UCONTEXT_ALLOC(3C) Standard C Library Functions UCONTEXT_ALLOC(3C)

NAME

ucontext_alloc, ucontext_free - allocate and free ucontext structures

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <ucontext.h>

ucontext_t *
ucontext_alloc(uint32_t flags);

void
ucontext_free(ucontext_t *ucp);

DESCRIPTION

The ucontext_alloc() function allocates and initializes a ucontext_t
structure for subsequent use with functions such as getcontext_extd(2) or
swapcontext_extd(3C).

Traditionally applications declare the ucontext_t structure on the stack,
as part of another structure, or in other global data. Due to the advent
of extended states (such as the x86 xsave state) the traditional structure
is not sufficient to capture all state. The ucontext_alloc() function
determines the correct size for the current process to cover all of its
extended states in addition to the standard ucontext_t and then proceeds to
set up the other members of the ucontext_t to point at the additional
memory.

It is not recommended that the returned ucontext structure be used with
either getcontext(2) or swapcontext(3C). While the resulting calls will
work, they will not preserve that space for the extended state has been
allocated. No memory will be leaked as a result of that.

The ucontext_free() function is used to release all the memory associated
with ucp. ucp must have come from a prior call to ucontext_alloc(). If it
is not, then it is undefined as to what will happen to the program, but it
will result in eventual memory corruption. If ucp was declared on the
stack, as a structure member, as global data, or allocated in some way that
wasn't calling ucontext_alloc(), do not pass it to ucontext_free().

RETURN VALUES

Upon successful completion, the ucontext_alloc() function returns a pointer
to an allocated ucontext_t. Otherwise NULL is returned and errno is set to
indicate the error.

ERRORS

The ucontext_alloc() function will set errno based on the failure of the
underlying memory allocator. For more information and details on these
errors, see malloc(3C), the list of errors below may not be exhaustive.

The ucontext_alloc() function will fail if:

EINVAL The flags argument had unknown or unsupported values.

ENOMEM There was insufficient memory to allocate an extended
ucontext structure. See malloc(3C) for more
information.

EAGAIN There was insufficient memory to allocate an extended
ucontext structure, but the application could try again
later. See malloc(3C) for more information.

INTERFACE STABILITY

Committed

MT-LEVEL
Safe

SEE ALSO

illumos January 24, 2023 illumos