starting program: /root/main
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
print() at mylib.cpp:5
Breakpoint 1, Derived::print (this=0x7fffffffea90) at main.cpp:35
35 cout << get_base() << " " << derivedData << endl;
(gdb) p derivedData
$1 = 5
--8<---------------cut here---------------end--------------->8---
Closing the bug.
--
Sergio
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