SETJMP(2)                                               SETJMP(2)

     NAME
          setjmp, longjmp, notejmp - non-local goto

     SYNOPSIS
          #include <u.h>
          #include <libc.h>

          int  setjmp(jmp_buf env)

          void longjmp(jmp_buf env, int val)

          void notejmp(void *uregs, jmp_buf env, int val)

     DESCRIPTION
          These routines are useful for dealing with errors and inter-
          rupts encountered in a low-level subroutine of a program.

          Setjmp saves its stack environment in env for later use by
          longjmp. It returns value 0.

          Longjmp restores the environment saved by the last call of
          setjmp. It then causes execution to continue as if the call
          of setjmp had just returned with value val. The invoker of
          setjmp must not itself have returned in the interim.  All
          accessible data have values as of the time longjmp was
          called.

          Notejmp is the same as longjmp except that it is to be
          called from within a note handler (see notify(2)). The uregs
          argument should be the first argument passed to the note
          handler.

          Setjmp and longjmp can also be used to switch stacks.  Sev-
          eral macros are defined in /$objtype/include/u.h that can be
          used to build jmp_bufs by hand.  The following code estab-
          lishes a jmp_buf that may be called by longjmp to begin exe-
          cution in a function f with 1024 bytes of stack:

               #include <u.h>
               #include <libc.h>

               jmp_buf label;
               #define NSTACK 1024
               char stack[NSTACK];

               void
               setlabel(void)
               {
                    label[JMPBUFPC] = ((ulong)f+JMPBUFDPC);
                    /* -2 leaves room for old pc and new pc in frame */

     Page 1                       Plan 9            (printed 12/21/24)

     SETJMP(2)                                               SETJMP(2)

                    label[JMPBUFSP] =
                            (ulong)(&stack[NSTACK-2*sizeof(ulong*)]);
               }

     SOURCE
          /sys/src/libc/$objtype/setjmp.s
          /sys/src/libc/$objtype/notejmp.c

     SEE ALSO
          notify(2)

     BUGS
          Notejmp cannot recover from an address trap or bus error
          (page fault) on the 680x0 architectures.

     Page 2                       Plan 9            (printed 12/21/24)