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.Dd May 4, 2012 .Dt MAKECONTEXT 3 .Os .Sh NAME .Nm makecontext , .Nm swapcontext .Nd manipulate user contexts .Sh LIBRARY .Lb libc .Sh SYNOPSIS n ucontext.h .Ft void .Fn makecontext "ucontext_t *ucp" "void (*func)()" "int argc" ... .Ft int .Fn swapcontext "ucontext_t * restrict oucp" "ucontext_t * restrict ucp" .Sh DESCRIPTION The .Fn makecontext function modifies the object pointed to by .Fa ucp , which has been initialized using .Xr getcontext 2 . When this context is resumed using .Fn swapcontext or .Xr setcontext 2 , program execution continues as if .Fa func had been called with the arguments specified after .Fa argc in the call of .Fn makecontext . The value of .Fa argc must be equal to the number of integer arguments following it, and must be equal to the number of integer arguments expected by .Fa func ; otherwise, the behavior is undefined.
p Before being modified using .Fn makecontext , a stack must be allocated for the context (in the .Fa uc_stack member), and a context to resume after .Fa func has returned must be determined (pointed to by the .Fa uc_link member); otherwise, the behavior is undefined. If .Fa 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.
p The .Fn swapcontext function saves the current context in the object pointed to by .Fa oucp , sets the current context to that specified in the object pointed to by .Fa ucp , and resumes execution. When a context saved by .Fn swapcontext is restored using .Xr setcontext 2 , execution will resume as if the corresponding invocation of .Fn swapcontext had just returned (successfully). .Sh RETURN VALUES The .Fn makecontext function returns no value.
p On success, .Fn swapcontext returns a value of 0, Otherwise, -1 is returned and .Va errno is set to indicate the error. .Sh ERRORS The .Fn swapcontext function will fail if: l -tag -width Er t Bq Er EFAULT The .Fa oucp argument or the .Fa ucp argument points to an invalid address. t Bq Er EINVAL The contents of the datum pointed to by .Fa ucp are invalid. .El .Sh SEE ALSO .Xr _exit 2 , .Xr getcontext 2 , .Xr setcontext 2 , .Xr ucontext 2 .Sh STANDARDS The .Fn makecontext and .Fn swapcontext functions conform to .St -xsh5 and .St -p1003.1-2001 .
p The .St -p1003.1-2004 revision marked the functions .Fn makecontext and .Fn swapcontext as obsolete, citing portability issues and recommending the use of .Tn POSIX threads instead. The .St -p1003.1-2008 revision removed the functions from the specification.
p f -symbolic The standard does not clearly define the type of integer arguments passed to .Fa func via .Fn makecontext ; portable applications should not rely on the implementation detail that it may be possible to pass pointer arguments to functions. .Ef This may be clarified in a future revision of the standard. .Sh HISTORY The .Fn makecontext and .Fn swapcontext functions first appeared in .At V.4 .