TH SETJMP 2
SH NAME
setjmp, longjmp, notejmp \- non-local goto
SH SYNOPSIS
B #include <u.h>
br
B #include <libc.h>
PP
ta \w'\fLvoid 'u
B
int     setjmp(jmp_buf env)
PP
B
void    longjmp(jmp_buf env, int val)
PP
B
void    notejmp(void *uregs, jmp_buf env, int val)
SH DESCRIPTION
These routines are useful for dealing with errors
and interrupts encountered in
a low-level subroutine of a program.
PP
I Setjmp
saves its stack environment in
I env
for later use by
IR longjmp .
It returns value 0.
PP
I Longjmp
restores the environment saved by the last call of
IR setjmp .
It then causes execution to
continue as if the call of
I setjmp
had just returned with value
IR val .
The invoker of
I setjmp
must not itself have returned in the interim.
All accessible data have values as of the time
I longjmp
was called.
PP
I Notejmp
is the same as
I longjmp
except that it is to be called from within a note handler (see
IR notify (2)).
The
I uregs
argument should be the first argument passed to the note handler.
PP
I Setjmp
and
I longjmp
can also be used to switch stacks.
Defined in
B </$objtype/u.h>
are several macros that can be used to build
B jmp_bufs
by hand.  The following code establishes a
B jmp_buf
i label
that may be called by
I longjmp
to begin execution in a function
BR f
with 1024 bytes of stack:
IP
EX
#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*)]);
}
EE
SH SOURCE
B /sys/src/libc/$objtype/setjmp.s
br
B /sys/src/libc/$objtype/notejmp.c
SH SEE ALSO
IR notify (2)
SH BUGS
PP
I Notejmp
cannot recover from an address trap or bus error (page fault) on the 680x0
architectures.