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Date: Sat, 25 Oct 2025 21:12:47 +0900
To: cygwin AT cygwin DOT com
Cc: Thomas Huth <th DOT huth AT posteo DOT eu>
Subject: Re: Problem with the SDL2 package in Cygwin
Message-Id: <20251025211247.602c8d8916cffdfc8ac645e6@nifty.ne.jp>
In-Reply-To: <20251011205113.0d09ca46@tpx1>
References: <20251011205113 DOT 0d09ca46 AT tpx1>
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From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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On Sat, 11 Oct 2025 18:51:14 +0000
Thomas Huth wrote:
> 
>  Hi!
> 
> In the Hatari project (www.hatari-emu.org), we recently hit a problem in the
> CI when we compile Hatari with Cygwin. A couple of weeks ago, everything
> was working still fine:
> 
>  https://cirrus-ci.com/task/4681700988420096
> 
> Then it suddenly started failing - also for the very same code level of
> Hatari that was working fine before:
> 
>  https://cirrus-ci.com/task/6377222543507456
> 
> The only difference was that the SDL2 package of Cygwin recently has been
> upgraded from 2.32.8-1 to 2.32.56-1.
> 
> Christian Zietz, a user of Hatari who has a Windows installation (I don't)
> debugged the issue a little bit and concluded that it's crashing somewhere
> during exit():
> 
>  https://sourceforge.net/p/hatari/mailman/hatari-devel/thread/00253a75-4089-4d8a-846e-8d5c0a4899ee%40gmx.net/#msg59242465
> 
> He reproduced it with the following small test program:
> 
> --------------------- 8< ----------------------------------------
> 
> WDAGUtilityAccount AT 9f56fa41-fdda-4d08-96da-76c506c9465a /tmp/sdltest
> $ cat sdltest.c
> #include <stdio.h>
> #include <SDL.h>
> 
> int main(int arc, char ** argv) {
> 
>     if (SDL_Init( SDL_INIT_VIDEO ) == 0) {
> 
>         printf("SDL_Init succeeded\n");
>         printf("Calling SDL_Quit()\n");
>         SDL_Quit();
>     }
> 
>     return 0;
> }
> WDAGUtilityAccount AT 9f56fa41-fdda-4d08-96da-76c506c9465a /tmp/sdltest
> $ sdl2-config --version
> 2.32.56
> 
> WDAGUtilityAccount AT 9f56fa41-fdda-4d08-96da-76c506c9465a /tmp/sdltest
> $ gcc -g -O1 -o sdltest sdltest.c -I /usr/include/SDL2/ -lsdl2
> 
> WDAGUtilityAccount AT 9f56fa41-fdda-4d08-96da-76c506c9465a /tmp/sdltest
> $ ./sdltest
> SDL_Init succeeded
> Calling SDL_Quit()
> 
> WDAGUtilityAccount AT 9f56fa41-fdda-4d08-96da-76c506c9465a /tmp/sdltest
> $ ./sdltest > out.txt
> 
> WDAGUtilityAccount AT 9f56fa41-fdda-4d08-96da-76c506c9465a /tmp/sdltest
> $ cat out.txt
> 
> WDAGUtilityAccount AT 9f56fa41-fdda-4d08-96da-76c506c9465a /tmp/sdltest
> $ gdb sdltest.exe
> GNU gdb (GDB) (Cygwin 14.2-1) 14.2
> Copyright (C) 2023 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.
> Type "show copying" and "show warranty" for details.
> This GDB was configured as "x86_64-pc-cygwin".
> Type "show configuration" for configuration details.
> For bug reporting instructions, please see:
> <https://www.gnu.org/software/gdb/bugs/>.
> Find the GDB manual and other documentation resources online at:
>     <http://www.gnu.org/software/gdb/documentation/>.
> 
> For help, type "help".
> Type "apropos word" to search for commands related to "word"...
> Reading symbols from sdltest.exe...
> (gdb) run
> Starting program: /tmp/sdltest/sdltest.exe
> [New Thread 7024.0x1918]
> [New Thread 7024.0x1210]
> [New Thread 7024.0x1a80]
> [New Thread 7024.0x18d0]
> SDL_Init succeeded
> Calling SDL_Quit()
> 
> Thread 1 "sdltest" received signal SIGSEGV, Segmentation fault.
> 0x00000003f96f1020 in ?? ()
> (gdb) bt
> #0  0x00000003f96f1020 in ?? ()
> #1  0x00007ffb2a577a63 in __call_exitprocs (code=code AT entry=0, d=d AT entry=0x0)
>     at /usr/src/debug/cygwin-3.6.4-1/newlib/libc/stdlib/__call_atexit.c:123
> #2  0x00007ffb2a5356ce in exit (code=0) at /usr/src/debug/cygwin-3.6.4-1/newlib/libc/stdlib/exit.c:60
> #3  0x00007ffb2a3d6a98 in cygwin_exit (n=0) at /usr/src/debug/cygwin-3.6.4-1/winsup/cygwin/dcrt0.cc:1238
> #4  0x00007ffb2a3d80d4 in dll_crt0_1 () at /usr/src/debug/cygwin-3.6.4-1/winsup/cygwin/dcrt0.cc:1003
> #5  0x00007ffb2a3d5d05 in _cygtls::call2 (this=0x7ffffce00, func=0x7ffb2a3d707c <dll_crt0_1(void*)>, arg=0x0,
>     buf=buf AT entry=0x7ffffcdf0) at /usr/src/debug/cygwin-3.6.4-1/winsup/cygwin/cygtls.cc:41
> #6  0x00007ffb2a3d5dbb in _cygtls::call (func=<optimized out>, arg=<optimized out>)
>     at /usr/src/debug/cygwin-3.6.4-1/winsup/cygwin/cygtls.cc:28
> #7  0x0000000000000000 in ?? ()
> (gdb)
> 
> --------------------- 8< ----------------------------------------
> 
> Could someone please have a look?

