fenv.h fixes for softfloat

[Ian Lepore]

On Sun, 2012-01-08 at 13:36 -0500, David Schultz wrote:
> The patch below should make the fenv.h functions work on ARM chips
> without an FPU.  (Hardware FPU support is missing anyway, and
> what's in fenv.h right now is probably wrong.)
> 
> It would be great if someone could test this, because I don't have
> the hardware.  The regression tests in tools/regression/lib/msun,
> particularly test-fenv.c, should provide some idea of what's
> working and what isn't.

Right now the most recent FreeBSD version I can conveniently build and
test with on ARM is 8.2.  Your patches applied cleanly to that code.

The compiler whined about missing definition of __fenv_static, so I
added "#define __fenv_static static" in arm/fenv.h, that allowed the
library compile to complete.

My hardware is an Atmel at91rm9200 (180mhz armv4, no fpu).

I'm using this compiler:
  # gcc -v 
  Using built-in specs.
  Target: arm-undermydesk-freebsd
  Configured with: FreeBSD/arm system compiler
  Thread model: posix
  gcc version 4.2.2 20070831 prerelease [FreeBSD]

Building the test with this command in tools/regression/lib/msun:
  cc -pipe -O0 test-fenv.c -o test-fenv -static -lm

Which results in this file:
  # file test-fenv                                                                                
  test-fenv: ELF 32-bit LSB executable, ARM, version 1 (FreeBSD), statically linked, for FreeBSD 8.2 (802508), not stripped

Here's a run with the stock/unpatched 8.2 math lib:
  tflex# /tmp/test-fenv
  1..8
  ok 1 - fenv
  Assertion failed: (fetestexcept(std_except_sets[i]) == 0), function test_fetestclearexcept, file test-fenv.c, line 150.
  Abort (core dumped)

And here with your patches applied:
  tflex# /tmp/test-fenv
  1..8
  ok 1 - fenv
  ok 2 - fenv
  Assertion failed: (fetestexcept(ALL_STD_EXCEPT) == (ALL_STD_EXCEPT ^ excepts)), function test_fegsetexceptflag, file test-fenv.c, line 193.
  Abort (core dumped)

That looks like progress, if not complete success. :)

My first attempts at this yesterday yielded confusing results. I had
copied test-fenv.c into our product-build environment for convenience,
and I forgot that environment puts -DNDEBUG on the command line by
default.  Man, does that ever lead to confusing output... lots of tests
that didn't work appeared to, then test 6 appeared to fail in a
completely confusing way (well, confusing until I realized all those
asserts in the source expanded to nothing).  Given how heavily the test
suite code relies on assert() expanding to actual code, it might not be
a bad idea to put something in each test-whatever.c along the lines of

  #ifdef NDEBUG
  #error This code will not work with NDEBUG defined
  #endif

Now that I've gotten past the workflow-glitches it'll be easy for me to
re-test a new patch or generate more info for you.

-- Ian