target-arm: Add support for 'Standard FPSCR Value' as used by Neon

Add support to the ARM helper routines for a second fp_status value
which should be used for operations which the ARM ARM indicates use
"ARM standard floating-point arithmetic" rather than being controlled
by the rounding/flush/NaN settings in the FPSCR.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 13 insertions, 0 deletions

diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 340933ef50..e501cf59f1 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -173,7 +173,20 @@ typedef struct CPUARMState {
         /* scratch space when Tn are not sufficient.  */
         uint32_t scratch[8];
 
+        /* fp_status is the "normal" fp status. standard_fp_status retains
+         * values corresponding to the ARM "Standard FPSCR Value", ie
+         * default-NaN, flush-to-zero, round-to-nearest and is used by
+         * any operations (generally Neon) which the architecture defines
+         * as controlled by the standard FPSCR value rather than the FPSCR.
+         *
+         * To avoid having to transfer exception bits around, we simply
+         * say that the FPSCR cumulative exception flags are the logical
+         * OR of the flags in the two fp statuses. This relies on the
+         * only thing which needs to read the exception flags being
+         * an explicit FPSCR read.
+         */
         float_status fp_status;
+        float_status standard_fp_status;
     } vfp;
     uint32_t exclusive_addr;
     uint32_t exclusive_val;