Re: [PATCH 2/2] target/i386: fix IEEE x87 floating-point exception raising

[Peter Maydell]

On Fri, 15 May 2020 at 22:23, Joseph Myers <joseph@codesourcery.com> wrote:
>
> Most x87 instruction implementations fail to raise the expected IEEE
> floating-point exceptions because they do nothing to convert the
> exception state from the softfloat machinery into the exception flags
> in the x87 status word.  There is special-case handling of division to
> raise the divide-by-zero exception, but that handling is itself buggy:
> it raises the exception in inappropriate cases (inf / 0 and nan / 0,
> which should not raise any exceptions, and 0 / 0, which should raise
> "invalid" instead).

> Signed-off-by: Joseph Myers <joseph@codesourcery.com>
> ---
>  target/i386/fpu_helper.c                 | 126 +++-
>  tests/tcg/i386/test-i386-fp-exceptions.c | 831 +++++++++++++++++++++++
>  2 files changed, 926 insertions(+), 31 deletions(-)
>  create mode 100644 tests/tcg/i386/test-i386-fp-exceptions.c

I've just noticed that the new test program here provokes compiler
warnings when 'make check-tcg' builds it:

make[2]: Entering directory
'/home/petmay01/linaro/qemu-for-merges/build/all-linux-static/tests/tcg/i386-linux-user'
/home/petmay01/linaro/qemu-for-merges/tests/docker/docker.py --engine
auto cc --cc gcc -i qemu/fedora-i386-cross -s
/home/petmay01/linaro/qemu-for-merges --   -Wall -Werror -O0 -g
-fno-strict-aliasing -m32
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c
-o test-i386-fp-exceptions  -static
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:
Assembler messages:
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:426:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fistp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:433:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fistp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:440:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fistp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:447:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fistp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:454:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fistp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:541:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fisttp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:548:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fisttp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:555:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fisttp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:562:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fisttp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:569:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fisttp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:576:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fisttp'
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-fp-exceptions.c:583:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fisttp'


There's a similar warning also in test-i386.c:

/home/petmay01/linaro/qemu-for-merges/tests/docker/docker.py --engine
auto cc --cc gcc -i qemu/fedora-i386-cross -s
/home/petmay01/linaro/qemu-for-merges --   -Wall -Werror -O0 -g
-fno-strict-aliasing -fno-pie  -static -m32 -o test-i386 \
   /home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386.c
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-code16.S
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386-vm86.S
-lm
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386.c:
Assembler messages:
/home/petmay01/linaro/qemu-for-merges/tests/tcg/i386/test-i386.c:869:
Warning: no instruction mnemonic suffix given and no register
operands; using default for `fist'

They don't make the build fail but it would be nice if we could
make them go away...

thanks
-- PMM