Any success with emacs 2.1.4 under cygwin 1.5.21?

Any success with emacs 2.1.4 under cygwin 1.5.21?

[Sean M. Paus]

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I've recently upgraded my cygwin installation to 1.5.21.  Since then, I
have had no luck getting emacs to run.  I've tried the stock 21.2 that
comes with the cygwin distribution, the test 21.3 that was posted a
while back, and I've even downloaded and (well half) built the latest
sources from the emacs CVS repository.

The problem is that emacs just hangs and takes up gobs of CPU.  I
ultimately tracked this down to a tight infinite loop in
_malloc_internal (gmalloc.c).  For some reason, align (also in
gmalloc.c) is returning a pointer that is smaller than _heapbase.  The
calculation to determine what block the newly requested memory is in
(BLOCK(result+size)) returns a ridiculously huge number.  Since
_malloc_internal incrementally doubles the new size of the heap until
the requested memory fits, at some point the multiplication overflows
and newsize gets a value of 0.  Since 0 * 2 is always zero, the test for
BLOCK(result+size) > newsize will always succeed and _malloc_internal
gets stuck in a tight loop multiplying 0 by 2 forever.

The really strange thing is that, while building emacs, temacs has no
problem running.  Apparently, there's a different mechanism from the
standard sbrk (something called bss_sbrk) that temacs uses to increase
the size of the heap.  However, temacs then "disables" bss_sbrk causing
the standard sbrk to be "re-enabled".  It's at this point that
boostrap_emacs encounters the problem described above.

I can't find anything in the difference between cygwin 1.5.18 and 1.5.21
that might cause this.  It also appears that any support for cygwin has
dried up.

Any thoughts?

Sean


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Re: Any success with emacs 2.1.4 under cygwin 1.5.21?

[Eli Zaretskii]

> Date: Thu, 28 Sep 2006 17:49:52 -0400
> From: "Sean M. Paus" <spaus@pobox.com>
> 
> I've recently upgraded my cygwin installation to 1.5.21.  Since then, I
> have had no luck getting emacs to run.  I've tried the stock 21.2 that
> comes with the cygwin distribution, the test 21.3 that was posted a
> while back, and I've even downloaded and (well half) built the latest
> sources from the emacs CVS repository.
> 
> The problem is that emacs just hangs and takes up gobs of CPU.  I
> ultimately tracked this down to a tight infinite loop in
> _malloc_internal (gmalloc.c).  For some reason, align (also in
> gmalloc.c) is returning a pointer that is smaller than _heapbase.  The
> calculation to determine what block the newly requested memory is in
> (BLOCK(result+size)) returns a ridiculously huge number.  Since
> _malloc_internal incrementally doubles the new size of the heap until
> the requested memory fits, at some point the multiplication overflows
> and newsize gets a value of 0.  Since 0 * 2 is always zero, the test for
> BLOCK(result+size) > newsize will always succeed and _malloc_internal
> gets stuck in a tight loop multiplying 0 by 2 forever.

Thanks for investigating the problem, but this is not a good place to
post such reports.  Please use emacs-devel@gnu.org, since the problem
seems to exist in the CVS code as well (or did I misunderstand?).

Also, you may wish to search the archives of emacs-devel and
emacs-pretest-bug mailing lists, as I think something similar was
reported in the past.

(I myself don't use Cygwin, so I cannot help you more at this time.)