Why /usr/bin/*.dll must be executable?

De-Jian Zhao dejian.zhao@gmail.com
Fri Apr 20 17:47:00 GMT 2012

On 2012-4-21 1:40, Larry Hall (Cygwin) wrote:
> 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.

Yes. But does Windows loader can see the x bit assigned by Cygwin, a 
quite different OS?

At least, *.exe does not respect or even is blind to the -x operation of 
Cygwin, as abovementioned.

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