[newlib-cygwin] autload.cc: Avoid clobbering return address in noload on i686

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=859c10beeeaaf1e0a1964118973aca1bc0460a51

commit 859c10beeeaaf1e0a1964118973aca1bc0460a51
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Tue Aug 25 22:15:22 2015 +0200

    autload.cc: Avoid clobbering return address in noload on i686
    
    	This fixes a long-standing problem when GetProcAddress fails
    	to load a function.  The noload code calls SetLastError on
    	i686 without saving the edx register.  Starting with Windows 7,
    	SetLastError apparently uses $edx and the register is set to
    	0x00000000 on return.  So the subsequent `jmp *$edx' in noload
    	supposed to return to the caller, actually jumps to address NULL,
    	which results in a SEGV.
    
            * autoload.cc (noload): i686 only: Save and restore $edx when calling
            SetLastError to avoid clobbering return address stating with Windows 7.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/ChangeLog   | 5 +++++
 winsup/cygwin/autoload.cc | 6 ++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index a23f835..c10d074 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,5 +1,10 @@
 2015-08-25  Corinna Vinschen  <corinna@vinschen.de>
 
+	* autoload.cc (noload): i686 only: Save and restore $edx when calling
+	SetLastError to avoid clobbering return address stating with Windows 7.
+
+2015-08-25  Corinna Vinschen  <corinna@vinschen.de>
+
 	* mmap.cc: Fix a few comments.
 
 2015-08-24  Corinna Vinschen  <corinna@vinschen.de>
diff --git a/winsup/cygwin/autoload.cc b/winsup/cygwin/autoload.cc
index 4299e3a..8f9823b 100644
--- a/winsup/cygwin/autoload.cc
+++ b/winsup/cygwin/autoload.cc
@@ -254,11 +254,13 @@ noload:									\n\
 	addl	%eax,%esp	# Pop off bytes				\n\
 	andl	$0xffff0000,%eax# upper word				\n\
 	subl	%eax,%esp	# adjust for possible return value	\n\
-	pushl	%eax		# Save for later			\n\
+	pushl	%eax		# Save return value for later		\n\
+	pushl	%edx		# Save return address for later		\n\
 	movl	$127,%eax	# ERROR_PROC_NOT_FOUND			\n\
 	pushl	%eax		# First argument			\n\
 	call	_SetLastError@4	# Set it				\n\
-	popl	%eax		# Get back argument			\n\
+	popl	%edx		# Get back return address		\n\
+	popl	%eax		# Get back return value			\n\
 	sarl	$16,%eax	# return value in high order word	\n\
 	jmp	*%edx		# Return				\n\
 1:									\n\