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i686: Do not raise exception traps on fesetexcept (BZ 30989)
According to ISO C23 (7.6.4.4), fesetexcept is supposed to set floating-point exception flags without raising a trap (unlike feraiseexcept, which is supposed to raise a trap if feenableexcept was called with the appropriate argument). The flags can be set in the 387 unit or in the SSE unit. To set a flag, it is sufficient to do it in the SSE unit, because that is guaranteed to not trap. However, on i386 CPUs that have only a 387 unit, set the flags in the 387, as long as this cannot trap. Checked on i686-linux-gnu. Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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@ -19,6 +19,7 @@
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#include <fenv.h>
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#include <stdio.h>
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#include <math-tests.h>
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#include <math-barriers.h>
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static int
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do_test (void)
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@ -41,12 +42,32 @@ do_test (void)
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/* Verify fesetexcept does not cause exception traps. For architectures
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where setting the exception might result in traps the function should
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return a nonzero value. */
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return a nonzero value.
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Also check if the function does not alter the exception mask. */
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ret = fesetexcept (FE_ALL_EXCEPT);
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_Static_assert (!(EXCEPTION_SET_FORCES_TRAP && !EXCEPTION_TESTS(float)),
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"EXCEPTION_SET_FORCES_TRAP only makes sense if the "
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"architecture suports exceptions");
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{
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int exc_before = fegetexcept ();
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ret = fesetexcept (FE_ALL_EXCEPT);
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int exc_after = fegetexcept ();
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if (exc_before != exc_after)
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{
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puts ("fesetexcept (FE_ALL_EXCEPT) changed the exceptions mask");
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return 1;
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}
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}
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/* Execute some floating-point operations, since on some CPUs exceptions
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triggers a trap only at the next floating-point instruction. */
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volatile double a = 1.0;
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volatile double b = a + a;
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math_force_eval (b);
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volatile long double al = 1.0L;
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volatile long double bl = al + al;
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math_force_eval (bl);
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if (ret == 0)
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{
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@ -72,5 +93,4 @@ do_test (void)
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return result;
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}
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#define TEST_FUNCTION do_test ()
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#include "../test-skeleton.c"
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#include <support/test-driver.c>
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@ -17,15 +17,53 @@
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<https://www.gnu.org/licenses/>. */
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#include <fenv.h>
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#include <ldsodefs.h>
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int
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fesetexcept (int excepts)
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{
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fenv_t temp;
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/* The flags can be set in the 387 unit or in the SSE unit. To set a flag,
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it is sufficient to do it in the SSE unit, because that is guaranteed to
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not trap. However, on i386 CPUs that have only a 387 unit, set the flags
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in the 387, as long as this cannot trap. */
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__asm__ ("fnstenv %0" : "=m" (*&temp));
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temp.__status_word |= excepts & FE_ALL_EXCEPT;
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__asm__ ("fldenv %0" : : "m" (*&temp));
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excepts &= FE_ALL_EXCEPT;
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if (CPU_FEATURE_USABLE (SSE))
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{
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/* Get the control word of the SSE unit. */
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unsigned int mxcsr;
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__asm__ ("stmxcsr %0" : "=m" (*&mxcsr));
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/* Set relevant flags. */
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mxcsr |= excepts;
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/* Put the new data in effect. */
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__asm__ ("ldmxcsr %0" : : "m" (*&mxcsr));
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}
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else
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{
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fenv_t temp;
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/* Note: fnstenv masks all floating-point exceptions until the fldenv
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or fldcw below. */
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__asm__ ("fnstenv %0" : "=m" (*&temp));
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/* Set relevant flags. */
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temp.__status_word |= excepts;
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if ((~temp.__control_word) & excepts)
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{
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/* Setting the exception flags may trigger a trap (at the next
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floating-point instruction, but that does not matter).
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ISO C23 (7.6.4.4) does not allow it. */
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__asm__ volatile ("fldcw %0" : : "m" (*&temp.__control_word));
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return -1;
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}
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/* Store the new status word (along with the rest of the environment). */
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__asm__ ("fldenv %0" : : "m" (*&temp));
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}
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return 0;
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}
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29
sysdeps/i386/fpu/math-tests-trap-force.h
Normal file
29
sysdeps/i386/fpu/math-tests-trap-force.h
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@ -0,0 +1,29 @@
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/* Configuration for math tests: support for setting exception flags
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without causing enabled traps. i686 version.
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Copyright (C) 2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#ifndef I386_FPU_MATH_TESTS_TRAP_FORCE_H
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#define I386_FPU_MATH_TESTS_TRAP_FORCE_H 1
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#include <cpu-features.h>
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/* Setting exception flags in FPU Status Register results in enabled traps for
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those exceptions being taken. */
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#define EXCEPTION_SET_FORCES_TRAP !CPU_FEATURE_USABLE (SSE)
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#endif /* math-tests-trap-force.h. */
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@ -22,17 +22,8 @@
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#include <stdbool.h>
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#include <stdint.h>
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#include <stdio.h>
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static bool
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have_sse2 (void)
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{
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unsigned int eax, ebx, ecx, edx;
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if (!__get_cpuid (1, &eax, &ebx, &ecx, &edx))
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return false;
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return (edx & bit_SSE2) != 0;
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}
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#include <cpu-features.h>
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#include <support/check.h>
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static uint32_t
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get_sse_mxcsr (void)
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@ -164,13 +155,9 @@ sse_tests (void)
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static int
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do_test (void)
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{
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if (!have_sse2 ())
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{
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puts ("CPU does not support SSE2, cannot test");
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return 0;
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}
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if (!CPU_FEATURE_USABLE (SSE2))
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FAIL_UNSUPPORTED ("CPU does not support SSE2");
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return sse_tests ();
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}
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#define TEST_FUNCTION do_test ()
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#include <test-skeleton.c>
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#include <support/test-driver.c>
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