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>

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)) {
+        error = POWERPC_EXCP_FP_ZX;
+    } else if (fpscr & FP_VE) {
+        if (fpscr & FP_VXSOFT) {
+            error = POWERPC_EXCP_FP_VXSOFT;
+        } else if (fpscr & FP_VXSNAN) {
+            error = POWERPC_EXCP_FP_VXSNAN;
+        } else if (fpscr & FP_VXISI) {
+            error = POWERPC_EXCP_FP_VXISI;
+        } else if (fpscr & FP_VXIDI) {
+            error = POWERPC_EXCP_FP_VXIDI;
+        } else if (fpscr & FP_VXZDZ) {
+            error = POWERPC_EXCP_FP_VXZDZ;
+        } else if (fpscr & FP_VXIMZ) {
+            error = POWERPC_EXCP_FP_VXIMZ;
+        } else if (fpscr & FP_VXVC) {
+            error = POWERPC_EXCP_FP_VXVC;
+        } else if (fpscr & FP_VXSQRT) {
+            error = POWERPC_EXCP_FP_VXSQRT;
+        } else if (fpscr & FP_VXCVI) {
+            error = POWERPC_EXCP_FP_VXCVI;
+        } else {
+            return;
+        }
+    } else {
+        return;
+    }
+    cs->exception_index = POWERPC_EXCP_PROGRAM;
+    env->error_code = error | POWERPC_EXCP_FP;
+    /* Deferred floating-point exception after target FPSCR update */
+    if (fp_exceptions_enabled(env)) {
+        raise_exception_err_ra(env, cs->exception_index,
+                               env->error_code, GETPC());
+    }
+}
+
 static void do_float_check_status(CPUPPCState *env, uintptr_t raddr)
 {
     CPUState *cs = env_cpu(env);

target/ppc/helper.h

@@ -63,6 +63,7 @@ DEF_HELPER_FLAGS_1(cntlzw32, TCG_CALL_NO_RWG_SE, i32, i32)
 DEF_HELPER_FLAGS_2(brinc, TCG_CALL_NO_RWG_SE, tl, tl, tl)
 
 DEF_HELPER_1(float_check_status, void, env)
+DEF_HELPER_1(fpscr_check_status, void, env)
 DEF_HELPER_1(reset_fpstatus, void, env)
 DEF_HELPER_2(compute_fprf_float64, void, env, i64)
 DEF_HELPER_3(store_fpscr, void, env, i64, i32)

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)