softfloat: Fix BAD_SHIFT from normalizeFloatx80Subnormal

[PATCH] softfloat: Fix BAD_SHIFT from normalizeFloatx80Subnormal

Richard Henderson posted 1 patch 4 years ago

Download mbox

Test docker-mingw@fedora passed

Test docker-quick@centos7 passed

Test FreeBSD passed

Test checkpatch passed

Test asan passed

Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20200327232042.10008-1-richard.henderson@linaro.org

Maintainers: Aurelien Jarno <aurelien@aurel32.net>, Peter Maydell <peter.maydell@linaro.org>, "Alex Bennée" <alex.bennee@linaro.org>

fpu/softfloat.c | 3 +++
1 file changed, 3 insertions(+)

Expand all Fold all

[PATCH] softfloat: Fix BAD_SHIFT from normalizeFloatx80Subnormal

Posted by Richard Henderson 4 years ago

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)
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 fpu/softfloat.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 301ce3b537..ae6ba71854 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -5856,6 +5856,9 @@ 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;
         }
-- 
2.20.1

Re: [PATCH] softfloat: Fix BAD_SHIFT from normalizeFloatx80Subnormal

Posted by Alex Bennée 4 years ago

Richard Henderson <richard.henderson@linaro.org> writes:

> 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)
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Queued to for-5.0/random-fixes, thanks.

> ---
>  fpu/softfloat.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index 301ce3b537..ae6ba71854 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -5856,6 +5856,9 @@ 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;
>          }


-- 
Alex Bennée