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Date:	Fri, 4 Dec 2015 14:25:39 -0500
Message-ID:	<CAPHm_==DDJg9CKkq2OVHT=on+dmH_-A8eWZFkUsHkETG-L2gqw@mail.gmail.com>
Subject:	another LoadLibrary question / crash (sorry)
From:	Mike Giancola <mikegiancola AT gmail DOT com>
To:	cygwin AT cygwin DOT com

Hi,

I apologize for asking the same question that has been asked so many
times - but I'm stuck.

I have a DLL built in Cygwin that I'm trying to call from a program
compiled in Visual Studio 2012. When I call LoadLibrary it's
successful, however calls to the APIs crash the program.

From what I've read, I understand I need to allocate "4k of scratch
space at the bottom of the stack" and call the  cygwin_dll_init first.
(From https://cygwin.com/faq/ section 6.19).

I haven't been able to find the how-cygtls-works.txt nor
winsup/testsuite/cygload - most of the links in old mail archives are
dead (some messages go back to 2007). That said, I've found cygload.cc
here: https://raw.githubusercontent.com/openunix/cygwin/master/winsup/testsuite/winsup.api/cygload.cc

Here, the code attempts to use some assembly to set the stack size:

#ifdef __GNUC__
  __asm__ (
    "movl %%fs:4, %0"
    :"=r"(stackbase)
    );
#else
  __asm
      {
        mov eax, fs:[4];
        mov stackbase, eax;
      }
#endif

However these lines crash the program. I've downloaded these exact
files (the .cc & .h) and compiled them using VS2012. When debugged /
run i get an access violation and crash. Note - i'm trying to run this
program as is, unmodified.

Is there a specific compiler flag i need to set in order to allow
these operations? I've turned off DEP, i've tried both set the entry
point to be cygloadCRTStartup then going back - reseting the entry
point and uncommenting the construction of the padding object line.
Both fail.

Does anyone happen to have a simple example - simply calling a
"fooapi" within a dll available? Is there any updated documentation
anywhere?

Thanks for the help!

mike

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