Subject: Re: [PATCH/RFC v1 1/1] intialize false_but_the_compiler_does_not_know_it_

From: Junio C Hamano <[email-masked]>
Date: Wed, 07 May 2025 09:27:45 -0700

Koji Nakamaru <[email-masked]> writes:

> On Wed, May 7, 2025 at 2:16 AM Junio C Hamano <[email-masked]> wrote:
>> Just for reference (as the proposed log message refers to an "older
>> macOS"), do we know if the toolchain on a more recent release of
>> macOS work without this workaround already?  It may be nice to tell
>> users what version they need to avoid the same issue in their own
>> program.
>
> I tested further with Xcode 14.3.1 (the last version of 14.x) and 15,
> where the former still had the issue and the latter worked without the
> workaround. Xcode 15 introduces a new linker which seems to fix the bug.
>
> cf. https://developer.apple.com/documentation/xcode-release-notes/xcode-15-release-notes#Build-System
>
> Koji Nakamaru

Wonderful.  Thanks for a quick report.

Here is an updated patch with the above information.

Thanks.

--- >8 ---
From: Torsten Bögershausen <[email-masked]>
Date:   Tue May 6 14:06:44 2025 +0200

intialize false_but_the_compiler_does_not_know_it_

Compiling/linking 82e79c63642c on an older MacOs machine (like Xcode
14.3.1, the last version of 14.x series) leads to this:

    Undefined symbols for architecture x86_64:
      "_false_but_the_compiler_does_not_know_it_", referenced from:
          _start_command in libgit.a(run-command.o)

The linker fails to pick up compiler-tricks/not-constant.o that
defines the needed false_but_the_compiler_does_not_know_it_ symbol,
which is the only thing defined in that object file, from the
libgit.a archive.

Initializing the variable explicitly to 0 works around the linker
bug; the symbol type changes from 'C' to 'S' and is picked up by the
linker.

Xcode 15 introduces a new linker, which seems to fix the bug, making
the workaround here unnecessary, and Apple requires [*] to build with
Xcode 16 or later in order to upload to their App Store Connect
since April 24, 2025, but not everybody is expected to upgrade their
toolchain immediately.

 [*] https://developer.apple.com/news/upcoming-requirements/?id=02212025a

Helped-by: Koji Nakamaru <[email-masked]>
Signed-off-by: Torsten Bögershausen <[email-masked]>
[jc: update version info with Koji's help]
Signed-off-by: Junio C Hamano <[email-masked]>

diff --git a/compiler-tricks/not-constant.c b/compiler-tricks/not-constant.c
index 1da3ffc2f5..9fb4f275b1 100644
--- a/compiler-tricks/not-constant.c
+++ b/compiler-tricks/not-constant.c
@@ -1,2 +1,2 @@
 #include <git-compat-util.h>
-int false_but_the_compiler_does_not_know_it_;
+int false_but_the_compiler_does_not_know_it_ = 0;