Re: Please revert b2e843161d

> On 25 Jun 2026, at 23:32, Steve Kargl <[email protected]> wrote:
> 
> On 6/25/26 10:57, Andrew Turner wrote:
>>> On 25 Jun 2026, at 17:42, Steve Kargl <[email protected]> wrote:
>>> 
>>> On 6/25/26 01:15, Andrew Turner wrote:
>>>>> On 24 Jun 2026, at 19:58, Steve Kargl <[email protected]> wrote:
>>>>> 
>>>>> Can someone with commit access please revert b2e843161dc3b?
>>>>> 
>>>>>   git log -r b2e843161dc3b79777e873183447c92ed9c3703a
>>>>>   Author: Andrew Turner <[email protected]>
>>>>>   Date:   Tue Nov 2 11:31:17 2021 +0000
>>>>> 
>>>>>   Use a builtin where possible in msun
>>>>> 
>>>>> 
>>>>> If one has a libm built with, e.g., -DUSE_BUILTIN_FMAF,
>>>>> and then tries to debug code that uses fmaf() where the
>>>>> compiler options include -fno-builtin, a segfault
>>>>> occurs.  I suggest purging all of the recent additions
>>>>> of USE_BUILTIN_*.  These are simply not needed as a compiler
>>>>> will use a builtin (if available) instead of a function from
>>>>> libm.
>>>> What architecture and compiler are you using to build libm?
>>>> I only enabled it on arm64 as both llvm and gcc will generate the optimal assembly instruction. Other architectures and compilers the builtin may generate a call to fmaf creating an infinite loop.
>>> 
>>> I'm using
>>> 
>>> % uname -a
>>> FreeBSD hotrats 16.0-CURRENT FreeBSD 16.0-CURRENT #0 main-n284956- de9fe28ab847: Fri Apr 10 10:15:09 PDT 2026 kargl@hotrats:/usr/obj/usr/ src/amd64.amd64/sys/GENERIC amd64
>> I don’t expect it to work on amd64 in the general case. Godbolt shows both GCC and Clang generating an infinite loop jumping to its self [1]. It may work on some architecture levels, however I don’t know enough about amd64 to know if it’s safe to enable.
> 
> Just checked godbolt.  If one uses -O3 -fno-builtin with either gcc
> or clang, the generate assembly includes a call to fmaf in libm.a.
> If you build libm with -DUSE_BUILTIN_FMAF on arm and you use
> -fno-builtin, does the resulting executable seg fault?

I never claimed arm enables it. It is enabled for arm64 as both gcc and clang generate an madd instruction [1].

It looks like it is possible to use it on 32-bit arm when targeting armv8 & using clang however this would only be usable as a combat library as most 32-bit arm hardware supported by the FreeBSD kernel is armv7.

Andrew

[1] https://godbolt.org/z/4rThxM6he
[2] https://godbolt.org/z/fa13bEonP