NAME

ucontext — user context

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 which 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.

The ucontext_t structure includes the following members:

ucontext_t *uc_link
sigset_t    uc_sigmask
stack_t     uc_stack
mcontext_t  uc_mcontext

The uc_link member 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.

The uc_sigmask member is the set of signals that are blocked when the context is activated. Further information can be found in sigprocmask(2).

The uc_stack member defines the stack used by the context. Further information can be found in sigaltstack(2).

The uc_mcontext member 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.

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

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).

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.