New subject: [PATCH] pthread_getcpuclockid.c: fix clockid calculation

25 Apr 2017


      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_getcpucl...
has the same implementation as in uClibc-ng.
This fork
https://github.com/lattera/glibc/blob/master/nptl/sysdeps/unix/sysv/linux/pt...
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#L...,
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.