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

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, VÃclav Zeman wrote:
On 20 April 2012 15:02, De-Jian Zhao wrote:

When I type "cyg" and Tab, many executables starting with "cyg" are
(Display all 262 possibilities? (y or n) y). I find that many of them
*.dll libraries under /usr/bin/. This is inconvenient to find the real
executable applications (*.exe). Since *.dll files are only libraries,
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
terminal and failed to restart Cygwin. I started my older version of
(I did not deleted it after installing a new version), and added "x" to
previous *.dll files. The dead Cygwin revived.

I am confused why /usr/bin/*.dll should be executable. I thought they
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 VÃclav wrote, it's a Windows

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.

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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