Re: Fix for Cygwin/GSlice problem

[Ken Brown <kbrown@cornell.edu>]

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.

Ken