coroutine-sigaltstack: use helper for allocating stack memory

typedef struct {

    Coroutine base;

    void *stack;

    size_t stack_size;

    sigjmp_buf env;

} CoroutineSigAltStack;

Coroutine *qemu_coroutine_new(void)

{

    const size_t stack_size = COROUTINE_STACK_SIZE;

    CoroutineSigAltStack *co;

    CoroutineThreadState *coTS;

    struct sigaction sa;

     */

    co = g_malloc0(sizeof(*co));

    co->stack = g_malloc(stack_size);

    co->stack_size = COROUTINE_STACK_SIZE;

    co->stack = qemu_alloc_stack(&co->stack_size);

    co->base.entry_arg = &old_env; /* stash away our jmp_buf */

    coTS = coroutine_get_thread_state();

     * Set the new stack.

     */

    ss.ss_sp = co->stack;

    ss.ss_size = stack_size;

    ss.ss_size = co->stack_size;

    ss.ss_flags = 0;

    if (sigaltstack(&ss, &oss) < 0) {

        abort();

{

    CoroutineSigAltStack *co = DO_UPCAST(CoroutineSigAltStack, base, co_);

    g_free(co->stack);

    qemu_free_stack(co->stack, co->stack_size);

    g_free(co);

}