Do not use const attribute for nan functions (bug 23277) [committed]
Commit Message
As in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86113 for
__builtin_nan, bits/mathcalls.h wrongly declares the nan function with
the __const__ attribute. Because the function reads memory pointed to
by an argument, it's only pure, not const. This patch removes the
incorrect attribute and adds a testcase for the bug. No __pure__
attribute is added to replace the incorrect __const__ one, since that
would introduce problems when using GCC versions that have the
incorrect built-in __const__ attribute and warn for the combination of
those two attributes.
Tested for x86_64. Committed.
2018-06-12 Joseph Myers <joseph@codesourcery.com>
[BZ #23277]
* math/bits/mathcalls.h [__USE_ISOC99] (nan): Do not use __const__
attribute.
* math/test-nan-const.c: New file.
* math/Makefile (tests): Add test-nan-const.
(CFLAGS-test-nan-const.c): New variable.
Comments
* Joseph Myers:
> +static int
> +do_test (void)
> +{
> + char buf[2] = { '2', 0 };
> + float a = nanf (buf);
> + buf[0] = '3';
> + float b = nanf (buf);
> + return memcmp (&a, &b, sizeof (float)) == 0;
> +}
By the way, there's TEST_COMPARE_BLOB now, which can simplify
debugging of test failures because the failure message includes the
blobs that differ.
On Tue, 12 Jun 2018, Florian Weimer wrote:
> * Joseph Myers:
>
> > +static int
> > +do_test (void)
> > +{
> > + char buf[2] = { '2', 0 };
> > + float a = nanf (buf);
> > + buf[0] = '3';
> > + float b = nanf (buf);
> > + return memcmp (&a, &b, sizeof (float)) == 0;
> > +}
>
> By the way, there's TEST_COMPARE_BLOB now, which can simplify
> debugging of test failures because the failure message includes the
> blobs that differ.
In this case, the requirement is actually that the blobs must differ, with
a failure if they are the same (if the compiler optimized out the second
nanf call and so produced the same NaN for both calls).
* Joseph Myers:
> On Tue, 12 Jun 2018, Florian Weimer wrote:
>
>> * Joseph Myers:
>>
>> > +static int
>> > +do_test (void)
>> > +{
>> > + char buf[2] = { '2', 0 };
>> > + float a = nanf (buf);
>> > + buf[0] = '3';
>> > + float b = nanf (buf);
>> > + return memcmp (&a, &b, sizeof (float)) == 0;
>> > +}
>>
>> By the way, there's TEST_COMPARE_BLOB now, which can simplify
>> debugging of test failures because the failure message includes the
>> blobs that differ.
>
> In this case, the requirement is actually that the blobs must differ, with
> a failure if they are the same (if the compiler optimized out the second
> nanf call and so produced the same NaN for both calls).
Oh, right. I was confused.
@@ -235,7 +235,7 @@ tests = test-matherr-3 test-fenv basic-test \
test-iseqsig-excess-precision test-flt-eval-method \
test-fp-ilogb-constants test-fp-llogb-constants \
test-fe-snans-always-signal test-finite-macros test-narrow-macros \
- $(tests-static)
+ test-nan-const $(tests-static)
tests-static = test-fpucw-static test-fpucw-ieee-static \
test-signgam-uchar-static test-signgam-uchar-init-static \
test-signgam-uint-static test-signgam-uint-init-static \
@@ -442,6 +442,8 @@ CFLAGS-test-fe-snans-always-signal.c += -fsignaling-nans
CFLAGS-test-finite-macros.c += -ffinite-math-only
+CFLAGS-test-nan-const.c += -fno-builtin
+
include ../Rules
gen-all-calls = $(gen-libm-calls) $(gen-calls)
@@ -198,7 +198,7 @@ __MATHCALLX (copysign,, (_Mdouble_ __x, _Mdouble_ __y), (__const__));
#ifdef __USE_ISOC99
/* Return representation of qNaN for double type. */
-__MATHCALLX (nan,, (const char *__tagb), (__const__));
+__MATHCALL (nan,, (const char *__tagb));
#endif
new file mode 100644
@@ -0,0 +1,32 @@
+/* Test nan functions do not have const attribute. Bug 23277.
+ Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <math.h>
+#include <string.h>
+
+static int
+do_test (void)
+{
+ char buf[2] = { '2', 0 };
+ float a = nanf (buf);
+ buf[0] = '3';
+ float b = nanf (buf);
+ return memcmp (&a, &b, sizeof (float)) == 0;
+}
+
+#include <support/test-driver.c>