Re: Fix for Cygwin/GSlice problem

[Ken Brown <kbrown@cornell.edu>]

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On 12/9/2009 1:53 PM, Jan Djärv wrote:
> Ken Brown skrev:
>> On 12/9/2009 10:00 AM, Ken Brown wrote:
>>> On 12/9/2009 9:31 AM, Stefan Monnier wrote:
>>>>>>>> +/* Emacs supplies its own malloc, but glib (part of Gtk+) calls
>>>>>>>> + memalign and on Cygwin, that becomes the Cygwin supplied 
>>>>>>>> memalign.
>>>>>>>> + As malloc is not the Cygwin malloc, the Cygwin memalign always
>>>>>>>> + returns ENOSYS. A workaround is to set G_SLICE=always-malloc. */
>>>>>>>> +#define G_SLICE_ALWAYS_MALLOC
>>>>>>> Why does Cygwin-Emacs use its own malloc rather than the system 
>>>>>>> malloc?
>>>>> Emacs prefers its own malloc when the system malloc doesn't have the
>>>>> required hooks.  If this is critical or not I don't know.
>>>>
>>>> I'd suggest we try to use Cygwin's system malloc, with a clear comment
>>>> about why we don't use our own, and what kind of workaround could be
>>>> used (the G_SLICE_ALWAYS_MALLOC) if we wanted to use our own.
>>>
>>> OK, I'll give it a try and report back.  I assume the way to do this 
>>> is to remove '#define G_SLICE_ALWAYS_MALLOC' from src/s/cygwin.h and 
>>> instead #define SYSTEM_MALLOC.  [You don't need to respond unless 
>>> this is wrong.]
>>
>> I tried this, and the build fails with
>>
>> gcc    -o temacs ecrt0.o dispnew.o frame.o scroll.o xdisp.o menu.o 
>> window.o charset.o coding.o category.o ccl.o character.o chartab.o 
>> cm.o term.o terminal.o xfaces.o    emacs.o keyboard.o macros.o 
>> keymap.o sysdep.o buffer.o filelock.o insdel.o marker.o minibuf.o 
>> fileio.o dired.o filemode.o cmds.o casetab.o casefiddle.o indent.o 
>> search.o regex.o undo.o alloc.o data.o doc.o editfns.o callint.o 
>> eval.o floatfns.o fns.o font.o print.o lread.o syntax.o unexcw.o 
>> bytecode.o process.o callproc.o region-cache.o sound.o atimer.o 
>> doprnt.o strftime.o intervals.o textprop.o composite.o md5.o   
>> sheap.o  terminfo.o lastfile.o vm-limit.o  getloadavg.o       -lcurses 
>> -lg   `gcc -print-libgcc-file-name` -lm -lc `gcc -print-libgcc-file-name`
>> vm-limit.o:vm-limit.c:(.text+0x17): undefined reference to 
>> `___after_morecore_hook'
>> vm-limit.o:vm-limit.c:(.text+0x6c): undefined reference to `___morecore'
>>
>> I looked at the source code, and I can't see any place where Cygwin's 
>> malloc.h is getting included.  I don't know if that's the (only) problem.
>>
>> I also asked for help on the Cygwin list and got the following two 
>> responses:
>>
>>> ...cygwin doesn't provide something
>>> that linux does.  It's possible that you may be able to work around
>>> the problem by using a -D__morecore=sbrk (or maybe one more underscore
>>> is needed) on the compile line for vm-limit.c.
>>
>>> why are you bothering to specify the system libs at all?  You're using
>>> the gcc driver to link, it'll do all that for you automatically (and
>>> correctly) if you just leave them out; you shouldn't need anything but
>>> -lcurses out of that lot.  You'll definitely break linking against 
>>> the shared
>>> libgcc by putting the static archive in the list of user libraries 
>>> like that.
>>
>> I'm really in over my head at this point.  If someone sees something I 
>> can do to fix this, I'll give it a try.  Otherwise, maybe we should 
>> just stick with the G_SLICE workaround for now.
>>
> 
> You should be able to just comment out the lines in vm-limit.c, i.e. 
> just put
> 
> void
> memory_warnings (start, warnfun)
>      POINTER start;
>      void (*warnfun) ();
> {
> #ifndef CYGWIN
>  ...
> #endif
> }
> 
> so you can test it.

OK, this enables the compilation to complete, but the resulting emacs
crashes with a segfault, even with G_SLICE=always-malloc.  And disabling
linking against static libgcc doesn't help either.  I think we should
stick with the Emacs malloc and the G_SLICE workaround.

Even though Dave Korn's advice about libraries turned out to be 
irrelevant for this issue, I still think it would be wise to follow it. 
  The attached patch accomplishes this.  Could someone please apply it?

Thanks.

Ken

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--- origsrc/emacs-23.1.90/src/s/cygwin.h	2009-12-08 20:01:43.000000000 -0500
+++ src/emacs-23.1.90/src/s/cygwin.h	2009-12-09 22:11:24.320763600 -0500
@@ -132,6 +132,14 @@ along with GNU Emacs.  If not, see <http
    returns ENOSYS.  A workaround is to set G_SLICE=always-malloc. */
 #define G_SLICE_ALWAYS_MALLOC
 
+/* Don't link against static libgcc */
+#define LIB_GCC
+
+/* Don't list standard libs on link command line */
+#define LIB_STANDARD
+#define LIB_MATH
+#define LIBS_DEBUG
+
 /* the end */
 
 /* arch-tag: 5ae7ba00-83b0-4ab3-806a-3e845779191b