getcontext(2) - Linux man page

Name

getcontext, setcontext - get or set the user context

Synopsis

#include <ucontext.h>

int getcontext(ucontext_t *ucp);
int setcontext(const ucontext_t *ucp);

where:

ucp
points to a structure defined in <ucontext.h> containing the signal mask, execution stack, and machine registers.

Description

getcontext(2) gets the current context of the calling process, storing it in the ucontext struct pointed to by ucp.

setcontext(2) sets the context of the calling process to the state stored in the ucontext struct pointed to by ucp. The struct must either have been created by getcontext(2) or have been passed as the third parameter of the sigaction(2) signal handler.

The ucontext struct created by getcontext(2) is defined in <ucontext.h> as follows: 

typedef struct ucontext
  {
      unsigned long int uc_flags;
      struct ucontext *uc_link;
      stack_t uc_stack;
      mcontext_t uc_mcontext;
      __sigset_t uc_sigmask;
      struct _fpstate __fpregs_mem;
    } ucontext_t;

Return Values

getcontext(2) returns 0 on success and -1 on failure. setcontext(2) does not return a value on success and returns -1 on failure.

Standards

These functions comform to: XPG4-UNIX.

Notes

When a signal handler executes, the current user context is saved and a new context is created by the kernel. If the calling process leaves the signal handler using longjmp(2), the original context cannot be restored, and the result of future calls to getcontext(2) are unpredictable. To avoid this problem, use siglongjmp(2) or setcontext(2) in signal handlers instead of longjmp(2).

See Also

sigaction(2), sigaltstack(2), sigprocmask(2), sigsetjmp(3), setjmp(3).

Referenced By

pth(3), swapcontext(2), swapcontext(3)