[PATCH] Fix up undefined signed overflows in FIXED_SSNEG (PR libgcc/55451)
Jakub Jelinek
jakub@redhat.com
Tue Dec 11 15:08:00 GMT 2012
On Tue, Dec 11, 2012 at 06:52:38AM -0800, Ian Lance Taylor wrote:
> I presume that the intent of the obfuscation is to make SSNEG look
> exactly like SSSUB. And SSSUB appears to have the exact problems that
> you are fixing here. So I think you ought to fix both the same way.
Ugh, I was hoping for a small patch.
Here is updated patch for the 5 routines I could quickly find by looking
around.
2012-12-11 Jakub Jelinek <jakub@redhat.com>
PR libgcc/55451
* fixed-bit.c (FIXED_SSADD, FIXED_USADD, FIXED_SSSUB, FIXED_USSUB,
FIXED_SSNEG): Avoid undefined signed overflows.
--- libgcc/fixed-bit.c.jj 2011-11-04 07:49:37.000000000 +0100
+++ libgcc/fixed-bit.c 2012-12-11 16:01:30.178653065 +0100
@@ -1,5 +1,5 @@
/* This is a software fixed-point library.
- Copyright (C) 2007, 2009, 2011 Free Software Foundation, Inc.
+ Copyright (C) 2007, 2009, 2011, 2012 Free Software Foundation, Inc.
This file is part of GCC.
@@ -80,15 +80,14 @@ FIXED_SSADD (FIXED_C_TYPE a, FIXED_C_TYP
INT_C_TYPE x, y, z;
memcpy (&x, &a, FIXED_SIZE);
memcpy (&y, &b, FIXED_SIZE);
- z = x + y;
+ z = x + (UINT_C_TYPE) y;
if ((((x ^ y) >> I_F_BITS) & 1) == 0)
{
if (((z ^ x) >> I_F_BITS) & 1)
{
- z = 1;
- z = z << I_F_BITS;
- if (x >= 0)
- z--;
+ z = ((UINT_C_TYPE) 1) << I_F_BITS;
+ if (x >= 0)
+ z -= (UINT_C_TYPE) 1;
}
}
#if HAVE_PADDING_BITS
@@ -108,7 +107,7 @@ FIXED_USADD (FIXED_C_TYPE a, FIXED_C_TYP
INT_C_TYPE x, y, z;
memcpy (&x, &a, FIXED_SIZE);
memcpy (&y, &b, FIXED_SIZE);
- z = x + y;
+ z = x + (UINT_C_TYPE) y;
#if HAVE_PADDING_BITS
z = z << PADDING_BITS;
z = z >> PADDING_BITS;
@@ -152,15 +151,14 @@ FIXED_SSSUB (FIXED_C_TYPE a, FIXED_C_TYP
INT_C_TYPE x, y, z;
memcpy (&x, &a, FIXED_SIZE);
memcpy (&y, &b, FIXED_SIZE);
- z = x - y;
+ z = x - (UINT_C_TYPE) y;
if (((x ^ y) >> I_F_BITS) & 1)
{
if (((z ^ x) >> I_F_BITS) & 1)
{
- z = 1;
- z = z << I_F_BITS;
- if (x >= 0)
- z--;
+ z = ((UINT_C_TYPE) 1) << I_F_BITS;
+ if (x >= 0)
+ z -= (UINT_C_TYPE) 1;
}
}
#if HAVE_PADDING_BITS
@@ -180,7 +178,7 @@ FIXED_USSUB (FIXED_C_TYPE a, FIXED_C_TYP
INT_C_TYPE x, y, z;
memcpy (&x, &a, FIXED_SIZE);
memcpy (&y, &b, FIXED_SIZE);
- z = x - y;
+ z = x - (UINT_C_TYPE) y;
if (x < y)
z = 0;
#if HAVE_PADDING_BITS
@@ -569,16 +567,11 @@ FIXED_SSNEG (FIXED_C_TYPE a)
INT_C_TYPE x, y, z;
memcpy (&y, &a, FIXED_SIZE);
x = 0;
- z = x - y;
+ z = x - (UINT_C_TYPE) y;
if (((x ^ y) >> I_F_BITS) & 1)
{
if (((z ^ x) >> I_F_BITS) & 1)
- {
- z = 1;
- z = z << I_F_BITS;
- if (x >= 0)
- z--;
- }
+ z = (((UINT_C_TYPE) 1) << I_F_BITS) - 1;
}
#if HAVE_PADDING_BITS
z = z << PADDING_BITS;
Jakub
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