On Wed, 24 Nov 2021, 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(-)
diff --git a/target/ppc/fpu_helper.c b/target/ppc/fpu_helper.c
index c4896cecc8..bb72715827 100644
--- a/target/ppc/fpu_helper.c
+++ b/target/ppc/fpu_helper.c
@@ -414,6 +414,54 @@ void helper_store_fpscr(CPUPPCState *env, uint64_t val,
uint32_t nibbles)
ppc_store_fpscr(env, val);
}
+void helper_fpscr_check_status(CPUPPCState *env)
+{
+ CPUState *cs = env_cpu(env);
+ target_ulong fpscr = env->fpscr;
+ int error = 0;
+
+ if ((fpscr & FP_OX) && (fpscr & FP_OE)) {
+ error = POWERPC_EXCP_FP_OX;
+ } else if ((fpscr & FP_UX) && (fpscr & FP_UE)) {
+ error = POWERPC_EXCP_FP_UX;
+ } else if ((fpscr & FP_XX) && (fpscr & FP_XE)) {
+ error = POWERPC_EXCP_FP_XX;
+ } else if ((fpscr & FP_ZX) && (fpscr & FP_ZE)) {
I wonder if these tests could be simplified by combining the masks if you
want to test for both bits set so e.g. fpscr & (FP_ZX | FP_ZE) should be the
same, shouldn't it?