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Date: Fri, 20 Apr 2012 13:40:44 -0400
From: "Larry Hall (Cygwin)" <reply-to-list-only-lh AT cygwin DOT com>
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To: cygwin AT cygwin DOT com
Subject: Re: Why /usr/bin/*.dll must be executable?
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On 4/20/2012 1:32 PM, De-Jian Zhao wrote:
> On 2012-4-21 0:27, Corinna Vinschen wrote:
>> On Apr 21 00:17, De-Jian Zhao wrote:
>>> On 2012-4-20 21:07, Václav Zeman wrote:
>>>> On 20 April 2012 15:02, De-Jian Zhao wrote:
>>>>> Hi,
>>>>>
>>>>> When I type "cyg" and Tab, many executables starting with "cyg" are listed
>>>>> (Display all 262 possibilities? (y or n) y). I find that many of them are
>>>>> *.dll libraries under /usr/bin/. This is inconvenient to find the real
>>>>> executable applications (*.exe). Since *.dll files are only libraries,
>>>>> they
>>>>> are not necessary to have the attribute of "x". Thus, I run the command
>>>>> "chmod a-x /usr/bin/*.dll". Unexpectedly, cygwin is corrupted. I closed
>>>>> the
>>>>> terminal and failed to restart Cygwin. I started my older version of
>>>>> Cygwin
>>>>> (I did not deleted it after installing a new version), and added "x" to
>>>>> the
>>>>> previous *.dll files. The dead Cygwin revived.
>>>>>
>>>>> I am confused why /usr/bin/*.dll should be executable. I thought they were
>>>>> only library files. When I tried to run a dll file, bash says "cannot
>>>>> execute binary file". Are there some hidden stories?
>>>> DLLs are executables thus they need the +x bit. This is a Windows thing.
>>>>
>>> If this is a windows thing, removing the x bit should not affect
>>> Cygwin. Instead, Cygwin is corrupted after removing the x bit.
>> Windows requires the x bit for DLLs to be loadable as executable code
>> into the address space of a process. As Václav wrote, it's a Windows
>> thing.
>
> Can Windows see the rwx bits assigned by Cygwin to the files? I tried
> removing the x bit of an executable file blastall.exe (chmod a-x
> blastall.exe); the file can not be executed under Cygwin, but still can be
> executed under cmd console of Windows. It seems that Windows does not honor
> the rwx bits assigned by Cygwin.
>
> Is there a detailed description of the starting process of Cygwin system?
> Or, how does Cygwin interact with *.dll files?
>
> After starting Cygwin, I ran "chmod a-x /usr/bin/cygperl5_10.dll" and perl
> could not be started any more. This could be cured by ran "chmod a+x
> /usr/bin/cygperl5_10.dll". It seems to me that the Cygwin binary executables
> will communicate with their corresponding *.dll files when executed. The
> *.dll provide the required functions and subroutines and that's enough.
> There is no need to mark *.dll with an x bit.
>
> I have no strong background of computer science. Maybe there is some basic
> knowledge beyond my imagination. Hope you can help disclose it to me. Thanks.

Cygwin DLLs are no different than native Windows DLLs when it comes to
loading them.  The Windows loader is responsible for loading them.  So
we're stuck with whatever restrictions the Windows loader imposes on
Windows apps.


-- 
Larry

_____________________________________________________________________

A: Yes.
 > Q: Are you sure?
 >> A: Because it reverses the logical flow of conversation.
 >>> Q: Why is top posting annoying in email?

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