[Qemu-devel] [PATCH v2 14/17] target-alpha: Raise EXC_M_INV properly for fp inputs

[Richard Henderson <rth@twiddle.net>]

Ignore DNZ if software completion isn't used.  Raise INV for
denormals in system mode so the OS completion handler sees them.

Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 target-alpha/fpu_helper.c | 32 ++++++++++++++++++++++----------
 target-alpha/helper.h     |  1 +
 target-alpha/translate.c  |  7 +++++++
 3 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/target-alpha/fpu_helper.c b/target-alpha/fpu_helper.c
index db523fb..ea1f2e2 100644
--- a/target-alpha/fpu_helper.c
+++ b/target-alpha/fpu_helper.c
@@ -104,16 +104,14 @@ void helper_ieee_input(CPUAlphaState *env, uint64_t val)
     uint64_t frac = val & 0xfffffffffffffull;
 
     if (exp == 0) {
-        /* Denormals without DNZ set raise an exception.  */
-        if (frac != 0 && !env->fp_status.flush_inputs_to_zero) {
-            arith_excp(env, GETPC(), EXC_M_UNF, 0);
+        /* Denormals without /S raise an exception.  */
+        if (frac != 0) {
+            arith_excp(env, GETPC(), EXC_M_INV, 0);
         }
     } else if (exp == 0x7ff) {
         /* Infinity or NaN.  */
-        /* ??? I'm not sure these exception bit flags are correct.  I do
-           know that the Linux kernel, at least, doesn't rely on them and
-           just emulates the insn to figure out what exception to use.  */
-        arith_excp(env, GETPC(), frac ? EXC_M_INV : EXC_M_FOV, 0);
+        env->fpcr |= FPCR_INV;
+        arith_excp(env, GETPC(), EXC_M_INV, 0);
     }
 }
 
@@ -124,16 +122,30 @@ void helper_ieee_input_cmp(CPUAlphaState *env, uint64_t val)
     uint64_t frac = val & 0xfffffffffffffull;
 
     if (exp == 0) {
-        /* Denormals without DNZ set raise an exception.  */
-        if (frac != 0 && !env->fp_status.flush_inputs_to_zero) {
-            arith_excp(env, GETPC(), EXC_M_UNF, 0);
+        /* Denormals without /S raise an exception.  */
+        if (frac != 0) {
+            arith_excp(env, GETPC(), EXC_M_INV, 0);
         }
     } else if (exp == 0x7ff && frac) {
         /* NaN.  */
+        env->fpcr |= FPCR_INV;
         arith_excp(env, GETPC(), EXC_M_INV, 0);
     }
 }
 
+/* Input handing with software completion.  Trap for denorms, unless DNZ
+   is set.  If we try to support DNOD (which none of the produced hardware
+   did, AFAICS), we'll need to suppress the trap when FPCR.DNOD is set;
+   then the code downstream of that will need to cope with denorms sans
+   flush_input_to_zero.  Most of it should work sanely, but there's
+   nothing to compare with.  */
+void helper_ieee_input_s(CPUAlphaState *env, uint64_t val)
+{
+    if (unlikely(2 * val - 1 < 0x1fffffffffffffull)
+        && !env->fp_status.flush_inputs_to_zero) {
+        arith_excp(env, GETPC(), EXC_M_INV | EXC_M_SWC, 0);
+    }
+}
 
 /* S floating (single) */
 
diff --git a/target-alpha/helper.h b/target-alpha/helper.h
index 5b1a5d9..780b0dc 100644
--- a/target-alpha/helper.h
+++ b/target-alpha/helper.h
@@ -86,6 +86,7 @@ DEF_HELPER_FLAGS_3(fp_exc_raise_s, TCG_CALL_NO_WG, void, env, i32, i32)
 
 DEF_HELPER_FLAGS_2(ieee_input, TCG_CALL_NO_WG, void, env, i64)
 DEF_HELPER_FLAGS_2(ieee_input_cmp, TCG_CALL_NO_WG, void, env, i64)
+DEF_HELPER_FLAGS_2(ieee_input_s, TCG_CALL_NO_WG, void, env, i64)
 DEF_HELPER_FLAGS_2(cvtql_v_input, TCG_CALL_NO_WG, void, env, i64)
 
 #if !defined (CONFIG_USER_ONLY)
diff --git a/target-alpha/translate.c b/target-alpha/translate.c
index f0556b0..4c441a9 100644
--- a/target-alpha/translate.c
+++ b/target-alpha/translate.c
@@ -658,6 +658,13 @@ static TCGv gen_ieee_input(DisasContext *ctx, int reg, int fn11, int is_cmp)
             } else {
                 gen_helper_ieee_input(cpu_env, val);
             }
+        } else {
+#ifndef CONFIG_USER_ONLY
+            /* In system mode, raise exceptions for denormals like real
+               hardware.  In user mode, proceed as if the OS completion
+               handler is handling the denormal as per spec.  */
+            gen_helper_ieee_input_s(cpu_env, val);
+#endif
         }
     }
     return val;
-- 
2.1.0