[newlib-cygwin] Cygwin: execve: fix setting O_APPEND file offset for native child

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=0be0b8f0335ec0fad6188b3570dffeba4ec94fea

commit 0be0b8f0335ec0fad6188b3570dffeba4ec94fea
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Sat Feb 9 15:36:02 2019 +0100

    Cygwin: execve: fix setting O_APPEND file offset for native child
    
    dtable::set_file_pointers_for_exec is called from
    child_info_spawn::worker to move the file position of O_APPEND
    files to EOF if the child is a native child.
    
    However, this only works correctly for the first O_APPEND
    file descriptor:
    
    - set_file_pointers_for_exec calls SetFilePointer.  The higher
      4 bytes of the desired file offset are given to SetFilePointer
      as pointer to a DWORD value.  On return, SetFilePointer returns
      the higher 4 bytes of the new file position in this DWORD.
    
    - So for the second and subsequent descriptors the higher 4 byte
      of the file position depend on what the actual file position
      of the previous file has been set to:
    
    - If the file is > 2 Gigs, the high offset will not be 0 anymore.
    
    - If the desciptor points to a non-seekable file (i.e., a pipe
      or socket), SetFilePosition returns an error and sets the high
      position to -1.
    
    Fix this by calling SetFilePointerEx instead, which does not
    modify the incoming position value.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/dtable.cc   | 5 +++--
 winsup/cygwin/release/3.0 | 3 +++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/dtable.cc b/winsup/cygwin/dtable.cc
index 663f99b..86e0c71 100644
--- a/winsup/cygwin/dtable.cc
+++ b/winsup/cygwin/dtable.cc
@@ -857,12 +857,13 @@ dtable::set_file_pointers_for_exec ()
 {
 /* This is not POSIX-compliant so the function is only called for
    non-Cygwin processes. */
-  LONG off_high = 0;
+  LARGE_INTEGER eof = { QuadPart: 0 };
+
   lock ();
   fhandler_base *fh;
   for (size_t i = 0; i < size; i++)
     if ((fh = fds[i]) != NULL && fh->get_flags () & O_APPEND)
-      SetFilePointer (fh->get_handle (), 0, &off_high, FILE_END);
+      SetFilePointerEx (fh->get_handle (), eof, NULL, FILE_END);
   unlock ();
 }
 
diff --git a/winsup/cygwin/release/3.0 b/winsup/cygwin/release/3.0
index 4cd422a..da0fe09 100644
--- a/winsup/cygwin/release/3.0
+++ b/winsup/cygwin/release/3.0
@@ -100,3 +100,6 @@ Bug Fixes
 
 - Fix exception handling in pthreads.
   Addresses: https://cygwin.com/ml/cygwin/2019-01/msg00149.html
+
+- Fix O_APPEND handling on files when calling non-Cygwin applications
+  Addresses: https://cygwin.com/ml/cygwin/2019-02/msg00081.html