| Message ID | 20231106132713.953501-3-adhemerval.zanella@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | Multiple floating-point environment fixes | expand |
On 11/6/23 08:27, Adhemerval Zanella wrote: > 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. LGTM. Reviewed-by: Carlos O'Donell <carlos@redhat.com> > --- > math/test-fesetexcept-traps.c | 28 ++++++++++++--- > sysdeps/i386/fpu/fesetexcept.c | 46 +++++++++++++++++++++--- > sysdeps/i386/fpu/math-tests-trap-force.h | 29 +++++++++++++++ > sysdeps/x86/fpu/test-fenv-sse-2.c | 23 +++--------- > 4 files changed, 100 insertions(+), 26 deletions(-) > create mode 100644 sysdeps/i386/fpu/math-tests-trap-force.h > > diff --git a/math/test-fesetexcept-traps.c b/math/test-fesetexcept-traps.c > index 96f6c4752f..8a5c0bca80 100644 > --- a/math/test-fesetexcept-traps.c > +++ b/math/test-fesetexcept-traps.c > @@ -19,6 +19,7 @@ > #include <fenv.h> > #include <stdio.h> > #include <math-tests.h> > +#include <math-barriers.h> > > static int > do_test (void) > @@ -41,8 +42,28 @@ do_test (void) > > /* Verify fesetexcept does not cause exception traps. For architectures > where setting the exception might result in traps the function should > - return a nonzero value. */ > - ret = fesetexcept (FE_ALL_EXCEPT); > + return a nonzero value. > + Also check if the function does not alter the exception mask. */ > + { > + int exc_before = fegetexcept (); > + ret = fesetexcept (FE_ALL_EXCEPT); > + int exc_after = fegetexcept (); > + if (exc_before != exc_after) > + { > + puts ("fesetexcept (FE_ALL_EXCEPT) changed the exceptions mask"); > + return 1; > + } > + } > + > + /* Execute some floating-point operations, since on some CPUs exceptions > + triggers a trap only at the next floating-point instruction. */ Correct, this is called delayed floating point exception handling and hppa has this too. > + volatile double a = 1.0; > + volatile double b = a + a; > + math_force_eval (b); > + volatile long double al = 1.0L; > + volatile long double bl = al + al; > + math_force_eval (bl); > + > if (ret == 0) > puts ("fesetexcept (FE_ALL_EXCEPT) succeeded"); > else if (!EXCEPTION_SET_FORCES_TRAP) > @@ -61,5 +82,4 @@ do_test (void) > return result; > } > > -#define TEST_FUNCTION do_test () > -#include "../test-skeleton.c" > +#include <support/test-driver.c> > diff --git a/sysdeps/i386/fpu/fesetexcept.c b/sysdeps/i386/fpu/fesetexcept.c > index 18949e982a..58f577d93d 100644 > --- a/sysdeps/i386/fpu/fesetexcept.c > +++ b/sysdeps/i386/fpu/fesetexcept.c > @@ -17,15 +17,53 @@ > <https://www.gnu.org/licenses/>. */ > > #include <fenv.h> > +#include <ldsodefs.h> > > int > fesetexcept (int excepts) > { > - fenv_t temp; > + /* 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. */ > > - __asm__ ("fnstenv %0" : "=m" (*&temp)); > - temp.__status_word |= excepts & FE_ALL_EXCEPT; > - __asm__ ("fldenv %0" : : "m" (*&temp)); > + excepts &= FE_ALL_EXCEPT; > + > + if (CPU_FEATURE_USABLE (SSE)) > + { > + /* Get the control word of the SSE unit. */ > + unsigned int mxcsr; > + __asm__ ("stmxcsr %0" : "=m" (*&mxcsr)); > + > + /* Set relevant flags. */ > + mxcsr |= excepts; > + > + /* Put the new data in effect. */ > + __asm__ ("ldmxcsr %0" : : "m" (*&mxcsr)); > + } > + else > + { > + fenv_t temp; > + > + /* Note: fnstenv masks all floating-point exceptions until the fldenv > + or fldcw below. */ > + __asm__ ("fnstenv %0" : "=m" (*&temp)); > + > + /* Set relevant flags. */ > + temp.