[squid-dev] [PATCH] Fix libatomic detection

[Kinkie]

On Mon, Jan 4, 2016 at 6:47 AM, Amos Jeffries <squid3 at treenet.co.nz> wrote:
> On 28/12/2015 10:25 p.m., Kinkie wrote:
>> Hi,
>>
>> On Mon, Dec 28, 2015 at 1:32 AM, Amos Jeffries wrote:
>>> On 24/12/2015 11:32 a.m., Kinkie wrote:
>>>> Hi,
>>>>   libatomic detection is currently broken in configure.ac; it will
>>>> define -latomic even in case where it wouldn't be required (e.g.
>>>> because it's already provided by the compiler).
>>>> The attached patch fixes the broken case. Unfortunately I don't know a
>>>> system where this library is required, I'm convinced there's room for
>>>> further simplification.
>>>
>>> It was for Clang builds IIRC. At least 3.5 needs it added.
>>>
>>> Does this work instead for shorter code?
>>>   AC_SEARCH_LIBS([__atomic_load_8],[atomic],[
>>>     ATOMICLIB="$ac_cv_search___atomic_load_8"
>>>   ],[])
>>
>> unfortunately not, as the result could be "none required" or "no",
>> too. The former is actually the error case which bought me to the
>> topic.
>> Documentation states that if a library is needed it should get
>> automatically added to LIBS though.
>
> "Unless the 3rd and 4th parameters are specified". So it will be
> automatically added under your patch, but not under the existing/older code.
>
> Which was an intentional omission from LIBS to avoid build warnings on
> some distros about unnecessary dependencies being linked in (such as
> <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=770928>). Since most
> of the helper binaries do not use atomics (yet, though we could thread
> them in future) the -latomic addition is only needed by squid_LDADD not
> the generic LIBS / LDADD.
>
> Amos
>

Are you sure? This from the doc I could find:
===
the default action-if-found code, adding the library to the LIBS
variables, is always executed, even if a parameter is passed
===

I have no objection on the intention, of course.
If you are right, then the one-liner below should then do the trick.
If I am right, we need to go through the
SQUID_SAVE_STATE/SQUID_ROLLBACK_STATE dance on top of that.

=== modified file 'configure.ac'
--- configure.ac    2016-01-04 14:39:06 +0000
+++ configure.ac    2016-01-04 18:25:48 +0000
@@ -458,7 +458,7 @@
 fi

 ## check for atomics library before anything that might need it
-AC_SEARCH_LIBS([__atomic_load_8],[atomic])
+AC_SEARCH_LIBS([__atomic_load_8],[atomic],[],[])
 if test "x$ac_cv_search___atomic_load_8" = "-latomic"; then
   ATOMICLIB="-latomic"
 fi



-- 
    Francesco