DMARC-Filter:	OpenDMARC Filter v1.4.2 delorie.com 62D5OG54370075
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 62D5OG54370075
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=vlOFU+WK
X-Recipient:	archive-cygwin AT delorie DOT com
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org 1256F4C31822
DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1773379455;
	bh=3wdjJ8lDFTaxaw85BQuKJskAqcQm+VligiORxgZNwXY=;
	h=Date:To:In-Reply-To:References:Subject:List-Id:List-Unsubscribe:
	List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:
	From;
	b=vlOFU+WKIO7QLrY2CTTYkRAO6LMaec7pt/aimFjgxmNDu70SmlhydSZbz3rzdeYTT
	UDWmZPjJyaV+RPtY/ZVDf0Gujl2b4k7RHRIyISC2iwPKBPw3miuYj6ZuQwHkM9YqjL
	oAfplw99NPWjYe79/myCleNtEvQn1yl6aTHXMk0E=
X-Original-To:	cygwin AT cygwin DOT com
Delivered-To:	cygwin AT cygwin DOT com
DMARC-Filter:	OpenDMARC Filter v1.4.2 sourceware.org 666814BBC0C6
ARC-Filter:	OpenARC Filter v1.0.0 sourceware.org 666814BBC0C6
ARC-Seal:	i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1773379404; cv=none;
	b=FJzFCc2lPWN8NwKP2S4MjGbGksb3KFBLbyDRMzHRBlDXnHGx4bqDobFMvrjl1g4AislBIpMAfsZkXGPzW9FpJw0vZh9cIY2p0xN9iXssrqmpo5ykZoPhXlYxgH6MjxxbFnJnJjGZFLdyg1zuOsCxjk2aCranihxGqOmLtl6EEqU=
ARC-Message-Signature:	i=1; a=rsa-sha256; d=sourceware.org; s=key;
	t=1773379404; c=relaxed/simple;
	bh=0+VfEVFX4spgrGuBksD1HYI7OBXNstVAl7ki80VvlB4=;
	h=DKIM-Signature:Date:From:To:Message-ID:Subject:MIME-Version;
	b=A7OJV4lzxzkHe/lXnzUz2TTDRJYG9w9UnWV1OEz9KaeFzEhlSwXZRZR0BRxrSQ3okFyz87XWdhohdsLrxdqxmvQ8lFNLcdPGIn8siNet4UBtSQobWaefs4ymmamdrFgFDcF7GAXC+WKNcCySjsnGZ5zAlHeOdmCadzKSvbT20ZY=
ARC-Authentication-Results:	i=1; server2.sourceware.org
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org 666814BBC0C6
Date:	Thu, 12 Mar 2026 22:23:20 -0700 (PDT)
To:	KENNON J CONRAD via Cygwin <cygwin AT cygwin DOT com>,
	Jon Turney <jon DOT turney AT dronecode DOT org DOT uk>
Message-ID:	<275464098.52532.1773379400076@connect.xfinity.com>
In-Reply-To:	<533298615.52416.1773378911433@connect.xfinity.com>
References:	<547312365 DOT 1464244 DOT 1771958282029 AT connect DOT xfinity DOT com>
	<aZ7PrbisVR1R4A7v AT dimstar DOT local DOT net>
	<1670201592 DOT 1489273 DOT 1772043520008 AT connect DOT xfinity DOT com>
	<e91d8b5b-2690-4271-aa74-e6226440e33d AT SystematicSW DOT ab DOT ca>
	<1044918836 DOT 1507810 DOT 1772086967212 AT connect DOT xfinity DOT com>
	<abd66c5d-6bcd-40ae-b7c6-a8a3325aca8e AT dronecode DOT org DOT uk>
	<533298615 DOT 52416 DOT 1773378911433 AT connect DOT xfinity DOT com>
Subject:	Re: Memmove causing program crashes, giving SIGTRAP in GDB(?)
MIME-Version:	1.0
X-Priority:	3
Importance:	Normal
X-Mailer:	Open-Xchange Mailer v7.10.6-Rev83
X-Originating-IP:	::ffff:50.47.202.14
X-Originating-Port:	33754
X-Originating-Client:	open-xchange-appsuite
X-CMAE-Envelope:	MS4xfMjdIUaAxNuHCG70p1opcwmYZGxKss6j72J6iPqCGz5Rhfpdj5HClTxDg1u3RALe3T8DCP3fSP4fDygdBBH15+2Zbgx57n3n50Nf0VSCRI3rWKpEjNRS
	qP8rSa7VtE6bInLxUXiC4x2F0DzpMjFyhmEO6gdLqJmSazXGHYwmruZWw5esYLy+jNfOmp9DnE/rUxjeq0PH9m7TQui9gEEiV+DY5eM9s15rV5YQN2ejFXDV
	cS3o23aKF20L/0xVDaDxh4PxqhtE/Hl8q/QEHTcevEk=
X-BeenThere:	cygwin AT cygwin DOT com
X-Mailman-Version:	2.1.30
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:	KENNON J CONRAD via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	KENNON J CONRAD <kennonconrad AT comcast DOT net>
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>

Corrections:

Elements 973 - 976 would be moved on the next iteration of the REP MOVSQ.
REP MOVSQ made it through 17 iterations

> On 03/12/2026 10:15 PM PDT KENNON J CONRAD via Cygwin <cygwin AT cygwin DOT com> wrote:
> 
>  
> Thanks, Jon.  Setting cygwin-exceptions on does change the picture considerably,
> but the picture of exactly what is happening is still cloudy for me.
> 
> The program breaks at the same spot in memmove, which is now in frame 0:
> REP MOVSQ %ds(%rsi),%es(%rdi)
> 
> but now GDB says "received signal SIGSEGV, Segmentation fault."
> 
> The EFLAGS register value is 0x10687 [ CF PF SF IF DF RF ].
> So DF is set (as it should be), which is different than without exceptions on.
> 
> ds contains 0x2b (not relevant?)
> es contains 0x2b (not relevant?)
> rsi contains 0xa00034c1a
> rdi contains 0xa00034c1c
> The uint16_t array starts at address 0xa00034480
> Array elements 781 - 1045 are being moved to 782 - 1046 (backward move).
> Elements 973 - 980 would be moved on the next iteration of the REP MOVSQ.
> 
> I see no obvious reason for the segmentation fault.  The array address looks correct,
> the array indexes are valid, and the REP MOVSQ made it through 8 iterations before
> the SIGSEGV happened, and the program does not crash using alternative code in place
> of the memmove call.
> 
> Is it possible some interrupt routine doesn't handle DF being set when it starts and
> gets a segmentation fault that GDB would detect at this point in the code?
> 
> 
> > I'd add to that a reference to [1]
> > 
> > [1] https://cygwin.com/faq.html#faq.programming.debugging-cygwin
> > 
> > Unfortunately, when investigating exceptions inside the cygwin dll, it's 
> > necessary to 'set cygwin-exceptions on', which will cause the debugger 
> > to actually stop at the point of the exception.
> > 
> > (This explains why the specific exception is SIGTRAP, and why you get 
> > the all the extra frames for exception handling below memmove in the 
> > backtrace)
> >
> 
> -- 
> 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

-- 
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

- Raw text -