[PATCH] Cygwin: syscalls.cc: remove ".dll" from, blessed_executable_suffixes

Ken Brown kbrown@cornell.edu
Thu Aug 4 12:00:32 GMT 2022

Patch attached.  I'm not 100% sure of this since it does change behavior (but in 
a weird case).

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From 97a2fc0d07c8f9045b73716ac5a05f972d5bd75c Mon Sep 17 00:00:00 2001
From: Ken Brown <kbrown@cornell.edu>
Date: Wed, 3 Aug 2022 16:45:23 -0400
Subject: [PATCH] Cygwin: syscalls.cc: remove ".dll" from

This reverts commit d9e9c7b5a7.  The latter added ".dll" to the
blessed_executable_suffixes array because on 32-bit Windows, the
GetBinaryType function would report that a 64-bit DLL is an
executable, contrary to the documentation of that function.

That anomaly does not exist on 64-bit Windows, so we can remove ".dll"
from the list.  Reverting the commit does, however, change the
behavior of the rename(2) syscall in the following unlikely situation:
Suppose we have an executable foo.exe and we make the call

  rename ("foo", "bar.dll");

Previously, foo.exe would be renamed to bar.dll.  So bar.dll would
then be an executable without the .exe extension.  The new behavior is
that foo.exe will be renamed to bar.dll.exe.  [Exception: If there
already existed an executable (not a DLL!) with the name bar.dll, then
.exe will not be appended.]
 winsup/cygwin/globals.cc  | 1 -
 winsup/cygwin/syscalls.cc | 6 ------
 2 files changed, 7 deletions(-)

diff --git a/winsup/cygwin/globals.cc b/winsup/cygwin/globals.cc
index e8147cb5c..e909d0f8f 100644
--- a/winsup/cygwin/globals.cc
+++ b/winsup/cygwin/globals.cc
@@ -120,7 +120,6 @@ const int __collate_load_error = 0;
   extern UNICODE_STRING _RDATA ro_u_empty = _ROU (L"");
   extern UNICODE_STRING _RDATA ro_u_lnk = _ROU (L".lnk");
   extern UNICODE_STRING _RDATA ro_u_exe = _ROU (L".exe");
-  extern UNICODE_STRING _RDATA ro_u_dll = _ROU (L".dll");
   extern UNICODE_STRING _RDATA ro_u_com = _ROU (L".com");
   extern UNICODE_STRING _RDATA ro_u_scr = _ROU (L".scr");
   extern UNICODE_STRING _RDATA ro_u_sys = _ROU (L".sys");
diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
index e6d68cc07..599b2b793 100644
--- a/winsup/cygwin/syscalls.cc
+++ b/winsup/cygwin/syscalls.cc
@@ -2133,12 +2133,6 @@ nt_path_has_executable_suffix (PUNICODE_STRING upath)
   static const PUNICODE_STRING blessed_executable_suffixes[] =
-    &ro_u_dll,	/* Messy, messy.  Per MSDN, the GetBinaryType function is
-		   supposed to return with ERROR_BAD_EXE_FORMAT. if the file
-		   is a DLL.  On 64-bit Windows, this works as expected for
-		   32-bit and 64-bit DLLs.  On 32-bit Windows this only works
-		   for 32-bit DLLs.  For 64-bit DLLs, 32-bit Windows returns
-		   true with the type set to SCS_64BIT_BINARY. */

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