__status_word |= excepts; > + > + if ((~temp.__control_word) & excepts) > + { > + /* Setting the exception flags may trigger a trap (at the next > + floating-point instruction, but that does not matter). > + ISO C23 (7.6.4.4) does not allow it. */ > + __asm__ volatile ("fldcw %0" : : "m" (*&temp.__control_word)); > + return -1; > + } > + > + /* Store the new status word (along with the rest of the environment). */ > + __asm__ ("fldenv %0" : : "m" (*&temp)); > + } > > return 0; > } > diff --git a/sysdeps/i386/fpu/math-tests-trap-force.h b/sysdeps/i386/fpu/math-tests-trap-force.h > new file mode 100644 > index 0000000000..f41e1ffc2d > --- /dev/null > +++ b/sysdeps/i386/fpu/math-tests-trap-force.h > @@ -0,0 +1,29 @@ > +/* Configuration for math tests: support for setting exception flags > + without causing enabled traps. i686 version. > + Copyright (C) 2023 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 > + <https://www.gnu.org/licenses/>. */ > + > +#ifndef I386_FPU_MATH_TESTS_TRAP_FORCE_H > +#define I386_FPU_MATH_TESTS_TRAP_FORCE_H 1 > + > +#include <cpu-features.h> > + > +/* Setting exception flags in FPU Status Register results in enabled traps for > + those exceptions being taken. */ > +#define EXCEPTION_SET_FORCES_TRAP !CPU_FEATURE_USABLE (SSE) > + > +#endif /* math-tests-trap-force.h. */ > diff --git a/sysdeps/x86/fpu/test-fenv-sse-2.c b/sysdeps/x86/fpu/test-fenv-sse-2.c > index f3e820b6ed..7a0503790f 100644 > --- a/sysdeps/x86/fpu/test-fenv-sse-2.c > +++ b/sysdeps/x86/fpu/test-fenv-sse-2.c > @@ -22,17 +22,8 @@ > #include <stdbool.h> > #include <stdint.h> > #include <stdio.h> > - > -static bool > -have_sse2 (void) > -{ > - unsigned int eax, ebx, ecx, edx; > - > - if (!__get_cpuid (1, &eax, &ebx, &ecx, &edx)) > - return false; > - > - return (edx & bit_SSE2) != 0; > -} > +#include <cpu-features.h> > +#include <support/check.h> > > static uint32_t > get_sse_mxcsr (void) > @@ -164,13 +155,9 @@ sse_tests (void) > static int > do_test (void) > { > - if (!have_sse2 ()) > - { > - puts ("CPU does not support SSE2, cannot test"); > - return 0; > - } > + if (!CPU_FEATURE_USABLE (SSE2)) > + FAIL_UNSUPPORTED ("CPU does not support SSE2"); > return sse_tests (); > } > > -#define TEST_FUNCTION do_test () > -#include <test-skeleton.c> > +#include <support/test-driver.c>
diff --git a/math/test-fesetexcept-traps.c b/math/test-fesetexcept-traps.c index 96f6c4752f..8a5c0bca80 100644 --- a/math/test-fesetexcept-traps.c +++ b/math/test-fesetexcept-traps.c @@ -19,6 +19,7 @@ #include <fenv.h> #include <stdio.h> #include <math-tests.h> +#include <math-barriers.h> static int do_test (void) @@ -41,8 +42,28 @@ do_test (void) /* Verify fesetexcept does not cause exception traps. For architectures where setting the exception might result in traps the function should - return a nonzero value. */ - ret = fesetexcept (FE_ALL_EXCEPT); + return a nonzero value. + Also check if the function does not alter the exception mask. */ + { + int exc_before = fegetexcept (); + ret = fesetexcept (FE_ALL_EXCEPT); + int exc_after = fegetexcept (); + if (exc_before != exc_after) + { + puts ("fesetexcept (FE_ALL_EXCEPT) changed the exceptions mask"); + return 1; + } + } + + /* Execute some floating-point operations, since on some CPUs exceptions + triggers a trap only at the next floating-point instruction. */ + volatile double a = 1.0; + volatile double b = a + a; + math_force_eval (b); + volatile long double al = 1.0L; + volatile long double bl = al + al; + math_force_eval (bl); + if (ret == 0) puts ("fesetexcept (FE_ALL_EXCEPT) succeeded"); else if (!EXCEPTION_SET_FORCES_TRAP) @@ -61,5 +82,4 @@ do_test (void) return result; } -#define TEST_FUNCTION do_test () -#include "../test-skeleton.c" +#include <support/test-driver.c> diff --git a/sysdeps/i386/fpu/fesetexcept.c b/sysdeps/i386/fpu/fesetexcept.c index 18949e982a..58f577d93d 100644 --- a/sysdeps/i386/fpu/fesetexcept.c +++ b/sysdeps/i386/fpu/fesetexcept.c @@ -17,15 +17,53 @@ <https://www.gnu.org/licenses/>. */ #include <fenv.h> +#include <ldsodefs.h> int fesetexcept (int excepts) { - fenv_t temp; + /* 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. */ - __asm__ ("fnstenv %0" : "=m" (*&temp)); - temp.__status_word |= excepts & FE_ALL_EXCEPT; - __asm__ ("fldenv %0" : : "m" (*&temp)); + excepts &= FE_ALL_EXCEPT; + + if (CPU_FEATURE_USABLE (SSE)) + { + /* Get the control word of the SSE unit. */ + unsigned int mxcsr; + __asm__ ("stmxcsr %0" : "=m" (*&mxcsr)); + + /* Set relevant flags. */ + mxcsr |= excepts; + + /* Put the new data in effect. */ + __asm__ ("ldmxcsr %0" : : "m" (*&mxcsr)); + } + else + { + fenv_t temp; + + /* Note: fnstenv masks all floating-point exceptions until the fldenv + or fldcw below. */ + __asm__ ("fnstenv %0" : "=m" (*&temp)); + + /* Set relevant flags. */ + temp.__status_word |= excepts; + + if ((~temp.__control_word) & excepts) + { + /* Setting the exception flags may trigger a trap (at the next + floating-point instruction, but that does not matter). + ISO C23 (7.6.4.4) does not allow it. */ + __asm__ volatile ("fldcw %0" : : "m" (*&temp.__control_word)); + return -1; + } + + /* Store the new status word (along with the rest of the environment). */ + __asm__ ("fldenv %0" : : "m" (*&temp)); + } return 0; } diff --git a/sysdeps/i386/fpu/math-tests-trap-force.h b/sysdeps/i386/fpu/math-tests-trap-force.h new file mode 100644 index 0000000000..f41e1ffc2d --- /dev/null +++ b/sysdeps/i386/fpu/math-tests-trap-force.h @@ -0,0 +1,29 @@ +/* Configuration for math tests: support for setting exception flags + without causing enabled traps. i686 version. + Copyright (C) 2023 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 + <https://www.gnu.org/licenses/>. */ + +#ifndef I386_FPU_MATH_TESTS_TRAP_FORCE_H +#define I386_FPU_MATH_TESTS_TRAP_FORCE_H 1 + +#include <cpu-features.h> + +/* Setting exception flags in FPU Status Register results in enabled traps for + those exceptions being taken. */ +#define EXCEPTION_SET_FORCES_TRAP !CPU_FEATURE_USABLE (SSE) + +#endif /* math-tests-trap-force.h. */ diff --git a/sysdeps/x86/fpu/test-fenv-sse-2.c b/sysdeps/x86/fpu/test-fenv-sse-2.c index f3e820b6ed..7a0503790f 100644 --- a/sysdeps/x86/fpu/test-fenv-sse-2.c +++ b/sysdeps/x86/fpu/test-fenv-sse-2.c @@ -22,17 +22,8 @@ #include <stdbool.h> #include <stdint.h> #include <stdio.h> - -static bool -have_sse2 (void) -{ - unsigned int eax, ebx, ecx, edx; - - if (!__get_cpuid (1, &eax, &ebx, &ecx, &edx)) - return false; - - return (edx & bit_SSE2) != 0; -} +#include <cpu-features.h> +#include <support/check.h> static uint32_t get_sse_mxcsr (void) @@ -164,13 +155,9 @@ sse_tests (void) static int do_test (void) { - if (!have_sse2 ()) - { - puts ("CPU does not support SSE2, cannot test"); - return 0; - } + if (!CPU_FEATURE_USABLE (SSE2)) + FAIL_UNSUPPORTED ("CPU does not support SSE2"); return sse_tests (); } -#define TEST_FUNCTION do_test () -#include <test-skeleton.c> +#include <support/test-driver.c>