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.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.

Several macros are defined in

.B /$objtype/include/u.h

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.