[PATCH] dup2: work around cygwin bug

[Eric Blake]

Detected by './gnulib-tool --test dup2 cloexec'.
Reported upstream: http://cygwin.com/ml/cygwin/2012-12/msg00377.html
and fixed already: http://cygwin.com/ml/cygwin-cvs/2012-q4/msg00202.html
but as we want to work with older cygwin, we'll have to carry this
in gnulib for a while.

* m4/dup2.m4 (gl_FUNC_DUP2): Flush out cygwin core dump.
* lib/dup2.c (rpl_dup2): Work around it.
* doc/posix-functions/dup2.texi (dup2): Document it.

Signed-off-by: Eric Blake <address@hidden>
---

Pushed.

 ChangeLog                     | 7 +++++++
 doc/posix-functions/dup2.texi | 2 +-
 lib/dup2.c                    | 3 +++
 m4/dup2.m4                    | 5 ++++-
 4 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 9d1a69b..af52d73 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2012-12-31  Eric Blake  <address@hidden>
+
+       dup2: work around cygwin bug
+       * m4/dup2.m4 (gl_FUNC_DUP2): Flush out cygwin core dump.
+       * lib/dup2.c (rpl_dup2): Work around it.
+       * doc/posix-functions/dup2.texi (dup2): Document it.
+
 2012-12-30  Paul Eggert  <address@hidden>

        regex: remove unnecessary dependency on localcharset.h
diff --git a/doc/posix-functions/dup2.texi b/doc/posix-functions/dup2.texi
index 012bb7f..14e5236 100644
--- a/doc/posix-functions/dup2.texi
+++ b/doc/posix-functions/dup2.texi
@@ -18,7 +18,7 @@ dup2

 @item
 This function crashes when invoked with invalid arguments on some platforms:
-MSVC 9.
+Cygwin 1.7.17, MSVC 9.

 @item
 This function resets the @code{FD_CLOEXEC} flag when duplicating an fd
diff --git a/lib/dup2.c b/lib/dup2.c
index f6d0f1c..36b3399 100644
--- a/lib/dup2.c
+++ b/lib/dup2.c
@@ -95,7 +95,10 @@ rpl_dup2 (int fd, int desired_fd)
 # ifdef F_GETFL
   /* On Linux kernels 2.6.26-2.6.29, dup2 (fd, fd) returns -EBADF.
      On Cygwin 1.5.x, dup2 (1, 1) returns 0.
+     On Cygwin 1.7.17, dup2 (1, -1) dumps core.
      On Haiku, dup2 (fd, fd) mistakenly clears FD_CLOEXEC.  */
+  if (desired_fd < 0)
+    fd = desired_fd;
   if (fd == desired_fd)
     return fcntl (fd, F_GETFL) == -1 ? -1 : fd;
 # endif
diff --git a/m4/dup2.m4 b/m4/dup2.m4
index fc86e80..fa7f6d5 100644
--- a/m4/dup2.m4
+++ b/m4/dup2.m4
@@ -1,4 +1,4 @@
-#serial 18
+#serial 19
 dnl Copyright (C) 2002, 2005, 2007, 2009-2012 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -39,6 +39,9 @@ AC_DEFUN([gl_FUNC_DUP2],
             /* Many gnulib modules require POSIX conformance of EBADF.  */
             if (dup2 (2, 1000000) == -1 && errno != EBADF)
               result |= 16;
+            /* Flush out a cygwin core dump.  */
+            if (dup2 (2, -1) != -1 || errno != EBADF)
+              result |= 32;
             return result;
            ])
         ],
-- 
1.8.0.2