I really don’t get this, I have the following C++ program:

#include <cstring>
#include <stdexcept>

#include <fcntl.h>
#include <linux/if.h>
#include <linux/if_tun.h>
#include <sys/ioctl.h>
#include <unistd.h>


int main()
{
  int fd;
  if ((fd = ::open("/dev/net/tun", O_RDWR|O_CLOEXEC)) == -1)
    throw std::runtime_error("failed to open /dev/net/tun");

  ifreq ifr {};
  ifr.ifr_flags = IFF_TUN | IFF_NO_PI;
  std::strncpy(ifr.ifr_name, "tunnel", IFNAMSIZ);

  if (::ioctl(fd, TUNSETIFF, &ifr) == -1)
    throw std::runtime_error("failed to create TUN interface");
}

The program is built as follows:

g++ -g -O0 main.cc -o main
sudo setcap cap_net_admin=ep main

I want to now use gdb to inspect the arguments passed to the TUNSETIFF ioctl (in this case I know that they are of course but really I want to figure this out for another program where I don’t):

gdb ./main
(gdb) b ioctl
Breakpoint 1 at 0x1130|
(gdb) r
Starting program: ./main 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Breakpoint 1, __GI___ioctl (fd=3, request=1074025674) at ../sysdeps/unix/sysv/linux/ioctl.c:26
26      ../sysdeps/unix/sysv/linux/ioctl.c: No such file or directory.
(gdb) p *request
Cannot access memory at address 0x400454ca

So that’s not very helpful, how to I break on the libc ::ioctl call instead of whatever __GI___ioctl is?