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Message-ID: <51F0E39C.1090500@dancol.org>
Date: Thu, 25 Jul 2013 01:36:44 -0700
From: Daniel Colascione <dancol@dancol.org>
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To: cygwin@cygwin.com
Subject: Re: python aborts
References: <d0191e464b44f772f988b2050cda4ac8@denis-excoffier.org> <20130522123148.GW2406@calimero.vinschen.de> <51F0CBD2.2030502@dancol.org> <51F0CF92.60009@dancol.org>
In-Reply-To: <51F0CF92.60009@dancol.org>
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On 7/25/2013 12:11 AM, Daniel Colascione wrote:
> On 7/24/2013 11:55 PM, Daniel Colascione wrote:
>> Does that help at all?  I only started seeing this problem after I recom=
piled
>> _wp.dll using gcc 4.7.3.
>=20
> Actually, this problem looks a lot like
> http://www.mail-archive.com/gcc@gcc.gnu.org/msg68316.html: neither Python=
 nor
> _wp links dynamically to libgcc, but cygsqlite3-0.dll does.
>=20

And this is a very nasty bug; Eli's analysis is correct. Say we have module=
s Foo
and Bar. Foo links against shared libgcc, but Bar does not. Now, if we load=
 Foo,
load Bar, unload Foo, then unload Bar, then Foo's initialization code finds
libgcc and registers itself with it, but Foo's deinitializaton code doesn't=
 find
libgcc, tries to instead unregister with Foo's internal data structures, fi=
nds
them uninitialized, and aborts. No wonder changing Python module order arou=
nd
makes the problem go away for a little while.

The right fix for libgcc looks something like this:

--- config/i386/cygming-crtbegin.c.orig 2013-07-25 00:07:35.000000000 -0800
+++ config/i386/cygming-crtbegin.c      2013-07-25 00:33:11.000000000 -0800
@@ -82,6 +82,8 @@
 extern void __gcc_register_frame (void);
 extern void __gcc_deregister_frame (void);

+static HANDLE libgcc_dll;
+
 void
 __gcc_register_frame (void)
 {
@@ -94,8 +96,11 @@
   void (*register_frame_fn) (const void *, struct object *);
   HANDLE h =3D GetModuleHandle (LIBGCC_SONAME);
   if (h)
-    register_frame_fn =3D (void (*) (const void *, struct object *))
-                       GetProcAddress (h, "__register_frame_info");
+    {
+      libgcc_dll =3D LoadLibrary (LIBGCC_SONAME); /* Hold reference */
+      register_frame_fn =3D (void (*) (const void *, struct object *))
+       GetProcAddress (h, "__register_frame_info");
+    }
   else
     register_frame_fn =3D __register_frame_info;
   if (register_frame_fn)
@@ -124,13 +129,16 @@
 {
 #if DWARF2_UNWIND_INFO
   void *  (*deregister_frame_fn) (const void *);
-  HANDLE h =3D GetModuleHandle (LIBGCC_SONAME);
-  if (h)
+  if (libgcc_dll)
     deregister_frame_fn =3D (void* (*) (const void *))
-                         GetProcAddress (libgcc_dl, "__deregister_frame_in=
fo");
+      GetProcAddress (libgcc_dll, "__deregister_frame_info");
   else
     deregister_frame_fn =3D __deregister_frame_info;
   if (deregister_frame_fn)
      deregister_frame_fn (__EH_FRAME_BEGIN__);
+
+  if (libgcc_dll)
+    FreeLibrary (libgcc_dll);
+
 #endif

The problem is that this code is baked into every module compiled with the =
buggy
libgcc. You have to recompile the world to fix it for good --- except if sh=
ared
libgcc is pinned in memory.


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