fenv() support broken with GCC 10 on ARM

[Sebastian Huber]

On 09/07/2020 19:16, Eshan Dhawan wrote:

> Hi Sebastian,
> Could you please tell the steps to recreate the error :)

You have to build a GCC 10 for ARM. For example using the latest RTEMS 
Source Builder:

arm-rtems6-gcc --version
arm-rtems6-gcc (GCC) 10.1.1 20200703 (RTEMS 6, RSB 
5ab61d2e8c7ced8c685541509a7ac4eba704e69e, Newlib f095752)
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Then compile the following test program:

#include <fenv.h>

int main()
{
     return fesetenv( FE_DFL_ENV );
}

arm-rtems6-gcc init.c -mthumb -mcpu=cortex-m3 -lm -Wl,-Map,map.txt
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/bin/ld: 
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv-vfp.o):/scratch/git-rtems-source-builder/rtems/build/arm-rtems6-gcc-50666d2-newlib-f095752-x86_64-linux-gnu-1/build/arm-rtems6/thumb/cortex-m3/newlib/targ-include/machine/fenv-softfloat.h:61: 
multiple definition of `__softfloat_float_rounding_mode'; 
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv-softfp.o):/scratch/git-rtems-source-builder/rtems/build/arm-rtems6-gcc-50666d2-newlib-f095752-x86_64-linux-gnu-1/build/arm-rtems6/thumb/cortex-m3/newlib/targ-include/machine/fenv-softfloat.h:61: 
first defined here
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/bin/ld: 
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv-vfp.o):/scratch/git-rtems-source-builder/rtems/build/arm-rtems6-gcc-50666d2-newlib-f095752-x86_64-linux-gnu-1/build/arm-rtems6/thumb/cortex-m3/newlib/targ-include/machine/fenv-softfloat.h:60: 
multiple definition of `__softfloat_float_exception_mask'; 
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv-softfp.o):/scratch/git-rtems-source-builder/rtems/build/arm-rtems6-gcc-50666d2-newlib-f095752-x86_64-linux-gnu-1/build/arm-rtems6/thumb/cortex-m3/newlib/targ-include/machine/fenv-softfloat.h:60: 
first defined here
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/bin/ld: 
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv-vfp.o):/scratch/git-rtems-source-builder/rtems/build/arm-rtems6-gcc-50666d2-newlib-f095752-x86_64-linux-gnu-1/build/arm-rtems6/thumb/cortex-m3/newlib/targ-include/machine/fenv-softfloat.h:59: 
multiple definition of `__softfloat_float_exception_flags'; 
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv-softfp.o):/scratch/git-rtems-source-builder/rtems/build/arm-rtems6-gcc-50666d2-newlib-f095752-x86_64-linux-gnu-1/build/arm-rtems6/thumb/cortex-m3/newlib/targ-include/machine/fenv-softfloat.h:59: 
first defined here
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/bin/ld: 
warning: cannot find entry symbol _start; defaulting to 0000000000008000

In the linker map file you will find this dependency chain:

/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv.o)
                               /tmp/cclZauID.o (fesetenv)
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv-softfp.o)
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv.o) 
(__softfp_feclearexcept)
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv-vfp.o)
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a(lib_a-fenv.o) 
(__vfp_feclearexcept)

You have the following symbols:

nm 
/build/rtems/6/lib/gcc/arm-rtems6/10.1.1/../../../../arm-rtems6/lib/thumb/cortex-m3/libm.a 
--defined-only | grep -C 3 __soft
lib_a-feholdexcept.o:

lib_a-fenv-softfp.o:
00000000 B __softfloat_float_exception_flags
00000000 B __softfloat_float_exception_mask
00000000 B __softfloat_float_rounding_mode
00000000 T __softfp_feclearexcept
00000000 T __softfp_fedisableexcept
00000000 T __softfp_feenableexcept
00000000 T __softfp_fegetenv
00000000 T __softfp_fegetexcept
00000000 T __softfp_fegetexceptflag
00000000 T __softfp_fegetround
00000000 T __softfp_feholdexcept
00000000 T __softfp_feraiseexcept
00000000 T __softfp_fesetenv
00000000 T __softfp_fesetexceptflag
00000000 T __softfp_fesetround
00000000 T __softfp_fetestexcept
00000000 T __softfp_feupdateenv

lib_a-fenv-vfp.o:
00000000 B __softfloat_float_exception_flags
00000000 B __softfloat_float_exception_mask
00000000 B __softfloat_float_rounding_mode
00000000 T __vfp_feclearexcept
00000000 T __vfp_fedisableexcept
00000000 T __vfp_feenableexcept