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Re: Windows make invoking cygwin sh bug

From: Alex Khripin
Subject: Re: Windows make invoking cygwin sh bug
Date: Fri, 18 Mar 2011 09:42:05 -0400

This is a fix I considered making to our build system. It would not be that hard to cygwin-ify our executable calls (there's not that many we call).

I don't think that is an optimal solution, because our build system is kind of a sprawling, out of control thing. Nobody is really in charge of it. So, at some point, someone will go and add another call to a windows-style program. Unless I can somehow cause _only_ POSIX paths to work -- and give an error if someone calls c:/moc.exe -- I won't be entirely happy. But your solution is basically how I would do the conversion.

I do want to correct you: GNU make _does_ know that it is being used with Cygwin. When you build GNU make on Windows, you have to specify, in config.h.W32, that it is going to be calling the Cygwin shell. It is based on that compiler option that it knows, for example, that nested double quotes should be escaped as "" instead of \". Here's a quote
 * Define if you have the Cygnus "Cygwin" GNU Windows32 tool set.
/*#define HAVE_CYGWIN_SHELL 1 */

There is a possibility that is perhaps a little more annoying - if Cygwin's behavior changes between versions.

On Fri, Mar 18, 2011 at 4:02 AM, tom honermann <address@hidden> wrote:
As you noted, this is not a defect in GNU make, but rather a defect in Cygwin (CYGWIN=noglob doesn't work as documented - I've come across this as well), and, essentially, incorrectly written makefiles.

Cygwin is an implementation of POSIX for Windows and therefore uses POSIX style path names.  It does have limited support for handling Windows native path names, but you'll likely have limited success getting your makefiles working well using native path names.  I recommend you make use of the 'cygpath' utility to convert path names to what Cygwin expects.  I've seen this done with make variables like the following:

  N2PP=$(foreach path,$(1),$(shell $(CYGWIN_HOME)/bin/cygpath.exe -u
  $(subst \,\\,$(path))))

N2PP stands for "Native to POSIX Path".  Assuming you are using the Win32 GNU make port (not the Cygwin port), this can be used something like:

       $(call N2PP,c:\foo) 1 "2 3" 4

Note that GNU make does not assume or know that the shell being used is the Cygwin shell, so a patch may not be appropriate.


On 3/17/2011 6:26 PM, Alex Khripin wrote:
Hi guys,
Short summary: there's a bug (I blame Cygwin, but want to fix make) in running commands that start with a drive letter when using Windows make and Cygwin sh

I've run into a problem running in our environment.

We run windows make (3.82) and use Cygwin (our make is compiled appropriately)

In this situation, normally, when make invokes a command, like
foo 1 "2 3" 4
It runs it like this:
sh.exe -c "foo 1 ""2 3"" 4"

This is passed to the cygwin sh binary, where the loader takes the command line and turns it into argv. Everything works great.

Unless the command is
c:/foo 1 "2 3" 4
In which case, it still gets called the same way
sh.exe -c "c:/foo 1 ""2 3"" 4"

The cygwin loader, though, doesn't treat this case the same way - for reasons explained below, this runs the equivalent of
c:/foo 1 2 "3 4"

I'd call this a cygwin problem - but they're not going to change how their loader works. There's probably many programs that rely on that behavior.
First, a test to show exactly what is going on - let's try a simple Cygwin program:
#include <stdio.h>
int main(int argc, char **argv) {
   int i;
   for (i = 1; i < argc; i++) printf("%d : %s\n", i, argv[i]);
   return 0;

**************** Normal program name *****************
c:\cygwin\home\akhripin>args "foo 1 ""2 3"" 4"
1 : foo 1 "2 3" 4
***************** DOS'y program name ****************
c:\cygwin\home\akhripin>args "c:/foo 1 ""2 3"" 4"
1 : c:/foo 1 \2 3\ 4

Look at those random \'s that appear! I've done some cygwin source reading, and apparently, parameters that start with letter-colon get treated differently.

My first attempt was to try setting CYGWIN=noglob But with that enabled, you can't get a double quote through to sh.exe at all - no kind of escaping will do

After extensive experimentation and source reading, I've determined that you cannot get the same method of escaping " and \ to work both for parameters that start with a drive letter and those that do not. Thus, I propose the following.

**************** Proposed fix **************
When building the command line for cygwin (to be passed tinto CreateProcess), look for arguments that start with a drive letter, and escape them using a different method. I'm still trying to come up with the bulletproof approach - at this point, I am considering the following:
1) Enclose every argument with " or \ in double quotes
2) Turn every " into "'"'" and every \ into "\" (outer double quotes included). This essentially closes the current " pair, outputs a \ or a "  (surrounded by ' to escape it) then resumes a new " pair.
Once I'm happy with this, I'll email a patch


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