In GDB, what is the proper way to call C++ functions inside namespaces or classes in non-debug binaries?

Question

GDB's call command normally works great for calling functions, as long as the symbols are present. But if the function is in a namespace or a class, suddenly it won't work unless it was compiled with debugging information.

For example, let's say I have this program:

#include <iostream>

namespace ns {
    void test()
    {
        std::cout << "ns::test" << std::endl;
    }
}

struct cl {
    static void test()
    {
        std::cout << "cl::test" << std::endl;
    }
};

void func()
{
    std::cout << "func" << std::endl;
}

int main()
{
    ns::test();
    cl::test();
    func();
    return 0;
}

I saved that as test.cpp, compiled it with g++ test.cpp -o test, then started it inside GDB:

$ gdb test
GNU gdb (GDB) 11.1
[...]
Reading symbols from test...
(No debugging symbols found in test)
(gdb) start

Calling func from GDB works as expected:

(gdb) call (void)func()
func

The others, however, do not:

(gdb) call (void)ns::test()
No symbol "ns" in current context.
(gdb) call (void)cl::test()
No symbol "cl" in current context.

It works fine if it was compiled with -ggdb, but that's not usually an option if the source code is unavailable.

It's worth pointing out that GDB is aware of these functions and their addresses:

(gdb) info functions
...
0x0000000000001169  ns::test()
0x000000000000119b  func()
0x000000000000124e  cl::test()
...
(gdb) info symbol 0x1169
ns::test() in section .text
(gdb) break cl::test()
Breakpoint 1 at 0x1252

Those names will also autocomplete if I press Tab, even in a call command, meaning in that case it will autocomplete to something that doesn't work.

In addition, calling those functions works fine if I use their raw names:

(gdb) call (void)_ZN2ns4testEv()
ns::test
(gdb) call (void)_ZN2cl4testEv()
cl::test

So what's the deal here? Is this a bug in GDB, or is there some kind of special syntax I'm unaware of?

Newbill

Try quoting the whole thing so GDB doesn't try to search for the nonexistent ns symbol. call (void)'ns::test'(). Also, GDB willl use the C calling convention, and that's OK in this case but not generally. – Vasilek

@MarkPlotnick That worked; thanks a lot! Can you please post this as an answer so I can accept it? – Newbill

Answer 1

Your C++ compiler kindly put ns::test into the symbol table. All we need to do is prevent GDB's expression evaluator from trying to look up the non-existent symbol ns. To do this, put the entire function name in single quotes.

(gdb) call (void)'ns::test'()
ns::test

Vasilek