pthread_attr_setstack(3)

💖 pthread_attr_setstack — bestie, we're doing manual stacks now 💖

okay so real talk: this is a page from the Library Functions Manual (yes, section 3, the library functions girlies), and it's about two little functions that let you control exactly where a thread's stack lives. It's giving "I have very specific needs" energy. Let's go. 🫶

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✨ NAME ✨

pthread_attr_setstack, pthread_attr_getstack — set/get stack attributes in thread attributes object

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🌸 LIBRARY 🌸

POSIX threads library (libpthread, -lpthread)

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🎀 SYNOPSIS 🎀

#include <pthread.h>

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

🦋 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

• pthread_attr_getstack(), pthread_attr_setstack():
  • _POSIX_C_SOURCE >= 200112L

lowkey important: if you don't define that macro, glibc is gonna act like it doesn't know her. 💅

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💜 DESCRIPTION 💜

So pthread_attr_setstack() sets the stack address and stack size attributes of the thread attributes object that attr points at — setting them to whatever you passed in stackaddr and stacksize, respectively. And what do those attributes even mean? They specify the location and size of the stack that a thread created with the attributes object attr should use. Like, you're hand-picking the real estate. 🏠

stackaddr should point to the lowest addressable byte of a buffer of stacksize bytes that was allocated by you, the caller. And the pages of that allocated buffer should be both readable and writable. No read-only zones, bestie, she needs full access. ✨

And pthread_attr_getstack()? She's the reverse uno card: she returns the stack address and stack size attributes of the thread attributes object referred to by attr, dropping them into the buffers pointed to by stackaddr and stacksize, respectively. 💫

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🔥 RETURN VALUE 🔥

On success, these functions return 0; on error, they return a nonzero error number. That's it, that's the whole vibe.

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💀 ERRORS 💀

pthread_attr_setstack() can fail with the following error:

• EINVAL — stacksize is less than PTHREAD_STACK_MIN (16384) bytes. On some systems, this error may also occur if stackaddr or stackaddr + stacksize is not suitably aligned.

POSIX.1 also documents an EACCES error if the stack area described by stackaddr and stacksize is not both readable and writable by the caller.

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🌈 ATTRIBUTES 🌈

For an explanation of the terms used in this section, see attributes(7).

• Interface: pthread_attr_setstack(), pthread_attr_getstack()
  • Attribute: Thread safety
  • Value: MT-Safe

yes bestie, they're MT-Safe, we love a safe queen 👑

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⭐ STANDARDS ⭐

POSIX.1-2008.

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🧚 HISTORY 🧚

glibc 2.2. POSIX.1-2001.

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🍓 NOTES 🍓

These functions are provided for applications that must ensure that a thread's stack is placed in a particular location. But for most applications, this is not necessary, and honestly the use of these functions should be avoided. Like, fr fr, don't unless you must. (Use pthread_attr_setstacksize(3) if an application simply requires a stack size other than the default — that's the chill version.)

When an application employs pthread_attr_setstack(), it takes over the responsibility of allocating the stack. Any guard size value that was set using pthread_attr_setguardsize(3) is ignored. If deemed necessary, it is the application's responsibility to allocate a guard area (one or more pages protected against reading and writing) to handle the possibility of stack overflow. So like… you wanted to be in charge? You're in charge now. 😭

The address specified in stackaddr should be suitably aligned: for full portability, align it on a page boundary (sysconf(_SC_PAGESIZE)). posix_memalign(3) may be useful for allocation. Probably, stacksize should also be a multiple of the system page size. Alignment is the moment, no cap. 💅

🚨 okay this one matters: If attr is used to create multiple threads, then the caller must change the stack address attribute between calls to pthread_create(3); otherwise, the threads will attempt to use the same memory area for their stacks, and chaos will ensue. Not the cute kind of chaos. The crashy kind. 💀

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🙈 EXAMPLES 🙈

See pthread_attr_init(3). She's got the receipts. ✨

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👑 SEE ALSO 👑

mmap(2), mprotect(2), posix_memalign(3), pthread_attr_init(3), pthread_attr_setguardsize(3), pthread_attr_setstackaddr(3), pthread_attr_setstacksize(3), pthread_create(3), pthreads(7)

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and that's the whole page, bestie!! this one's from Linux man-pages 6.20, dated 2025-06-28, and it's the pthread_attr_setstack(3) page 💖 go forth, allocate responsibly, and remember: guard pages are self-care 🎀✨🌸