Re: [PATCH 0/5] target/i386: fxtract, fscale fixes

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Cc'ing FPU emulation maintainers too.

On 5/7/20 2:42 AM, Joseph Myers wrote:
> Among the various bugs in the x87 floating-point emulation that show
> up through a combination of glibc testing and code inspection, there
> are several in the implementations of the fxtract and fscale
> instructions.  This series fixes those bugs.
> 
> Bugs in other instructions, and bugs relating to floating-point
> exceptions and flag setting, will be addressed separately.  In
> particular, while some of these patches add code that sets exception
> flags in the softfloat state, it's generally the case that the x87
> emulation ignores exceptions in that state rather than propagating
> them to the status word (and to generating traps where appropriate).
> I intend to address that missing propagation of exceptions in a
> subsequent patch series; until it's addressed, the code setting
> exceptions won't actually do anything useful.  (There is also code in
> the x87 emulation, including that of fscale, that would result in
> spurious exceptions being set from a naive propagation of exceptions
> from the softfloat state, and thus will need updating to avoid
> propagating inappropriate exceptions when such propagation is
> implemented.)
> 
> Joseph Myers (5):
>    target/i386: implement special cases for fxtract
>    target/i386: fix fscale handling of signaling NaN
>    target/i386: fix fscale handling of invalid exponent encodings
>    target/i386: fix fscale handling of infinite exponents
>    target/i386: fix fscale handling of rounding precision
> 
>   target/i386/fpu_helper.c           |  59 +++++++++++++-
>   tests/tcg/i386/test-i386-fscale.c  | 108 ++++++++++++++++++++++++++
>   tests/tcg/i386/test-i386-fxtract.c | 120 +++++++++++++++++++++++++++++
>   3 files changed, 285 insertions(+), 2 deletions(-)
>   create mode 100644 tests/tcg/i386/test-i386-fscale.c
>   create mode 100644 tests/tcg/i386/test-i386-fxtract.c
>