_LONGJMP(3P)

💖 _LONGJMP(3P) — POSIX Programmer's Manual 💖

okay bestie so we're in the POSIX Programmer's Manual rn, that's the vibe. quick heads up before we even start, no cap:

🫶 PROLOG 🫶

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

literally read that twice. Linux might do its own thing, or not have it at all. don't come for me, come for the Linux man page. 💀

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✨ NAME ✨

_longjmp, _setjmp — non-local goto

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🌸 SYNOPSIS 🌸

#include <setjmp.h>

void _longjmp(jmp_buf env, int val);
int _setjmp(jmp_buf env);

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🦋 DESCRIPTION 🦋

So _longjmp() and _setjmp() are equivalent to longjmp() and setjmp(), respectively — but with one extra restriction, and it's the whole personality: _longjmp() and _setjmp() shall not manipulate the signal mask. like, they just don't touch it. iconic of them honestly.

And now the scary part, so listen up 🫶 — if _longjmp() is called even though env was never initialized by a call to _setjmp(), or when the last such call was in a function that has since returned, the results are undefined. undefined. as in, we don't know what happens. nobody knows. chaos. 😭

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💜 RETURN VALUE 💜

Refer to longjmp() and setjmp().

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🎀 ERRORS 🎀

No errors are defined.

The following sections are informative.

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🍓 EXAMPLES 🍓

None.

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👑 APPLICATION USAGE 👑

okay this is the part where we get real. if _longjmp() is executed and the environment in which _setjmp() was executed no longer exists, errors can occur. and what counts as "the environment no longer exists"? the conditions include:

• exiting the function that contains the _setjmp() call, and
• exiting an inner block with temporary storage.

This condition might not be detectable, in which case the _longjmp() occurs and, if the environment no longer exists, the contents of the temporary storage of an inner block are unpredictable. This condition might also cause unexpected process termination. If the function has returned, the results are undefined.

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and it gets worse bestie, sorry. passing longjmp() a pointer to a buffer not created by setjmp(), passing _longjmp() a pointer to a buffer not created by _setjmp(), passing siglongjmp() a pointer to a buffer not created by sigsetjmp(), or passing any of these three functions a buffer that has been modified by the user — any of those can cause all the problems listed above, and more. and more!! the audacity.

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The _longjmp() and _setjmp() functions are included to support programs written to historical system interfaces. New applications should use siglongjmp() and sigsetjmp() respectively. that's the group chat advice, take it. 💅

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🌈 RATIONALE 🌈

None.

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⭐ FUTURE DIRECTIONS ⭐

The _longjmp() and _setjmp() functions may be removed in a future version. so like… don't build your whole life on them, yk?

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🔥 SEE ALSO 🔥

• longjmp()
• setjmp()
• siglongjmp()
• sigsetjmp()

The Base Definitions volume of POSIX.1‐2017, <setjmp.h>

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🧚 COPYRIGHT 🧚

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie 💖 this one came to you courtesy of IEEE/The Open Group, 2017, page _LONGJMP(3P) — go forth and do NOT call _longjmp() on a stale env, i am begging 🙈