swapcontext() and Segmentation Fault

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LEARN ABOUT NETBSD

makecontext

MAKECONTEXT(3)						   BSD Library Functions Manual 					    MAKECONTEXT(3)

NAME

     makecontext, swapcontext -- manipulate user contexts

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <ucontext.h>

     void
     makecontext(ucontext_t *ucp, void (*func)(), int argc, ...);

     int
     swapcontext(ucontext_t * restrict oucp, ucontext_t * restrict ucp);

DESCRIPTION

     The makecontext() function modifies the object pointed to by ucp, which has been initialized using getcontext(2).	When this context is
     resumed using swapcontext() or setcontext(2), program execution continues as if func had been called with the arguments specified after argc
     in the call of makecontext().  The value of argc must be equal to the number of integer arguments following it, and must be equal to the num-
     ber of integer arguments expected by func; otherwise, the behavior is undefined.

     Before being modified using makecontext(), a stack must be allocated for the context (in the uc_stack member), and a context to resume after
     func has returned must be determined (pointed to by the uc_link member); otherwise, the behavior is undefined.  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 swapcontext() function saves the current context in the object pointed to by oucp, sets the current context to that specified in the
     object pointed to by ucp, and resumes execution.  When a context saved by swapcontext() is restored using setcontext(2), execution will
     resume as if the corresponding invocation of swapcontext() had just returned (successfully).

RETURN VALUES

     The makecontext() function returns no value.

     On success, swapcontext() returns a value of 0, Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

     The swapcontext() function will fail if:

     [EFAULT]		The oucp argument or the ucp argument points to an invalid address.

     [EINVAL]		The contents of the datum pointed to by ucp are invalid.

SEE ALSO

     _exit(2), getcontext(2), setcontext(2), ucontext(2)

STANDARDS

     The makecontext() and swapcontext() functions conform to X/Open System Interfaces and Headers Issue 5 (``XSH5'') and IEEE Std 1003.1-2001
     (``POSIX.1'').

     The IEEE Std 1003.1-2004 (``POSIX.1'') revision marked the functions makecontext() and swapcontext() as obsolete, citing portability issues
     and recommending the use of POSIX threads instead.  The IEEE Std 1003.1-2008 (``POSIX.1'') revision removed the functions from the specifica-
     tion.

     The standard does not clearly define the type of integer arguments passed to func via makecontext(); portable applications should not rely on
     the implementation detail that it may be possible to pass pointer arguments to functions.	This may be clarified in a future revision of the
     standard.

HISTORY

     The makecontext() and swapcontext() functions first appeared in AT&T System V Release 4 UNIX.

BSD
								    May 4, 2012 							       BSD

Programming