Re: [PATCH v3 1/3] target/ppc: Fixed call to deferred exception

[Richard Henderson <richard.henderson@linaro.org>]

On 11/24/21 6:25 PM, Lucas Mateus Castro (alqotel) wrote:
> mtfsf, mtfsfi and mtfsb1 instructions call helper_float_check_status
> after updating the value of FPSCR, but helper_float_check_status
> checks fp_status and fp_status isn't updated based on FPSCR and
> since the value of fp_status is reset earlier in the instruction,
> it's always 0.
> 
> Because of this helper_float_check_status would change the FI bit to 0
> as this bit checks if the last operation was inexact and
> float_flag_inexact is always 0.
> 
> These instructions also don't throw exceptions correctly since
> helper_float_check_status throw exceptions based on fp_status.
> 
> This commit created a new helper, helper_fpscr_check_status that checks
> FPSCR value instead of fp_status and checks for a larger variety of
> exceptions than do_float_check_status.
> 
> Since fp_status isn't used, gen_reset_fpstatus() was removed.
> 
> The hardware used to compare QEMU's behavior to was a Power9.
> 
> Signed-off-by: Lucas Mateus Castro (alqotel) <lucas.araujo@eldorado.org.br>
> ---
>   target/ppc/fpu_helper.c            | 48 ++++++++++++++++++++++++++++++
>   target/ppc/helper.h                |  1 +
>   target/ppc/translate/fp-impl.c.inc |  9 ++----
>   3 files changed, 52 insertions(+), 6 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~