PTHREAD...GETSTACK(3POSIX)

💖 PTHREAD...GETSTACK — the POSIX Programmer's Manual one, bestie 💖

okay so real talk: this page lives in the POSIX Programmer's Manual (yes, that one, the PTHREAD...GETSTACK(3POSIX) girlies know). Heads up though — the Linux implementation of this interface may differ, so if you're on Linux, go read the corresponding Linux manual page for the actual Linux behavior. Or maybe it's just not implemented on Linux at all. 🙈 Either way, vibe check your platform first.

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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 — they respectively get and set the thread creation stack attributes stackaddr and stacksize inside the attr object. Iconic. ✨

The stack attributes specify the area of storage that the created thread is gonna use for its stack. Here's the breakdown, no cap:

• the base (lowest addressable byte) of that storage shall be stackaddr
• the size of that storage shall be stacksize bytes
• stacksize shall be at least {PTHREAD_STACK_MIN}
• pthread_attr_setstack() may fail with [EINVAL] if stackaddr doesn't meet implementation-defined alignment requirements 👀
• all pages within the stack described by stackaddr and stacksize shall be both readable and writable by the thread

If you call pthread_attr_getstack() before the stackaddr attribute has been set, the behavior is unspecified. Not undefined, but like… don't. 🫠

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. Un. De. Fined. You have been warned, bestie. 💀

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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.

And pthread_attr_getstack() shall store the stack attribute values in stackaddr and stacksize if successful. Slay. 👑

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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. (i.e. the lore, not the rules ✨)

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🙈 EXAMPLES 🙈

None. That's it. That's the section. Nothing here. Moving on. 💀

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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. Very specific-stack-energy. 💅

So, it might seem like an application could detect stack overflow by providing a protected page outside the specified stack region — but nope, that 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 on some architectures — like the IA-64, hi bestie — ``overflow'' might mean that two separate stack pointers allocated within the region will overlap somewhere in the middle of the region. Not the vibe. 😭

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 gave it away. 🫶

And here's the tea: the specification of the stackaddr attribute presents several ambiguities that make portable use of these functions impossible. Fr fr. 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. Lowkey messy of the standard but okay. 🍓

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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. (recommended, bestie, not required — iykyk)

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⭐ FUTURE DIRECTIONS ⭐

None. Nothing's changing. Stable queen. 💜

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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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and that's the whole page, bestie 💖 this one came from IEEE/The Open Group, 2017, and it's PTHREAD...GETSTACK(3POSIX) — go forth and align your stacks responsibly ✨🦋🎀