CODEWITHSUNDEEP
glibc
hellow
hellow

Reputation: 13440

Using linux syscall with older glibc

I want to use the timerfd in a embedded device solution which runs a 2.6.39 kernel, but the cross compiler uses a too old glibc (2.5). Timerfd exists since 2.6.25, but only since glibc 2.8

When i try to use the header file from a newer glibc, the compiler complains about not finding the extern timerfd_create (undefined reference to 'timerfd_create'), but I can't find the implementation anywhere in the glibc.

My question now is, how can I use the timerfd, regardless of the old glibc version? Do I have to invoke the syscall manually? If yes, how do I do so?

Upvotes: 0

Views: 540

Answers (1)

Employed Russian
Employed Russian

Reputation: 213754

I can't find the implementation anywhere in the glibc.

Here is trick to finding it: with libc6-dbg installed:

gdb -q  /lib/x86_64-linux-gnu/libc.so.6
(gdb) list timerfd_create
61  ../sysdeps/unix/syscall-template.S: No such file or directory.

This tells you that the implementation is simply to pass arguments directly to the kernel via system call.

Your implementation can then be:

#include <unistd.h>
#include <syscall.h>

#ifndef __NR_timerfd_create
#define __NR_timerfd_create 283
int timerfd_create(int clockid, int flags)
{
  return syscall(__NR_timerfd_create, clockid, flags);
}
#endif

Upvotes: 1

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