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To: cygwin AT cygwin DOT com
From: Jean-Pierre Flori <jpflori AT gmail DOT com>
Subject: Re: Possibly wrong address passed to callq asm instruction within MPIR test binaries
Date: Mon, 7 Apr 2014 14:02:43 +0000 (UTC)
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References: <20140402090750 DOT GP2508 AT calimero DOT vinschen DOT de>	<lhsctu$56e$1 AT ger DOT gmane DOT org> <20140407084312 DOT GA2061 AT calimero DOT vinschen DOT de>	<lhtqa1$ie3$1 AT ger DOT gmane DOT org> <lhtsb6$ie3$2 AT ger DOT gmane DOT org>	<lhtve5$ie3$4 AT ger DOT gmane DOT org> <lhtvgh$ie3$5 AT ger DOT gmane DOT org>	<lhu212$ie3$6 AT ger DOT gmane DOT org> <20140407113027 DOT GA30595 AT calimero DOT vinschen DOT de>	<lhu3dq$ie3$7 AT ger DOT gmane DOT org> <20140407115730 DOT GA721 AT calimero DOT vinschen DOT de>	<lhu95j$ie3$8 AT ger DOT gmane DOT org>
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Le Mon, 07 Apr 2014 13:28:19 +0000, Jean-Pierre Flori a écrit :

> Le Mon, 07 Apr 2014 13:57:30 +0200, Corinna Vinschen a écrit :
> 
>> On Apr  7 11:50, Jean-Pierre Flori wrote:
>>> Le Mon, 07 Apr 2014 13:30:27 +0200, Corinna Vinschen a écrit :
>>> > 
>>> > I'm sorry, but I don't know how this works exactly.  The nm prefix
>>> > is only added for external references, not for inlined functions,
>>> > but I don't know the gory details.  You may be better off to ask on
>>> > the gcc mailing list.
>>> > 
>>> No problem, I've already learned tons of stuff thanks to your help.
>>> I've just posted on gcc-help.
>>> http://gcc.gnu.org/ml/gcc-help/2014-04/msg00024.html
>> 
>> Thanks.  A simple testcase would still be nice, of course.
>> 
>> 
> Sure, but it seems the issue is that I cannot get the __nm_ prefix when
> I elaborate on a minimal problem like you did.
> 
> I'll still try to get something this afternoon.
I think I got something:
$ cat > lib.c <<EOF
#include <stdio.h>

int
foo (int a)
{
  printf ("a = %d\n", a);
  return a;
}
EOF
$cat > asm.as <<EOF
global nothing
;export nothing
nothing:
  ret
  end
EOF
$ cat > app.c <<EOF
#include <stdio.h>

extern int foo (int);

int
main ()
{
  int x = foo (42);
  printf ("x = %d\n", x);
  nothing();
  return 0;
}
EOF
$ gcc -g -c lib.c -o lib.o
$ yasm -fx64 asm.as -o asm.o
$ gcc -shared lib.o ams.o -Wl,--out-implib=lib.dll.a -Wl,--export-all-
symbols -o lib.dll
$ gcc -g -o app app.c -L. -llib
$ ./app
...
<segfault>

Without the export directive (commented above) I get __nm_ prefix and 
wrong callq instruction.
With it, the __nm_prefix disappears and the trampoline correctly used.


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