call gettid witin glibc

Question

I am working in glibc and I need to get the id of the current thread. For this i use syscall(SYS_gettid); Issue is, i am forced to include bits/syscall.h instead of ideal case i.e sys/syscall.h.

sys/syscall.h internally calls bits/syscall.h but that is wrapped with #ifndef _LIBC macro. i.e

     #ifndef _LIBC
        /* The Linux kernel header file defines macros `__NR_<name>', but some
           programs expect the traditional form `SYS_<name>'.  So in building libc
           we scan the kernel's list and produce <bits/syscall.h> with macros for
           all the `SYS_' names.  */
       # include <bits/syscall.h>
    #endif

also bits/syscall.h states that "Never use bits/syscall.h directly; include sys/syscall.h instead."

Since _LIBC will be defined in my case as i am writing code directly in malloc.c, please suggest my how can i overcome this.

Thanks, Kapil

Answer 1

gettid() is a system call. As for as I know there is no glibc wrapper for gettid. You need to invoke gettid() using syscall(). The following code works for me.

#include <sys/syscall.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

int main()
{
    long tid;

    tid = syscall(SYS_gettid);
    printf("%ld\n", tid);
    return EXIT_SUCCESS;
}