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

De-Jian Zhao dejian.zhao@gmail.com
Fri Apr 20 18:21:00 GMT 2012

On 2012-4-21 1:57, Larry Hall (Cygwin) wrote:
> On 4/20/2012 1:47 PM, De-Jian Zhao wrote:
>> 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?
> Cygwin is not an O/S.  The basis for Cygwin is the emulation _DLL_, 
> cygwin1.dll.  Cygwin executables and DLLs are Windows binaries, 
> subject to whatever limitations the Windows loader has.  That's it.  
> If you're not happy about that, you should complain to MS about it.
Then, what limitations does the Windows loader have?
As far as I know, there is no x bits for windows, right? How does the 
"chmod a-x" affect the file behavior under Windows if this is a Windows 
thing? I am completely confused. When I ran "chmod a-x *.dll", I assumed 
that these dll files were not executed directly under Cygwin or Windows; 
they were just some files storing the required functions or something; 
removing the x bits should not affect the behavior of Cygwin and 
Windows. If have run "chmod a-x" on the Windows system dll files, that 
will lead to the corruption of Windows, right? Thank God. I didn't do that.

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