From 3e934b99c81800f8699f4c958a2559e4a774b473 Mon Sep 17 00:00:00 2001
From: Richard Henderson <richard.henderson@linaro.org>
Date: Thu, 30 Apr 2020 07:22:48 -0400
Subject: [PATCH] softfloat: Fix BAD_SHIFT from normalizeFloatx80Subnormal

All other calls to normalize*Subnormal detect zero input before
the call -- this is the only outlier. This case can happen with
+0.0 + +0.0 = +0.0 or -0.0 + -0.0 = -0.0, so return a zero of
the correct sign.

Reported-by: Coverity (CID 1421991)

Backports commit 2f311075b7a74124098effc72290767b02869561 from qemu
---
 qemu/fpu/softfloat.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/qemu/fpu/softfloat.c b/qemu/fpu/softfloat.c
index 241da0b1..13a01713 100644
--- a/qemu/fpu/softfloat.c
+++ b/qemu/fpu/softfloat.c
@@ -5818,6 +5818,9 @@ static floatx80 addFloatx80Sigs(floatx80 a, floatx80 b, flag zSign,
         zSig1 = 0;
         zSig0 = aSig + bSig;
         if ( aExp == 0 ) {
+            if (zSig0 == 0) {
+                return packFloatx80(zSign, 0, 0);
+            }
             normalizeFloatx80Subnormal( zSig0, &zExp, &zSig0 );
             goto roundAndPack;
         }