Re: Merging feature/android

[Paul Eggert <eggert@cs.ucla.edu>]

On 2023-03-04 19:16, Po Lu wrote:
> Paul Eggert <eggert@cs.ucla.edu> writes:
> 
>> Actually dynamic module support should build with Sun C 5.15 (i.e.,
>> Oracle Solaris Studio 12.6), because Sun C supports GNU C's
>> __attribute__ ((cleanup)) extension. I think icc also supports that
>> extension. Not that I've ever used modules on those platforms.
> 
> Well, I do recall /opt/SUNwspro/bin/cc choking on emacs-module.c at some
> point in the past.

That's likely an earlier version of Sun C that does not support 
__attribute__ ((cleanup)). I doubt whether it's worth worrying about 
these older Sun C versions. People can get an up-to-date compiler, or 
(better yet) use GCC. It's not worth our time to port to obsolete Sun C.


> the correct solution is to check whether or not the compiler
> supports such an extension, and disable dynamic module support should it
> not.  Which is why we use configure in the first place, instead of
> performing ``checks'' with `GNUC_PREREQ'.

Emacs uses HAS_ATTRIBUTE, which should use Clang's __has_attribute, 
which should work with a recent-enough Android NDK (as these are based 
on Clang).

If you're using an older Android NDK based on GCC, yes that does use 
GNUC_PREREQ, but again this should work unless the older Android NDKs 
are squirrelly about GCC version numbers (are they?).

It's true that the Autoconf Way is to write a little program to test for 
__attribute__((cleanup)) directly, and that may be a good way to go. 
However, I would suggest first understanding why the current approach 
does not work. (But please see below; perhaps we don't need to worry 
about this at all.)


> r21 and r25 are free of this illness, but they don't support old
> versions of Android that Emacs does, such as Android 4.4 or 2.2.
> 
>    (And the other day someone asked me for a build of Emacs that runs on
>     Android 4.1, so these versions are evidently being used.)

Although I'm sure that ancient Android versions are still used 
somewhere, I suggest that we not worry about porting to Android versions 
so old that Google itself no longer supports them. This is the general 
guideline we've used for most other ports, and it should be a good 
guideline for Android too. We have limited development resources and 
it's generally not worth our time to port to an OS if it's not even 
worth the OS maintainer's time to support the OS.

Plus, Emacs is likely to have known security holes if we try to port it 
to no-longer-supported Android, and that would be bad for our users and 
bad publicity for Emacs. Android is one of the biggest malware targets 
out there.


> The attribute leads to a compiler error generating while generating
> debug information

If this Android NDK is so old that Google no longer supports it, I 
wouldn't worry about it. If not, perhaps we'll need to build Emacs 
without the debug-info option that is making that buggy compiler crash.