Re: [Qemu-devel] [PATCH 1/6] oslib-posix: add helpers for stack alloc and free

[Richard Henderson]

On 06/30/2016 12:37 AM, Peter Lieven wrote:
> +void *qemu_alloc_stack(size_t sz)
> +{
> +    /* allocate sz bytes plus one extra page for a guard
> +     * page at the bottom of the stack */
> +    void *ptr = mmap(NULL, sz + getpagesize(), PROT_NONE,
> +                     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +    if (ptr == MAP_FAILED) {
> +        abort();
> +    }
> +    if (mmap(ptr + getpagesize(), sz, PROT_READ | PROT_WRITE,
> +        MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0) == MAP_FAILED) {
> +        abort();
> +    }

Why two mmap instead of mmap + mprotect?


r~