target/ppc: Fixed call to deferred exception

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.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Lucas Mateus Castro (alqotel) <lucas.araujo@eldorado.org.br>
Message-Id: <20211201163808.440385-2-lucas.araujo@eldorado.org.br>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

1 files changed, 3 insertions, 6 deletions

diff --git a/target/ppc/translate/fp-impl.c.inc b/target/ppc/translate/fp-impl.c.inc
index c9e05201d9..8afd6a087d 100644
--- a/target/ppc/translate/fp-impl.c.inc
+++ b/target/ppc/translate/fp-impl.c.inc
@@ -769,7 +769,6 @@ static void gen_mtfsb1(DisasContext *ctx)
         return;
     }
     crb = 31 - crbD(ctx->opcode);
-    gen_reset_fpstatus();
     /* XXX: we pretend we can only do IEEE floating-point computations */
     if (likely(crb != FPSCR_FEX && crb != FPSCR_VX && crb != FPSCR_NI)) {
         TCGv_i32 t0;
@@ -782,7 +781,7 @@ static void gen_mtfsb1(DisasContext *ctx)
         tcg_gen_shri_i32(cpu_crf[1], cpu_crf[1], FPSCR_OX);
     }
     /* We can raise a deferred exception */
-    gen_helper_float_check_status(cpu_env);
+    gen_helper_fpscr_check_status(cpu_env);
 }
 
 /* mtfsf */
@@ -803,7 +802,6 @@ static void gen_mtfsf(DisasContext *ctx)
         gen_inval_exception(ctx, POWERPC_EXCP_INVAL_INVAL);
         return;
     }
-    gen_reset_fpstatus();
     if (l) {
         t0 = tcg_const_i32((ctx->insns_flags2 & PPC2_ISA205) ? 0xffff : 0xff);
     } else {
@@ -818,7 +816,7 @@ static void gen_mtfsf(DisasContext *ctx)
         tcg_gen_shri_i32(cpu_crf[1], cpu_crf[1], FPSCR_OX);
     }
     /* We can raise a deferred exception */
-    gen_helper_float_check_status(cpu_env);
+    gen_helper_fpscr_check_status(cpu_env);
     tcg_temp_free_i64(t1);
 }
 
@@ -840,7 +838,6 @@ static void gen_mtfsfi(DisasContext *ctx)
         return;
     }
     sh = (8 * w) + 7 - bf;
-    gen_reset_fpstatus();
     t0 = tcg_const_i64(((uint64_t)FPIMM(ctx->opcode)) << (4 * sh));
     t1 = tcg_const_i32(1 << sh);
     gen_helper_store_fpscr(cpu_env, t0, t1);
@@ -851,7 +848,7 @@ static void gen_mtfsfi(DisasContext *ctx)
         tcg_gen_shri_i32(cpu_crf[1], cpu_crf[1], FPSCR_OX);
     }
     /* We can raise a deferred exception */
-    gen_helper_float_check_status(cpu_env);
+    gen_helper_fpscr_check_status(cpu_env);
 }
 
 static void gen_qemu_ld32fs(DisasContext *ctx, TCGv_i64 dest, TCGv addr)