DMARC-Filter: OpenDMARC Filter v1.4.2 delorie.com 55RKlk7S1581722
Authentication-Results: delorie.com; dmarc=pass (p=none dis=none) header.from=cygwin.com
Authentication-Results: delorie.com; spf=pass smtp.mailfrom=cygwin.com
DKIM-Filter: OpenDKIM Filter v2.11.0 delorie.com 55RKlk7S1581722
Authentication-Results: delorie.com;
	dkim=pass (1024-bit key, unprotected) header.d=cygwin.com header.i=@cygwin.com header.a=rsa-sha256 header.s=default header.b=sFUrhGwU
X-Recipient: archive-cygwin AT delorie DOT com
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6CC46385C6D5
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1751057264;
	bh=PiJf/0/W9SIHsn7+wyuzsauQyQ/GC1alyoNjt/aj0r4=;
	h=Date:To:Cc:Subject:In-Reply-To:References:List-Id:
	 List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe:
	 From:Reply-To:From;
	b=sFUrhGwU8vF0G+dNNWncUJetKkGPgf57YNMYU26l6jpqp9/GY6XfoHLE2jE9ijPEH
	 bfeyrK8Q9Jz7mwJQuHmky/OMENPBqbt37X+oUliJ9aKDEde54faQrEiw27PoIJ7afI
	 KtYXig8LQjzXZy4dxh2lBxZsS7tbomfg/4k+tkvA=
X-Original-To: cygwin AT cygwin DOT com
Delivered-To: cygwin AT cygwin DOT com
DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 449023858408
ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 449023858408
ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1751057239; cv=none;
 b=oG6wsw4mZ1/xXOOcdpMoVB2nebFEwlfqnVkGan9L9M66S1zVjwndL7ozGc8ACeUi82j3FJmyxYUCYcJHvRZ8ZsTnz7i6yLaJQPCQo+yNa9iNFbpZLHuXGIJ2SKAtNz7g0Q2/2NHAsZw7UHvVF3Vn0BW5h4/jXHdaPBei1KJuAxA=
ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key;
 t=1751057239; c=relaxed/simple;
 bh=z4+CZhxgnGU9c1RtJdN2XF5nDoyTBcHmhw3O6ic8o8U=;
 h=DKIM-Signature:Date:To:From:Subject:Message-ID:MIME-Version;
 b=uX0s27nKB3jKkpotRNcgqy3EInasz/EIAJwg4Vgl43+Wx7bJMm7bzrBFDc9Pdu6Mx0YeNGEpmLEH6z1Db6gMT7tmi9BM3bJxhhwgLTQeS9G7mmYW2EnYpd7wy2gVQH8txXQJwemkEALZRUPhaDQPhQn62Z3PK02BIfmgiIO7vLo=
ARC-Authentication-Results: i=1; server2.sourceware.org
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 449023858408
Date: Fri, 27 Jun 2025 20:47:11 +0000
To: Jeremy Drake <cygwin AT jdrake DOT com>
Cc: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
Subject: Re: XSAVE-related segfaults observed under wine
Message-ID: <87tt403oac.fsf@protonmail.com>
In-Reply-To: <abda5210-ba7f-a4a0-5c0c-880367fec254@jdrake.com>
References: <87bjq9457k DOT fsf AT protonmail DOT com>
 <aF60VympSWbCeu2n AT calimero DOT vinschen DOT de>
 <abda5210-ba7f-a4a0-5c0c-880367fec254 AT jdrake DOT com>
Feedback-ID: 112775352:user:proton
X-Pm-Message-ID: 3a4855ffab35db9c520bb56ad13494cf636a8ac8
MIME-Version: 1.0
X-BeenThere: cygwin AT cygwin DOT com
X-Mailman-Version: 2.1.30
Precedence: list
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe: <https://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive: <https://cygwin.com/pipermail/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe: <https://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From: Pip Cet via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Pip Cet <pipcet AT protonmail DOT com>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Errors-To: cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com
Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>

"Jeremy Drake" <cygwin AT jdrake DOT com> writes:

> On Fri, 27 Jun 2025, Corinna Vinschen via Cygwin wrote:
>
>> Hi Pip,
>>
>> On Jun 27 14:41, Pip Cet via Cygwin wrote:
>> > My suggested fix is to align the value in %rbx to the next 64-byte
>> > multiple after the "cpuid" instruction is executed, by performing the
>> > assembler equivalent of $rbx += 63; $rbx &= -64; I tried this:
>> >
>> > diff --git a/winsup/cygwin/scripts/gendef b/winsup/cygwin/scripts/gendef
>> > index 861a2405b..d681fde3f 100755
>> > --- a/winsup/cygwin/scripts/gendef
>> > +++ b/winsup/cygwin/scripts/gendef
>> > @@ -232,6 +232,8 @@ sigdelayed:
>> >  	movl	\$0x0d,%eax
>> >  	xorl	%ecx,%ecx
>> >  	cpuid	# get necessary space for xsave
>> > +	addq	\$63, %rbx
>> > +	andq	\$-64, %rbx # align to next 64-byte multiple
>>
>> what about a oneliner instead by just aligning rsp?  As in
>>
>> >  	movq	%rbx,%rcx
>> >  	addq	\$0x48,%rbx # 0x18 for alignment, 0x30 for additional space
>
> If aligning via andq, does the 0x18 "for alignment" still need to be
> included?

If we align %rsp, as Corinna suggested, we don't need the 0x18.

If we do what my patch did and align %rbx, we do need to subtract 0x18,
because that's the amount by which our stack pointer is misaligned (it
was aligned to 64 bytes, then we pushed 13 8-byte registers).

Technically, instead of aligning %rbx to a multiple of 64 and adding
0x48, we could round it up to the next integer that's congruent to 0x18
modulo 0x40 and add 0x30, saving 64 bytes of stack space on some CPUs
(including, I believe, both of my PKU-enabled CPUs).

This may be a sour grapes scenario, but using xsavec or clearing only
part of the xsave64 area (the current code clears all of it) would be
other optimizations that might have more of an impact.

Pip


-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple