none/tests/freebsd/swapcontext.c

   1 // obtained from https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.bpxbd00/rswctx.htm
   2
   3 #include <stdlib.h>
   4 #include <stdio.h>
   5 #include <ucontext.h>
   6 #include <errno.h>
   7
   8 #define STACK_SIZE 2097152+16384 /* large enough value for AMODE 64 */
   9
  10 ucontext_t fcontext,mcontext;
  11 int x = 0;
  12
  13 void func(int arg)
  14 {
  15    printf("function called with value %d\n",arg);
  16    x++;
  17    printf("function returning to main\n");
  18    setcontext(&mcontext);
  19 }
  20
  21 int main(void)
  22 {
  23    int  value = 1;
  24
  25    getcontext(&fcontext);
  26    if ((fcontext.uc_stack.ss_sp = (char *) malloc(STACK_SIZE)) != NULL)
  27    {
  28       fcontext.uc_stack.ss_size = STACK_SIZE;
  29       fcontext.uc_stack.ss_flags = 0;
  30       fcontext.uc_sigmask.__bits[3] = -1;
  31       errno = 0;
  32       makecontext(&fcontext,(void (*)(void))func,1,value);
  33       if (errno != 0)
  34       {
  35          perror("Error reported by makecontext()");
  36          return -1;    /* Error occurred exit */
  37       }
  38    }
  39    else
  40    {
  41       perror("not enough storage for stack");
  42       abort();
  43    }
  44
  45    printf("context has been built\n");
  46    swapcontext(&mcontext,&fcontext);
  47
  48    if (!x)
  49    {
  50      perror("incorrect return from swapcontext");
  51      abort();
  52    }
  53    else
  54    {
  55       printf("returned from function\n");
  56    }
  57    free(fcontext.uc_stack.ss_sp);
  58 }
  59
  60