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Date:	Sat, 21 Apr 2012 01:32:22 +0800
From:	De-Jian Zhao <dejian DOT zhao AT gmail DOT com>
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Subject:	Re: Why /usr/bin/*.dll must be executable?
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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.


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