From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:48994)
	by lists.gnu.org with esmtp (Exim 4.71) (envelope-from <pl@kamp.de>)
	id 1bJxCx-0002bz-Aj
	for qemu-devel@nongnu.org; Mon, 04 Jul 2016 02:18:16 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <pl@kamp.de>) id 1bJxCv-0006fb-EG
	for qemu-devel@nongnu.org; Mon, 04 Jul 2016 02:18:14 -0400
Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:57049 helo=mx01.kamp.de)
	by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from <pl@kamp.de>)
	id 1bJxCv-0006fX-4h
	for qemu-devel@nongnu.org; Mon, 04 Jul 2016 02:18:13 -0400
References: <1467272240-32123-1-git-send-email-pl@kamp.de>
	<1467272240-32123-2-git-send-email-pl@kamp.de>
	<851cfb04-5e9d-6f9a-5932-09e697aa500e@twiddle.net>
	<6bc08536-27f5-e4b1-fc8b-4bb04a8655dc@twiddle.net>
From: Peter Lieven <pl@kamp.de>
Message-ID: <5779FF99.20605@kamp.de>
Date: Mon, 4 Jul 2016 08:18:01 +0200
MIME-Version: 1.0
In-Reply-To: <6bc08536-27f5-e4b1-fc8b-4bb04a8655dc@twiddle.net>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 1/6] oslib-posix: add helpers for stack
 alloc and free
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel/>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Richard Henderson <rth@twiddle.net>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, peter.maydell@linaro.org, mst@redhat.com, dgilbert@redhat.com, mreitz@redhat.com, pbonzini@redhat.com

Am 01.07.2016 um 22:49 schrieb Richard Henderson:
> On 07/01/2016 01:12 PM, Richard Henderson wrote:
>> 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();
>>> +    }
>
> Rare platforms now, but fwiw, this is incorrect for hppa and ia64.
>
> For hppa, stack grows up, so the guard page needs to be at the top.
>
> For ia64, there are two stacks, the "normal" program stack (grows down) and the register window stack (grows up).  The guard page goes in between.
>
> See e.g. glibc/nptl/allocatestack.c
>
> #ifdef NEED_SEPARATE_REGISTER_STACK
>           char *guard = mem + (((size - guardsize) / 2) & ~pagesize_m1);
> #elif _STACK_GROWS_DOWN
>           char *guard = mem;
> #elif _STACK_GROWS_UP
>           char *guard = (char *) (((uintptr_t) pd - guardsize) & ~pagesize_m1);
> #endif
>           if (mprotect (guard, guardsize, PROT_NONE) != 0)

It seems that ia64 needs even more care when allocating a stack, right?
Would you think it is ok to only handle _STACK_GROWS_DOWN and _STACK_GROWS_UP ?

Peter