[Buildroot] [PATCH] toolchain-wrapper: do not use deprecated -mfused-madd

Arnout Vandecappelle arnout at mind.be
Fri Aug 11 21:00:13 UTC 2017



On 11-08-17 19:32, Waldemar Brodkorb wrote:
> Hi,
> Thomas Petazzoni wrote,
> 
>> Hello,
>>
>> On Fri, 11 Aug 2017 07:28:48 +0200, Waldemar Brodkorb wrote:
>>> GCC deprecated -mfused-madd, -ffp-contract=off should
>>> be used for Xburst workaround.
>>> uClibc compilations will fail, because a gcc warning
>>> is emitted while checking for TLS support in the compiler.
>>
>> In which gcc version was -ffp-contract=off added ? Can we use that
>> unconditionally, or is it only available in recent gcc versions ?
> 
> It was added in commit b9be572eda05cd23bbabd6409387d2c7ac782715.
> 
> Not sure how to find when it was added in a release.

$ git describe --contains b9be572eda05cd23bbabd6409387d2c7ac782715
gcc-4_6_0-release~2941

 So we should use something like:

ifeq ($(BR2_TOOLCHAIN_GCC_AT_LEAST_4_6),y)
TOOLCHAIN_WRAPPER_ARGS += -DBR_FP_CONTRACT_OFF
else
TOOLCHAIN_WRAPPER_ARGS += -DBR_NO_FUSED_MADD
endif

 But actually, I'd much prefer this stuff to just be coded in
TOOLCHAIN_WRAPPER_OPTS. But that's a much bigger patch (series) so not for master.

 Regards,
 Arnout


> 4.6.4 seems to have it:
> https://gcc.gnu.org/onlinedocs/gcc-4.6.4/gcc/Optimize-Options.html#index-ffp_002dcontract-691
> 
> I don't find it in earlier release docs.
> 
> best regards
>  Waldemar
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-- 
Arnout Vandecappelle                          arnout at mind be
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