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

Larry Hall (Cygwin) reply-to-list-only-lh@cygwin.com
Fri Apr 20 17:58:00 GMT 2012

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.



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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