X-Recipient:	archive-cygwin AT delorie DOT com
DomainKey-Signature:	a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:from:to:subject:date:message-id:references
	:in-reply-to:content-type:content-transfer-encoding
	:mime-version; q=dns; s=default; b=VLpUl+2xZFV8xV80Aq4rChZJA9gIt
	fenut2xkW+HdZX+L1m3hFk6p9mlVC2WJATYMLBeKmZ8dFyRz/Zl8O1LGQxGh1Jqs
	xOPhvCUW3PUqrel84aIcNN5KG9Jl6GWEz9B8EyFsDwCTqvRa1HtG3ArAn+Pg4hlL
	HBhcEYHK2k6rnY=
DKIM-Signature:	v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:from:to:subject:date:message-id:references
	:in-reply-to:content-type:content-transfer-encoding
	:mime-version; s=default; bh=fqDre2V9vXXbtfTKs6lRU4/AhRU=; b=rzU
	+iQ+kFneKp5V4SElqV9mH7MXCL8rCAsxfr/v5cSRroaJY6Zy7rEfbM4htZj27UID
	N4E+XDj3QES6PknmuHnBrC5vJj/KXnVvtxto9LM3t1Vhxdv0wVwSUuiaPIDSiSD3
	kSujggaCqi0ekJeSQ9lQqfNOfpYFDZQPBNk8loCA=
Mailing-List:	contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id:	<cygwin.cygwin.com>
List-Subscribe:	<mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive:	<http://sourceware.org/ml/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender:	cygwin-owner AT cygwin DOT com
Mail-Followup-To:	cygwin AT cygwin DOT com
Delivered-To:	mailing list cygwin AT cygwin DOT com
Authentication-Results:	sourceware.org; auth=none
X-Virus-Found:	No
X-Spam-SWARE-Status:	No, score=-1.1 required=5.0 tests=AWL,BAYES_00,KAM_LAZY_DOMAIN_SECURITY,KAM_NUMSUBJECT,MIME_BASE64_BLANKS,RCVD_IN_DNSWL_LOW autolearn=no version=3.3.2 spammy=H*M:local, Hx-spam-relays-external:sk:mail.au, H*RU:sk:mail.au, reserved
X-HELO:	outmail148107.authsmtp.com
From:	David Allsopp <David DOT Allsopp AT cl DOT cam DOT ac DOT uk>
To:	"cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject:	RE: Regression for OCaml introduced by rebase 4.4.4
Date:	Fri, 9 Feb 2018 13:19:35 +0000
Message-ID:	<E51C5B015DBD1348A1D85763337FB6D90189A899B2@Remus.metastack.local>
References:	<000001d3a0d2$9f604860$de20d920$@cl.cam.ac.uk> <20180208151549 DOT GA32555 AT calimero DOT vinschen DOT de> <E51C5B015DBD1348A1D85763337FB6D90189A8933F AT Remus DOT metastack DOT local> <20180209114048 DOT GK30794 AT calimero DOT vinschen DOT de> <20180209131141 DOT GL30794 AT calimero DOT vinschen DOT de>
In-Reply-To:	<20180209131141.GL30794@calimero.vinschen.de>
MIME-Version:	1.0
X-Server-Quench:	e0cd1820-0d9b-11e8-9f3b-9cb654bb2504
X-AuthReport-Spam:	If SPAM / abuse - report it at: http://www.authsmtp.com/abuse
X-AuthRoute:	OCd1ZAARAlZ5RRob BmUtCCtbTh09DhZI RxQKKE1TKxwUVhJa I0lFL1x7O0wTWlBf HTVUBhpUWUIHDDFq aQpQZRVcYUBPVg9p VwZLQ1FMFQVtHx4A BAAfUx1tdQBZeTA3 ZE8WJCEiAUR/dEZ/ RwBRFmoHKzJgOzQe WEJYagMAeVFXfx4Q Yk12AnBffGxUNHxl QwU5ZW1pYSNlBXYd eAwCN18JWkcMGHYy QApKOh4mGElNRiMv NRsqN1UREA4bIw0o PFEoQl9Qb1lOTFE2
X-Authentic-SMTP:	61633634383431.1039:706
X-AuthFastPath:	0 (Was 255)
X-AuthSMTP-Origin:	213.105.212.114/25
X-AuthVirus-Status:	No virus detected - but ensure you scan with your own anti-virus system.
X-IsSubscribed:	yes
X-MIME-Autoconverted:	from base64 to 8bit by delorie.com id w19DJoIP014888

Corinna Vinschen wrote:
> On Feb  9 12:40, Corinna Vinschen wrote:
> > On Feb  9 11:29, David Allsopp wrote:
> > > > Apart from that, not only Cygwin DLLs but also the Windows system
> > > > DLLs are all loaded and relocated to the area beyond 0x1:80000000,
> > > > so relocation beyond the 32 bit address space is no generic
> > > > problem in Windows.  Why isn't that possible in FlexDLL?  I don't
> understand this.
> > > > To me this looks like a bug in FlexDLL, not a requirement to let
> > > > certain DLLs slip through the cracks.
> > >
> > > There's a more full explanation of what and why for flexdll here:
> > > https://github.com/alainfrisch/flexdll/blob/master/README.md. I
> > > believe it's not unrelated to some of the black magic going on in
> > > Cygwin's autoload.cc, but without (at least at the moment), quite as
> > > much self-modifying code.
> > > [...]
> > > I guess one can argue over whether that's a bug or a limitation, but
> > > the problem we face is that we can engineer it so that our DLLs and
> > > executables are within a 2GB range (having looked again at this in
> > > even more detail, we could just as readily do this with addresses >
> > > 0x200000000), but we still run the risk of rebase messing up the
> DLLs.
> > >
> > > However, we'll scratch our heads some more on possible alternative
> > > solutions, since having a flag for DLLs which says "keep us within a
> > > 2GB range somewhere" sounds even more less likely to get merged than
> > > my previous suggestion.
> >
> > Two points:
> >
> > - You are aware that the main executable of 64 bit Cygwin processes
> are
> >   loaded to 0x1:00400000, right?  The 2 GB offset problem is already
> >   imminent.
> 
> ...and you must not use the 0x0:80000000 - 0x1:00000000 area because
> that's reserved for thread stacks.
> 
> To clarify, the full layout requirements:
> 
> - 0x0:00000000 - 0x0:80000000	Windows
> - 0x0:80000000 - 0x1:00000000	Cygwin pthreads (including main thread)
> - 0x1:00000000 - 0x1:80000000	Executable
> - 0x1:80000000 - 0x2:00000000	Cygwin DLL
> - 0x2:00000000 - 0x4:00000000	Rebased DLLs
> - 0x4:00000000 - 0x6:00000000	Non-rebased DLLs (hashed default
> addresses
> 				generated by binutils ld with
> 				-auto-image-based (default on Cygwin))
> - 0x6:00000000			Start Address Heap, growing upwards
> - 0x8:00000000 - 0x700:00000000	Mmaps, allocated downwards
> - 0x700:00000000 and beyond	Windows

Thanks for this (and your time on this question generally!). I reckon that the jump tables will sort this and we'll be able to stop doing horrible things with --image-base completely, which should mean that flexlink (and therefore OCaml too) will start properly respecting the Cygwin address space layout! It's a shame that the layout means that the trampolines would always be needed, but I very much doubt their overhead will be significant in any program.


David

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

- Raw text -