Re: [PATCH v3] cache.h: auto-detect if zlib has uncompress2()

From: Beat Bolli <dev+git@drbeat.li>
Date: Jan 23, 2022, 00:19 UTC
Message-ID: <74d35354-20a6-9cc1-3452-573460c694bd@drbeat.li>
In-Reply-To: <xmqqr190ekrh.fsf@gitster.g>

On 22.01.22 00:23, Junio C Hamano wrote:

Show 12 quoted lines

> Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:
> 
>> As noted in the updated commit message this approach of having an
>> object just for this fallback function comes at the cost of some
>> complexity, but now the compat object lives neatly in its own object.
> 
> I do not see any change in this patch adding costly complexity, but
> I notice lack of one possible trick that might become problem with
> some compilers and linkers when their zlib has uncompress2()
> function.  Let's have this graduate very early in the next cycle, to
> see if anybody on a rarer system sees a complaint due to having to
> deal with a totally empty object file.

OpenSSL has a macro in include/openssl/macros.h to counteract exactly this:

     /*
      * Sometimes OPENSSL_NO_xxx ends up with an empty file and some 
compilers
      * don't like that.  This will hopefully silence them.
      */
     #define NON_EMPTY_TRANSLATION_UNIT static void *dummy = &dummy;

They insert it in the otherwise empty "#else" branch of conditionally complied code.

Cheers, Beat