man pages section 2: System Calls

setcontext(2)

Name

getcontext, setcontext– get and set current user context

Synopsis

#include <ucontext.h>

int getcontext(ucontext_t *ucp);

int setcontext(const ucontext_t *ucp);

Description

The getcontext() function initializes the structure pointed to by ucp to the current user context of the calling process. The ucontext_t type that ucp points to defines the user context and includes the contents of the calling process' machine registers, the signal mask, and the current execution stack.

The setcontext() function restores the user context pointed to by ucp. A successful call to setcontext() does not return; program execution resumes at the point specified by the ucp argument passed to setcontext(). The ucp argument should be created either by a prior call to getcontext(), or by being passed as an argument to a signal handler. If the ucp argument was created with getcontext(), program execution continues as if the corresponding call of getcontext() had just returned. If the ucp argument was created with makecontext(3C), program execution continues with the function passed to makecontext(3C). When that function returns, the process continues as if after a call to setcontext() with the ucp argument that was input to makecontext(3C). If the ucp argument was passed to a signal handler, program execution continues with the program instruction following the instruction interrupted by the signal. If the uc_link member of the ucontext_t structure pointed to by the ucp argument is equal to 0, then this context is the main context, and the process will exit when this context returns. The effects of passing a ucp argument obtained from any other source are unspecified.

Return Values

On successful completion, setcontext() does not return and getcontext() returns 0. Otherwise, -1 is returned.

Errors

No errors are defined.

Usage

When a signal handler is executed, the current user context is saved and a new context is created. If the thread leaves the signal handler via longjmp(3UCB), then it is unspecified whether the context at the time of the corresponding setjmp(3UCB) call is restored and thus whether future calls to getcontext() will provide an accurate representation of the current context, since the context restored by longjmp(3UCB) may not contain all the information that setcontext() requires. Signal handlers should use siglongjmp(3C) instead.

Portable applications should not modify or access the uc_mcontext member of ucontext_t. A portable application cannot assume that context includes any process-wide static data, possibly including errno. Users manipulating contexts should take care to handle these explicitly when required.

Attributes

See attributes(5) for descriptions of the following attributes:

`ATTRIBUTE TYPE`	ATTRIBUTE VALUE
Interface Stability	Standard