1 .TH SETJMP 3
2 .SH NAME
3 setjmp, longjmp, notejmp \- non-local goto
4 .SH SYNOPSIS
5 .B #include <u.h>
6 .br
7 .B #include <libc.h>
8 .PP
9 .ta \w'\fLvoid 'u
10 .B
11 int	setjmp(jmp_buf env)
12 .PP
13 .B
14 void	longjmp(jmp_buf env, int val)
15 .PP
16 .B
17 void	notejmp(void *uregs, jmp_buf env, int val)
18 .SH DESCRIPTION
19 These routines are useful for dealing with errors
20 and interrupts encountered in
21 a low-level subroutine of a program.
22 .PP
23 .I Setjmp
24 saves its stack environment in
25 .I env
26 for later use by
27 .IR longjmp .
28 It returns value 0.
29 .PP
30 .I Longjmp
31 restores the environment saved by the last call of
32 .IR setjmp .
33 It then causes execution to
34 continue as if the call of
35 .I setjmp
36 had just returned with value
37 .IR val .
38 The invoker of
39 .I setjmp
40 must not itself have returned in the interim.
41 All accessible data have values as of the time
42 .I longjmp
43 was called.
44 .PP
45 .I Notejmp
46 is the same as
47 .I longjmp
48 except that it is to be called from within a note handler (see
49 .IR notify (3)).
50 The
51 .I uregs
52 argument should be the first argument passed to the note handler.
53 .PP
54 .I Setjmp
55 and
56 .I longjmp
57 can also be used to switch stacks.
58 Defined in
59 .B </$objtype/u.h>
60 are several macros that can be used to build
61 .B jmp_bufs
62 by hand.  The following code establishes a
63 .B jmp_buf
64 .i label
65 that may be called by
66 .I longjmp
67 to begin execution in a function
68 .BR f
69 with 1024 bytes of stack:
70 .IP
71 .EX
72 #include <u.h>
73 #include <libc.h>
74 
75 jmp_buf label;
76 #define NSTACK 1024
77 char stack[NSTACK];
78 
79 void
80 setlabel(void)
81 {
82 	label[JMPBUFPC] = ((ulong)f+JMPBUFDPC);
83 	/* -2 leaves room for old pc and new pc in frame */
84 	label[JMPBUFSP =
85 	        (ulong)(&stack[NSTACK-2*sizeof(ulong*)]);
86 }
87 .EE
88 .SH SOURCE
89 .B /usr/local/plan9/src/lib9/jmp.c
90 .SH SEE ALSO
91 .IR notify (3)
92 .SH BUGS
93 .PP
94 .I Notejmp
95 cannot recover from an address trap or bus error (page fault) on the 680x0
96 architectures.