term% cat index.txt SETJMP(2) System Calls Manual 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 interrupts en‐
countered 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 re‐
turned with value val. The invoker of setjmp must not itself have re‐
turned 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. Several macros
are defined in /$objtype/include/u.h that can be used to build jmp_bufs
by hand. The following code establishes a jmp_buf that may be called
by longjmp to begin execution in a function f with 1024 bytes of stack:
#include <u.h>
#include <libc.h>
jmp_buf label;
#define NSTACK 1024
char stack[NSTACK];
void
setlabel(void)
{
label[JMPBUFPC] = ((ulong)f+JMPBUFDPC);
/* -2 leaves room for old pc and new pc in frame */
label[JMPBUFSP] =
(ulong)(&stack[NSTACK-2*sizeof(ulong*)]);
}
SOURCE
/sys/src/libc/$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.
SETJMP(2)