1LIBUNWIND-SETJMP(3) Programming Library LIBUNWIND-SETJMP(3)
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6 libunwind-setjmp -- libunwind-based non-local gotos
7
9 #include <setjmp.h>
10 int setjmp(jmp_buf env);
12 void longjmp(jmp_buf env, int val);
13 int _setjmp(jmp_buf env);
14 void _longjmp(jmp_buf env, int val);
15 int setjmp(sigjmp_buf env, int savemask);
16 void siglongjmp(sigjmp_buf env, int val);
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19 The unwind-setjmp library offers a libunwind-based implementation of
20 non-local gotos. This implementation is intended to be a drop-in
21 replacement for the normal, system-provided routines of the same name.
22 The main advantage of using the unwind-setjmp library is that setting
23 up a non-local goto via one of the setjmp() routines is very fast. Typ‐
24 ically, just 2 or 3 words need to be saved in the jump-buffer (plus one
25 call to sigprocmask(2), in the case of sigsetjmp). On the other hand,
26 executing a non-local goto by calling one of the longjmp() routines
27 tends to be much slower than with the system-provided routines. In
28 fact, the time spent on a longjmp() will be proportional to the number
29 of call frames that exist between the points where setjmp() and
30 longjmp() were called. For this reason, the unwind-setjmp library is
31 beneficial primarily in applications that frequently call setjmp() but
32 only rarely call longjmp().
33
35 * The correct operation of this library depends on the presence of
36 correct unwind information. On newer platforms, this is rarely
37 an issue. On older platforms, care needs to be taken to ensure
38 that each of the functions whose stack frames may have to be
39 unwound during a longjmp() have correct unwind information (on
40 those platforms, there is usually a compiler-switch, such as
41 -funwind-tables, to request the generation of unwind informa‐
42 tion).
43 * The contents of jmp_buf and sigjmp_buf as setup and used by
45 these routines is completely different from the ones used by the
46 system-provided routines. Thus, a jump-buffer created by the
47 libunwind-based setjmp()/_setjmp may only be used in a call to
48 the libunwind-based longjmp()/_longjmp(). The analogous applies
49 for sigjmp_buf with sigsetjmp() and siglongjmp().
50
52 -lunwind-setjmp
53 The library an application should be linked against to ensure
54 it uses the libunwind-based non-local goto routines.
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57 libunwind(3), setjmp(3), longjmp(3), _setjmp(3), _longjmp(3),
58 sigsetjmp(3), siglongjmp(3)
59
61 David Mosberger-Tang
62 Hewlett-Packard Labs
63 Palo-Alto, CA 94304
64 Email: davidm@hpl.hp.com
65 WWW: http://www.hpl.hp.com/research/linux/libunwind/.
66Programming Library 05 August 2004 LIBUNWIND-SETJMP(3)