src/cf/ucontext.m4

   1 dnl Test getcontext() and makecontext() to ensure that we are able to
   2 dnl copy the current user context, modify it with our own private stack
   3 dnl and return to the original user context.
   4 dnl
   5 AC_DEFUN([OPENAFS_WORKING_UCONTEXT],[
   6   AC_MSG_CHECKING([if user context manipulation is complete])
   7   AC_RUN_IFELSE(
   8     [AC_LANG_SOURCE(
   9       [[
  10 #include <stdio.h>
  11 #include <stdlib.h>
  12 #ifdef HAVE_UCONTEXT_H
  13 #include <ucontext.h>
  14 #endif
  15
  16 #define STACK_SIZE 16384
  17
  18 static ucontext_t main_context, thread_context;
  19 static char *alt_stack;
  20
  21 static void
  22 thread(void)
  23 {
  24         unsigned long stack_ptr;
  25         unsigned long offset;
  26
  27         offset = (unsigned long) &stack_ptr - (unsigned long) alt_stack;
  28         if (offset > STACK_SIZE)
  29                 exit(EXIT_FAILURE);
  30         swapcontext(&thread_context, &main_context);
  31         /* should never get here */
  32         exit(EXIT_FAILURE);
  33 }
  34
  35 int
  36 main(int argc, char **argv)
  37 {
  38         if (getcontext(&thread_context) == -1)
  39                 exit(EXIT_FAILURE);
  40         alt_stack = malloc(STACK_SIZE);
  41         if (!alt_stack)
  42                 exit(EXIT_FAILURE);
  43         thread_context.uc_stack.ss_sp = alt_stack;
  44         thread_context.uc_stack.ss_size = STACK_SIZE;
  45         makecontext(&thread_context, thread, 0);
  46
  47         if (swapcontext(&main_context, &thread_context) == -1)
  48                 exit(EXIT_FAILURE);
  49
  50         free(alt_stack);
  51         exit(EXIT_SUCCESS);
  52 }
  53       ]])],
  54       [AC_MSG_RESULT(yes)
  55        AC_DEFINE(HAVE_WORKING_SWAPCONTEXT, 1,
  56          user context manipulation is complete)],
  57       [AC_MSG_RESULT(no)],
  58       [])])