Thanks for the report.

I looked into this problem, and found this issue is not a bug of
SDL2/SDL3 package.

Attached simple test case also reproduces the same issue.

I also found the following patch against cygwin1.dll resolves
the issue. I'll submit the patch to cygwin-patches mailing list
after aome more review by myself.

diff --git a/winsup/cygwin/dll_init.cc b/winsup/cygwin/dll_init.cc
index 1369165c9..42ee73c79 100644
--- a/winsup/cygwin/dll_init.cc
+++ b/winsup/cygwin/dll_init.cc
@@ -584,7 +584,8 @@ dll_list::detach (void *retaddr)
 	  /* Ensure our exception handler is enabled for destructors */
 	  exception protect;
 	  /* Call finalize function if we are not already exiting */
-	  if (!exit_state)
+	  /* Loaded DLLs need finalize function even in the exiting state */
+	  if (!exit_state || d->type == DLL_LOAD)
 	    __cxa_finalize (d->handle);
 	  d->run_dtors ();
 	}
@@ -609,9 +610,10 @@ dll_list::init ()
   /* Walk the dll chain, initializing each dll */
   dll *d = &start;
   dll_global_dtors_recorded = d->next != NULL;
-  /* Init linked and early loaded Cygwin DLLs. */
+  /* Init linked Cygwin DLLs. As for loaded DLLs, dll::init() is already
+     called from dlopen(). */
   while ((d = d->next))
-    if (d->type == DLL_LINK || d->type == DLL_LOAD)
+    if (d->type == DLL_LINK)
       d->init ();
 }
 

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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#include <stdio.h>
#include <dlfcn.h>
static void *dll3;
static void dllinit(void) __attribute__((constructor));
static void dllinit(void)
{
	printf("+++++++++++++++++++++++++++++\n");
	dll3 = dlopen("dll3.dll", RTLD_LOCAL|RTLD_NOW);
}
static void dllquit(void) __attribute__((destructor));
static void dllquit(void)
{
	printf("-----------------------------\n");
	dlclose(dll3);
}
void func2()
{
}

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#include <stdio.h>
static void dllinit(void) __attribute__((constructor));
static void dllinit(void)
{
	printf("++++++++++++++\n");
}
static void dllquit(void) __attribute__((destructor));
static void dllquit(void)
{
	printf("--------------\n");
}
void func3()
{
}

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extern void func2();
int main()
{
	func2();
	return 0;
}

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