PTHREAD_ATTR_GETSTACK(3P)

💖 PTHREAD_ATTR_GETSTACK(3P) 💖

okay bestie, welcome to the POSIX Programmer's Manual ✨ this one's from the POSIX side of town, so heads up: the Linux implementation of this interface may differ (peep the matching Linux manual page for the Linux tea 🫖), or honestly it might just not be implemented on Linux at all. no cap. 💀

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🌸 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.

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✨ NAME ✨

pthread_attr_getstack, pthread_attr_setstack — get and set stack attributes 💅

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🎀 SYNOPSIS 🎀

#include <pthread.h>

int pthread_attr_getstack(const pthread_attr_t *restrict attr,
    void **restrict stackaddr, size_t *restrict stacksize);
int pthread_attr_setstack(pthread_attr_t *attr, void *stackaddr,
    size_t stacksize);

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🦋 DESCRIPTION 🦋

So pthread_attr_getstack() and pthread_attr_setstack() are the get-and-set duo, and what they're doing is respectively getting and setting the thread creation stack attributes stackaddr and stacksize inside the attr object. main character behavior fr fr 👑

The stack attributes specify the area of storage to be used for the created thread's stack. The base (lowest addressable byte) of that storage shall be stackaddr, and the size of the storage shall be stacksize bytes. And stacksize shall be at least {PTHREAD_STACK_MIN} — that's the floor, babe, don't go under it. The pthread_attr_setstack() function may fail with [EINVAL] if stackaddr does not meet implementation-defined alignment requirements. Also: all pages within the stack described by stackaddr and stacksize shall be both readable and writable by the thread. both. not one. both. 🫶

If the pthread_attr_getstack() function is called before the stackaddr attribute has been set, the behavior is unspecified. like, nobody knows what happens. chaos. 🙈

And the behavior is undefined if the value specified by the attr argument to pthread_attr_getstack() or pthread_attr_setstack() does not refer to an initialized thread attributes object. undefined behavior is not a vibe, bestie, please pass it a real initialized object. 💀

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💜 RETURN VALUE 💜

Upon successful completion, these functions shall return a value of 0; otherwise, an error number shall be returned to indicate the error.

The pthread_attr_getstack() function shall store the stack attribute values in stackaddr and stacksize if successful. 🎁

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🔥 ERRORS 🔥

The pthread_attr_setstack() function shall fail if:

• EINVAL — The value of stacksize is less than {PTHREAD_STACK_MIN} or exceeds an implementation-defined limit.

The pthread_attr_setstack() function may fail if:

• EINVAL — The value of stackaddr does not have proper alignment to be used as a stack, or ((char *)stackaddr + stacksize) lacks proper alignment.
• EACCES — The stack page(s) described by stackaddr and stacksize are not both readable and writable by the thread.

These functions shall not return an error code of [EINTR]. periodt. 💅

The following sections are informative.

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🌈 EXAMPLES 🌈

None. 😭 (yeah, nothing, iconic of them honestly)

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⭐ APPLICATION USAGE ⭐

These functions are appropriate for use by applications in an environment where the stack for a thread must be placed in some particular region of memory. iykyk 🧚

Now here's the thing — while it might seem that an application could detect stack overflow by providing a protected page outside the specified stack region, this cannot be done portably. Implementations are free to place the thread's initial stack pointer anywhere within the specified region to accommodate the machine's stack pointer behavior and allocation requirements. And furthermore, on some architectures, such as the IA‐64, ``overflow'' might mean that two separate stack pointers allocated within the region will overlap somewhere in the middle of the region. so like, your clever little guard page trick? not portable. sorry bestie. 💀

After a successful call to pthread_attr_setstack(), the storage area specified by the stackaddr parameter is under the control of the implementation, as described in Section 2.9.8, Use of Application-Managed Thread Stacks. it's not yours anymore, you handed it over 🫡

The specification of the stackaddr attribute presents several ambiguities that make portable use of these functions impossible. For example, the standard allows implementations to impose arbitrary alignment requirements on stackaddr. Applications cannot assume that a buffer obtained from malloc() is suitably aligned. And note: although the stacksize value passed to pthread_attr_setstack() must satisfy alignment requirements, the same is not true for pthread_attr_setstacksize() — where the implementation must increase the specified size if necessary to achieve the proper alignment. different rules for different functions, keep up 🎀

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💅 RATIONALE 💅

If an implementation detects that the value specified by the attr argument to pthread_attr_getstack() or pthread_attr_setstack() does not refer to an initialized thread attributes object, it is recommended that the function should fail and report an [EINVAL] error.

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🍓 FUTURE DIRECTIONS 🍓

None. (the future is... nothing?? okay then 😌)

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👑 SEE ALSO 👑

• pthread_attr_destroy()
• pthread_attr_getdetachstate()
• pthread_attr_getstacksize()
• pthread_create()

The Base Definitions volume of POSIX.1‐2017, <limits.h>, <pthread.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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okay that's the whole page bestie, you ate that 🫶 this was IEEE/The Open Group, 2017, and the page name is PTHREAD_ATTR_GETSTACK(3P) — go forth and set your stacks responsibly, mwah 💋✨