-Qunused-parameter and clang (was Re: GHC Port on 9-CURRENT)

Eric McCorkle eric at shadowsun.net
Tue Jun 28 21:10:01 UTC 2011

On 6/28/11 4:06 PM, Niclas Zeising wrote:
> On 2011-06-28 21:19, Pan Tsu wrote:
>> Niclas Zeising<zeising at daemonic.se>  writes:
>>> Sorry for hijacking this thread, and cross posting.
>>> On 2011-06-26 03:07, Gabor PALI wrote:
>>>>> With Clang, an error occurs in one of the configure scripts, because
>>>>> Clang warns about unused command-line arguments, and the configure
>>>>> script assumes that to be a compiler error.  You can deal with this by
>>>>> adding -Qunused-parameter to CFLAGS.
>>>> Thanks for investigating this.
>>> This should probably be made the default, at least for ports when clang
>>> is compiled, since the output generated when not using
>>> -Qunused-parameter confuses configure scripts, and stops at least
>>> FireFox 5 from compiling, that I know of.
>> Do you use ccache? Try without.
>> For example, the combo confuses libtool
> It has nothing to do with cccache. The issue is that clang by default
> warns when passed flags (-std= -f -W etc.) that's not used during the
> compilation/linking. This can be silenced with -Qunused-arguments, and
> if not, it confuses configure scripts that believe this is an error in
> the code it uses to test for features.
> Regards!

Example: In the GHC port, the configure script tries to figure out 
whether the ISA supports PC-relative indexing.  It does this by 
generating a simple program, which contains some asm containing 
PC-relative indexing, compiling it, and seeing if the compiler generates 
a warning.  If clang warns about unused arguments, then the configure 
script assumes (falsely) that the ISA does not support PC-relative 
indexing, and generates bad assembly code, which causes trouble downstream.

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