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etc/PROBLEMS: Describe issues with native compilation on Cygwin

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Ken Brown 2022-07-11 13:03:32 -04:00
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@ -2849,6 +2849,71 @@ please call support for your X-server and see if you can get a fix.
If you do, please send it to bug-gnu-emacs@gnu.org so we can list it here.
* Runtime problems specific to Cygwin
** Fork failures in a build with native compilation
To prevent fork failures, shared libraries on Cygwin need to be
rebased occasionally, for the reasons explained here:
https://cygwin.com/cygwin-ug-net/highlights.html#ov-hi-process-problems
This includes the .eln files produced by an Emacs built with native
compilation.
Rebasing is handled by Cygwin's autorebase postinstall script every
time you run the Cygwin setup program (which you should do with no
Cygwin processes running). This script knows about the .eln files
installed in the standard places (e.g.,
/usr/lib/emacs/28.1/native-lisp), but it does not know about those in
your user cache (e.g., /home/<username>/.emacs.d/eln-cache). In order
for these to be automatically rebased, you must create a file
/var/lib/rebase/userpath.d/<username>
with one line for each directory containing .eln files. If you are
running an installed Emacs, it should suffice to list your cache
directory. For example, if there is an Emacs user "kbrown", then
there should be a file
/var/lib/rebase/userpath.d/kbrown
containing the single line
/home/kbrown/.emacs.d/eln-cache
If you are running an Emacs that you have built but not installed,
then you will need an additional line giving the path to the
native-lisp subdirectory of your build directory.
If more than one user will be using Emacs on your system, there should
be a file like this for each user.
Rebasing is not currently done when new .eln files are created, so
fork failures are still possible between runs of Cygwin's setup
program. If you ever see a fork failure whose error message refers to
a .eln file, you should be able to fix it temporarily by exiting emacs
and issuing the command
find ~/.emacs.d/eln-cache -name '*.eln' | rebase -O -T -
This is called an "ephemeral" rebase. Again, if you are running an
Emacs that has not been installed, you need to add the native-lisp
subdirectory of your build directory to this command. Alternatively,
stop all Cygwin processes and run Cygwin's setup program to let the
autorebase postinstall script run.
It is hoped that the measures above will make native compilation
usable on 64-bit Cygwin, with only an occasional minor annoyance. In
the 32-bit case, however, the limited address space makes frequent
fork failures extremely likely. It is therefore strongly recommended
that you not build Emacs with native compilation on 32-bit Cygwin.
Indeed, the configure script will not allow this unless you use the
--with-cygwin32-native-compilation option.
See bug#50666 for further discussion.
* Runtime problems specific to macOS
** Error message when opening Emacs on macOS