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Subject:	RE: [BUG] cygwin-1.3.3-2 -- making auto-import dlls
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Date:	Wed, 19 Sep 2001 12:34:51 +1000
Message-ID:	<EA18B9FA0FE4194AA2B4CDB91F73C0EF08F197@itdomain002.itdomain.net.au>
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Thread-Topic:	[BUG] cygwin-1.3.3-2 -- making auto-import dlls
Thread-Index:	AcFAstptFTV0c4VbTQGwtkCoMsQ87wAAAL1A
From:	"Robert Collins" <robert DOT collins AT itdomain DOT com DOT au>
To:	"Charles Wilson" <cwilson AT ece DOT gatech DOT edu>, <cygwin AT cygwin DOT com>
X-MIME-Autoconverted:	from quoted-printable to 8bit by delorie.com id WAA08359

I went round this one with Paul's original patch.

Auto image base is bad (for cygwin).

Very bad.

Ok, now the scare is over, here is why:

Lemma: Cygwin1.dll is only relocatable if it is consistently relocated
to the same address in _all_ process's that load cygwin1.dll. Proof:
cygwin copies the process address space to fork, if references to
cygwin1.dll are not valid in the hild, the child will die badly.

Auto image base will conflict with cygwin1.dll semi-randomly. Because
other cygwin linked .dll's come before cygwin1.dll in the PE header
(don't know if this is due to link order, sorting of the file or
whathaveyou) cygwin1.dll is the last .dll. Thus when there is a
conflict, cygwin1.dll gets relocated.

The problem: bash does not depend on these conflicting .dll's, so every
process started that does depend on them will fail to initialise.

Solution: don't use auto-image-base. The overhead from relocation is
quite low, why not let windows just do its thing.

Rob

> -----Original Message-----
> From: Charles Wilson [mailto:cwilson AT ece DOT gatech DOT edu]
> Sent: Wednesday, September 19, 2001 12:19 PM
> To: cygwin AT cygwin DOT com
> Subject: Re: [BUG] cygwin-1.3.3-2 -- making auto-import dlls
> 
> 
> Christopher Faylor wrote:
> 
> > On Wed, Sep 19, 2001 at 10:38:24AM +0900, Jong B. Lee wrote:
> > 
> >>Attached file is a part of Charles Wilson's dllhelpers-0.2.7
> >>(originally from Mumit Khan's).  This dllhelpers used to be 
> introduced
> >>as an example for those people who ask how to build and use dlls on
> >>cygwin, and its' good.
> >>
> >>It fails to run on cygwin 1.3.3-2 with a heap error.  C++/F77 cases
> >>work good.  Only C examples fail to execute.  This error 
> does not occur
> >>on cygwin-1.3.2-1.
> >>
> > 
> > Change the DLL load address to be something besides 
> 61500000 and it will work.
> > 
> 
> 
> Does this mean that something needs to be fixed in the 
> "--auto-image-base" code?  Since the dllhelpers example uses 
> that flag, 
> *I* would expect ld to NOT generate a known bad load address.
> 
> 
> --Chuck
> 
> 
> 
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