Current uClibc-ng version incorrectly calculates clockid in pthread_getcpuclockid (at least for modern kernels). The simplest test program

#include <time.h>

#include <errno.h>

#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

int main()

{

    clockid_t clk;

    struct timespec ts;

    const int err = pthread_getcpuclockid(pthread_self(), &clk);

    if (err != 0) {

        errno = err;

        perror("pthread_getcpuclockid");

        return EXIT_FAILURE;

    }

    if (clock_gettime(clk, &ts) == -1) {

        perror("clock_gettime");

        return EXIT_FAILURE;

    }

    printf("Thread time is %lu.%06lu.\n",

           ts.tv_sec,

           ts.tv_nsec / 1000);

    return EXIT_SUCCESS;

}

fails with

clock_gettime: Invalid argument

Tested on Linux 3.4 / MIPS built with GCC 5.4.0.

Other implementations, for example musl, use a simple calculation

https://git.musl-libc.org/cgit/musl/tree/src/thread/pthread_getcpuclockid.c

Looks strange, but the official glibc repository

https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=nptl/pthread_getcpuclockid.c;hb=HEAD

has the same implementation as in uClibc-ng.

This fork https://github.com/lattera/glibc/blob/master/nptl/sysdeps/unix/sysv/linux/pthread_getcpuclockid.c

use more accurate approach relying on __NR_clock_getres (defined in the kernel since 2.6.24) with MAKE_THREAD_CPUCLOCK macro copied from the kernel (http://lxr.free-electrons.com/source/include/linux/posix-timers.h?v=2.6.24#L34, Linux 4.10 has the same one).

I propose an intermediate solution: use MAKE_THREAD_CPUCLOCK like computation of clockid when __NR_clock_getres defined and do a fallback to an older implementation when not.