UCONTEXT(2)

🦋 ucontext(2) — user context 🦋

okay so bestie, this is the ucontext page from the System Calls Manual, section 2, and it is literally all about a thread’s user context ✨

💖 NAME 💖

ucontext — user context. concise, iconic, periodt 💅

🎀 SYNOPSIS 🎀

#include <ucontext.h>

_UC_MACHINE_SP(&uc);

_UC_MACHINE_FP(&uc);

_UC_MACHINE_PC(&uc);

_UC_MACHINE_INTRV(&uc);

_UC_MACHINE_SET_PC(&uc);

🌸 DESCRIPTION 🌸

The ucontext_t is a structure type, and it is used to describe the context of a thread of control within the execution of a process. A thread’s context includes its stack, saved registers, and list of blocked signals. no cap, that is the whole vibe 🫶

The ucontext_t structure includes the following members:

ucontext_t *uc_link
sigset_t    uc_sigmask
stack_t     uc_stack
mcontext_t  uc_mcontext

• uc_link — points to the context that will be resumed after the function specified when modifying a context using makecontext(3) has returned. If uc_link is a NULL pointer, then the context is the main context, and the process will exit with an exit status of 0 upon return. main character energy, honestly 👑
• uc_sigmask — this is the set of signals that are blocked when the context is activated. further information can be found in sigprocmask(2). signal blocking, but make it fashion 💅
• uc_stack — defines the stack used by the context. further information can be found in sigaltstack(2). stack behavior, very demure, very mindful 🎀
• uc_mcontext — defines the machine state associated with the context; it may consist of general registers, floating point registers and other machine-specific information. its description is beyond the scope of this manual page; portable applications should not access this structure member. like, do not touch, bestie 🙈

The following auxiliary macros are available to access some of that machine-specific information:

• _UC_MACHINE_SP() — read stack pointer,
• _UC_MACHINE_FP() — read frame pointer (base pointer),
• _UC_MACHINE_PC() — read program counter,
• _UC_MACHINE_INTRV() — read integer return value,
• _UC_MACHINE_SET_PC() — write program counter.

The frame pointer macro does not guarantee to retrieve a reliable value and should not be used in a code unless no other debugging format is easily accessible. a compiler might optimize the frame pointer register in a function, reusing it as a general purpose register storage (-fomit-frame-pointer) or emit function prologues only before parts that need them (-fshrink-wrap). so like, it’s giving “use at your own risk,” and the risk is real 💀

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🔥 SEE ALSO 🔥

_exit(2), getcontext(2), setcontext(2), sigaltstack(2), sigprocmask(2), makecontext(3), swapcontext(3)

👑 STANDARDS 👑

The ucontext_t type conforms to X/Open System Interfaces and Headers Issue 5 (“XSH5”) and IEEE Std 1003.1-2001 (“POSIX.1”). The IEEE Std 1003.1-2008 (“POSIX.1”) revision removed the ucontext_t from the specification. so yes, it was iconic, then it got removed from the spec — we love a complicated legacy 😭

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this page is from Debian, dated February 25, 2018 — mwah, slay 💋✨