PR_SET_MM_ARG_START(2const)

💅 PR_SET_MM_ARG_START(2const) ✨

okay bestie so this is a Linux man page, from the 2const crew — it's all about PR_SET_MM_ARG_START, PR_SET_MM_ARG_END, PR_SET_MM_ENV_START, and PR_SET_MM_ENV_END, and what they do is modify kernel memory map descriptor fields. yes that's the whole vibe. we're messing with where the kernel thinks your argv and environ live. iconic behavior, honestly 🫶

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📚 LIBRARY

Standard C library (libc, -lc). the humble little libc, carrying all of us on her back fr fr 💖

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✨ SYNOPSIS

#include <linux/prctl.h>  /* Definition of PR_* constants */
#include <sys/prctl.h>

int prctl(PR_SET_MM, PR_SET_MM_ARG_START, unsigned long addr, 0L, 0L);
int prctl(PR_SET_MM, PR_SET_MM_ARG_END, unsigned long addr, 0L, 0L);
int prctl(PR_SET_MM, PR_SET_MM_ENV_START, unsigned long addr, 0L, 0L);
int prctl(PR_SET_MM, PR_SET_MM_ENV_END, unsigned long addr, 0L, 0L);

like. look at her. four calls, one addr, and three lil 0Ls tagging along for moral support 🌸

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🎀 DESCRIPTION

okay so each of these four constants is a different boundary setter, and they're all lowkey just drawing invisible lines around your process memory 💫

• PR_SET_MM_ARG_START — sets the address above which the program command line is placed.
• PR_SET_MM_ARG_END — sets the address below which the program command line is placed.
• PR_SET_MM_ENV_START — sets the address above which the program environment is placed.
• PR_SET_MM_ENV_END — sets the address below which the program environment is placed.

and now the important part, bestie, do not skip this 👀

the addr you pass with these calls should belong to a process stack area. so the corresponding memory area has to be readable, writable, and — depending on how your kernel was configured — have the MAP_GROWSDOWN attribute set (go peek at mmap(2)).

so like. it's giving "yes you can move the boundary but the memory has to actually be eligible" 😭 so valid.

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🔥 RETURN VALUE

slay and simple:

• on success, 0 is returned ✨
• on error, -1 is returned, and errno is set to tell you what went wrong 💀

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💀 ERRORS

• EINVAL — addr is greater than TASK_SIZE (that's the limit on the size of the user address space for this architecture).

that's it, that's the whole error list. one (1) singular error and she ate 👑

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🌈 STANDARDS

Linux. periodt.

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🦋 HISTORY

Linux 3.5. vintage, but in a cute way 💜

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👀 SEE ALSO

• prctl(2)
• PR_SET_MM(2const)

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and that's the whole page, bestie!! go forth and boundary-set responsibly 🫶

this was PR_SET_MM_ARG_START(2const) from Linux man-pages 6.20, dated 2026-02-08 — mwah, tysm for reading, ily, bye 💖✨🎀