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 void *__vdsosym(const char *, const char *);
  10
  11 static void *volatile vdso_func;
  12
  13 typedef long (*getcpu_f)(unsigned *, unsigned *, void *);
  14
  15 static long getcpu_init(unsigned *cpu, unsigned *node, void *unused)
  16 {
  17         void *p = __vdsosym(VDSO_GETCPU_VER, VDSO_GETCPU_SYM);
  18         getcpu_f f = (getcpu_f)p;
  19         a_cas_p(&vdso_func, (void *)getcpu_init, p);
  20         return f ? f(cpu, node, unused) : -ENOSYS;
  21 }
  22
  23 static void *volatile vdso_func = (void *)getcpu_init;
  24
  25 #endif
  26
  27 int sched_getcpu(void)
  28 {
  29         int r;
  30         unsigned cpu;
  31
  32 #ifdef VDSO_GETCPU_SYM
  33         getcpu_f f = (getcpu_f)vdso_func;
  34         if (f) {
  35                 r = f(&cpu, 0, 0);
  36                 if (!r) return cpu;
  37                 if (r != -ENOSYS) return __syscall_ret(r);
  38         }
  39 #endif
  40
  41         r = __syscall(SYS_getcpu, &cpu, 0, 0);
  42         if (!r) return cpu;
  43         return __syscall_ret(r);
  44 }