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Message-ID:	<53BAA770.7070005@dronecode.org.uk>
Date:	Mon, 07 Jul 2014 14:58:08 +0100
From:	Jon TURNEY <jon DOT turney AT dronecode DOT org DOT uk>
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To:	cygwin AT cygwin DOT com
Subject:	Re: abort during exit() with a dynamically loaded C++ library
References:	<53A084E7 DOT 9010807 AT dronecode DOT org DOT uk>
In-Reply-To:	<53A084E7.9010807@dronecode.org.uk>

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On 17/06/2014 19:11, Jon TURNEY wrote:
> I think I have found a problem when building programs using the latest
> mesa library, where abort is being called during exit()
>
> This seems to be x86 specific, and looks like it is somehow related to
> having a C++ library dynamically loaded by a C program.
>
> I think I have reduced it to the following test case:

So, this seems to be related to this patch [1], to fix a different abort 
during __gcc_deregister_frame()

[1] https://sourceware.org/ml/cygwin/2013-07/msg00528.html

Since this code is baked into libgcc itself, that patch has the 
side-effect of making libgcc pin itself in memory.

I can't really tell from what's written there if that was deliberate or 
not, but it seems that it introduces a different problem when the 
executable doesn't have a dependency on libgcc.

> test.c:
>
> #include <assert.h>
> #include <dlfcn.h>
>
> int main()
> {
>     void *h = dlopen("dllib.dll", 0);
>     assert(h);
>     dlclose(h);

The problem can be worked around by adding code to force libgcc to get 
unloaded here, which seems to support this theory, e.g.

+#define LIBGCC_SONAME "cyggcc_s-1.dll"
+   HANDLE hmod_libgcc = GetModuleHandle(LIBGCC_SONAME);
+   FreeLibrary(hmod_libgcc);

> }

Attached is a patch which modifies __gcc_register_frame() to avoid it 
pinning itself in memory.

Alternatively, as one of the emails in the linked thread says [2], the 
assert in __deregister_frame_info_bases() itself could be removed.

[2] http://www.mail-archive.com/gcc AT gcc DOT gnu DOT org/msg68286.html


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