[PATCH 0/3] ARM with only 32-bit floats do not have fast 64-bit FMA

[Sebastian Huber]

On 01/09/2020 19:21, Sebastian Huber wrote:

> On 01/09/2020 18:32, Sebastian Huber wrote:
>
>> Hello,
>>
>> with the latest Newlib, I get a linker error in the RTEMS test suite:
>>
>>
>> undefined reference to `fma'
>> undefined reference to `fmaf'
>>
>> The following machine flags are used:
>>
>> '-march=armv7-a', '-mthumb', '-mfpu=neon', '-mfloat-abi=hard', 
>> '-mtune=cortex-a9'
>>
>> It seems to be missing in the corresponding multilib:
>>
>> nm /build/rtems/6/arm-rtems6/lib/thumb/armv7-a+simd/hard/libm.a | 
>> grep fma
>> lib_a-fmal.o:
>>          U fma
>> 00000000 T fmal
>> lib_a-fmaxl.o:
>>          U fmax
>> 00000000 T fmaxl
>> lib_a-s_fma.o:
>> lib_a-s_fmax.o:
>> 00000000 T fmax
>> lib_a-sf_fma.o:
>> lib_a-sf_fmax.o:
>> 00000000 T fmaxf
>>
> It seems to be present in only some multilibs:
>
> for i in $(find /build/rtems/6/arm-rtems6/lib -name libm.a); do echo 
> $i ; nm --defined-only $i | grep 'T.*\<fma\>'; done
> /build/rtems/6/arm-rtems6/lib/eb/thumb/armv7-r+fp/hard/libm.a
> /build/rtems/6/arm-rtems6/lib/eb/thumb/armv7-r/libm.a
> /build/rtems/6/arm-rtems6/lib/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/cortex-m4/hard/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/cortex-m3/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/cortex-m7/hard/libm.a
> 00000000 T fma
> /build/rtems/6/arm-rtems6/lib/thumb/armv6-m/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/armv7-r+fp/hard/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/armv7-r/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/cortex-m4+nofp/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/armv7-a+simd/hard/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/armv7-a/libm.a
> /build/rtems/6/arm-rtems6/lib/armv5te+fp/hard/libm.a
>
> for i in $(find /build/rtems/6/arm-rtems6/lib -name libm.a); do echo 
> $i ; nm --defined-only $i | grep 'T.*\<fmaf\>'; done
> /build/rtems/6/arm-rtems6/lib/eb/thumb/armv7-r+fp/hard/libm.a
> /build/rtems/6/arm-rtems6/lib/eb/thumb/armv7-r/libm.a
> /build/rtems/6/arm-rtems6/lib/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/cortex-m4/hard/libm.a
> 00000000 T fmaf
> /build/rtems/6/arm-rtems6/lib/thumb/cortex-m3/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/cortex-m7/hard/libm.a
> 00000000 T fmaf
> /build/rtems/6/arm-rtems6/lib/thumb/armv6-m/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/armv7-r+fp/hard/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/armv7-r/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/cortex-m4+nofp/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/armv7-a+simd/hard/libm.a
> /build/rtems/6/arm-rtems6/lib/thumb/armv7-a/libm.a
> /build/rtems/6/arm-rtems6/lib/armv5te+fp/hard/libm.a

I think the problem is somewhere in the build system:

find -name s_fma.c
./newlib/libm/machine/arm/s_fma.c
./newlib/libm/machine/aarch64/s_fma.c
./newlib/libm/machine/riscv/s_fma.c
./newlib/libm/machine/spu/s_fma.c
./newlib/libm/common/s_fma.c

I guess the machine-specific file overrides the common file. If the 
machine-specific file is empty due to pre-processor magic, then the 
default implementation is still not present.