Subject: Re: bug#57849: 29.0.50; MacOS ld warning from native compilation

From: Gerd Möllmann <[email-masked]>
Date: Sat, 17 Sep 2022 09:16:20 +0200

Gerd Möllmann <[email-masked]> writes:

> Andrea Corallo <[email-masked]> writes:
>
>> Gerd Möllmann <[email-masked]> writes:
>
>>> I'm not sure this is true for elns.  What if a function in a.eln calls a
>>> function F in b.eln?
>>
>> This is never the case. Functions in .eln files either call functions in
>> Emacs core or either call functions in the same .eln file.
>
> Thanks, good to know.
>
> I'll give it a spin with -bundle... later today.

That failed miserably.  What I tried:

(1) See with which options elns are compiled/linked.

(let ((native-comp-driver-options '("-v")))
  (native-compile "/Users/gerd/emacs/crash.el"))

gives an output ending with

 /opt/homebrew/Cellar/gcc/12.2.0/bin/../libexec/gcc/aarch64-apple-darwin21/12/collect2 -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX12.sdk/ -dynamic -arch arm64 -macosx_version_min 12.0.0 -o /var/folders/1d/k_6t25f94sl83szqbf8gpkrh0000gn/T//libgccjit-YMST3m/fake.so -L/opt/homebrew/Cellar/gcc/12.2.0/bin/../lib/gcc/current/gcc/aarch64-apple-darwin21/12 -L/opt/homebrew/Cellar/gcc/12.2.0/bin/../lib/gcc/current/gcc -L/opt/homebrew/Cellar/gcc/12.2.0/bin/../lib/gcc/current/gcc/aarch64-apple-darwin21/12/../../.. /var/folders/1d/k_6t25f94sl83szqbf8gpkrh0000gn/T//ccbfcNDH.o -undefined dynamic_lookup -dylib -dylib_install_name crash-e892b236-cea0f727.eln -lemutls_w -lgcc -lSystem -lgcc -no_compact_unwind -rpath @loader_path -rpath /opt/homebrew/Cellar/gcc/12.2.0/lib/gcc/current/gcc/aarch64-apple-darwin21/12 -rpath /opt/homebrew/Cellar/gcc/12.2.0/lib/gcc/current/gcc -rpath /opt/homebrew/Cellar/gcc/12.2.0/lib/gcc/current
ld: warning: -undefined dynamic_lookup may not work with chained fixups

That is, it builds a shared object (-dynamic).

(2) -bundle_loader requires -bundle.  Ld gives an error if
-bundle_loader is used without -bundle.  A "bundle" in Mach-O, which is
what MacOS is using instead of ELF, say, is something different than a
shared library.  Example:

gcc -v -o eln.dylib -twolevel_namespace -undefined dynamic_lookup -dylib -bundle_loader hansi eln.c
ld: -bundle_loader can only be used with -bundle

(3) Tried to add -bundle like this

(let ((native-comp-driver-options '("-v" "-bundle")))
  (native-compile "/Users/gerd/emacs/crash.el"))

but it fails

Compiling /Users/gerd/.emacs.d/eln-cache/29_0_50-72ec8db5/crash-e892b236-cea0f727.eln...
Using built-in specs.
aarch64-apple-darwin21-gcc-12: error: -bundle not allowed with -dynamiclib
COLLECT_GCC=aarch64-apple-darwin21-gcc-12

I odn't know how to remove the -dynamic from (1).

As an aside, -bundler_loader actually requires an argument <executable>,
which would be Emacs in our case.  What that means for Emacs' build
process is unclear to me, but it doesn't feel good.

So, I declare this a complete failure.

Anyone with an idea what else to try?  Otherwise my proposal is to
either add something to etc/PROBLEMS describing how to add "-Wl,-w", or
add that option by default on Darwin.

I didn't check if emacs-28 has the same problem, but I don't see why it
wouldn't.

If we add -Wl by default, an open question is if -w is supported on all
all versions of MacOS that Emacs supports, which I can't find a definite
answer to.