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Man Pages
UCONTEXT(3) FreeBSD Library Functions Manual UCONTEXT(3)

ucontext
user thread context

Standard C Library (libc, -lc)

#include <ucontext.h>

The ucontext_t type is a structure type suitable for holding the context for a user thread of execution. A thread's context includes its stack, saved registers, and list of blocked signals.

The ucontext_t structure contains at least these fields:

ucontext_t *uc_link
context to assume when this one returns
sigset_t uc_sigmask
signals being blocked
stack_t uc_stack
stack area
mcontext_t uc_mcontext
saved registers

The uc_link field points to the context to resume when this context's entry point function returns. If uc_link is equal to NULL, then the process exits when this context returns.

The uc_mcontext field is machine-dependent and should be treated as opaque by portable applications.

The following functions are defined to manipulate ucontext_t structures:

  • int getcontext(ucontext_t *);
  • ucontext_t * getcontextx(void);
  • int setcontext(const ucontext_t *);
  • void makecontext(ucontext_t *, void (*)(void), int, ...);
  • int swapcontext(ucontext_t *, const ucontext_t *);

sigaltstack(2), getcontext(3), getcontextx(3), makecontext(3)

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.
March 23, 2020 FreeBSD 13.1-RELEASE

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