src/sched/sched_getcpu.c

   1 #define _GNU_SOURCE
   2 #include <errno.h>
   3 #include <sched.h>
   4 #include "syscall.h"
   5 #include "atomic.h"
   6
   7 #ifdef VDSO_GETCPU_SYM
   8
   9 static void *volatile vdso_func;
  10
  11 typedef long (*getcpu_f)(unsigned *, unsigned *, void *);
  12
  13 static long getcpu_init(unsigned *cpu, unsigned *node, void *unused)
  14 {
  15         void *p = __vdsosym(VDSO_GETCPU_VER, VDSO_GETCPU_SYM);
  16         getcpu_f f = (getcpu_f)p;
  17         a_cas_p(&vdso_func, (void *)getcpu_init, p);
  18         return f ? f(cpu, node, unused) : -ENOSYS;
  19 }
  20
  21 static void *volatile vdso_func = (void *)getcpu_init;
  22
  23 #endif
  24
  25 int sched_getcpu(void)
  26 {
  27         int r;
  28         unsigned cpu;
  29
  30 #ifdef VDSO_GETCPU_SYM
  31         getcpu_f f = (getcpu_f)vdso_func;
  32         if (f) {
  33                 r = f(&cpu, 0, 0);
  34                 if (!r) return cpu;
  35                 if (r != -ENOSYS) return __syscall_ret(r);
  36         }
  37 #endif
  38
  39         r = __syscall(SYS_getcpu, &cpu, 0, 0);
  40         if (!r) return cpu;
  41         return __syscall_ret(r);
  42 }