@@ -19,6 +19,7 @@
#include <fenv.h>
#include <stdio.h>
#include <math-tests.h>
+#include <math-barriers.h>
static int
do_test (void)
@@ -66,7 +67,26 @@ do_test (void)
/* The test is that this does not cause exception traps. For architectures
where setting the exception might result in traps the function should
return a nonzero value. */
- ret = fesetexceptflag (&saved, FE_ALL_EXCEPT);
+ {
+ int exc_before = fegetexcept ();
+ ret = fesetexceptflag (&saved, FE_ALL_EXCEPT);
+ int exc_after = fegetexcept ();
+ if (exc_before != exc_after)
+ {
+ puts ("fesetexceptflag (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 && !EXCEPTION_SET_FORCES_TRAP)
{
puts ("fesetexceptflag failed");
@@ -17,42 +17,63 @@
<https://www.gnu.org/licenses/>. */
#include <fenv.h>
-#include <math.h>
-#include <unistd.h>
#include <ldsodefs.h>
-#include <dl-procinfo.h>
int
__fesetexceptflag (const fexcept_t *flagp, int excepts)
{
- fenv_t temp;
+ /* The flags can be set in the 387 unit or in the SSE unit. When we need to
+ clear a flag, we need to do so in both units, due to the way fetestexcept
+ is implemented.
+ When we need 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. */
- /* Get the current environment. We have to do this since we cannot
- separately set the status word. */
- __asm__ ("fnstenv %0" : "=m" (*&temp));
+ fenv_t temp;
- temp.__status_word &= ~(excepts & FE_ALL_EXCEPT);
- temp.__status_word |= *flagp & excepts & FE_ALL_EXCEPT;
+ excepts &= FE_ALL_EXCEPT;
- /* Store the new status word (along with the rest of the environment.
- Possibly new exceptions are set but they won't get executed unless
- the next floating-point instruction. */
- __asm__ ("fldenv %0" : : "m" (*&temp));
+ /* Get the current x87 FPU environment. We have to do this since we
+ cannot separately set the status word.
+ Note: fnstenv masks all floating-point exceptions until the fldenv
+ or fldcw below. */
+ __asm__ ("fnstenv %0" : "=m" (*&temp));
- /* If the CPU supports SSE, we set the MXCSR as well. */
if (CPU_FEATURE_USABLE (SSE))
{
- unsigned int xnew_exc;
+ unsigned int mxcsr;
+
+ /* Clear relevant flags. */
+ temp.__status_word &= ~(excepts & ~ *flagp);
- /* Get the current MXCSR. */
- __asm__ ("stmxcsr %0" : "=m" (*&xnew_exc));
+ /* Store the new status word (along with the rest of the environment). */
+ __asm__ ("fldenv %0" : : "m" (*&temp));
- /* Set the relevant bits. */
- xnew_exc &= ~(excepts & FE_ALL_EXCEPT);
- xnew_exc |= *flagp & excepts & FE_ALL_EXCEPT;
+ /* And now similarly for SSE. */
+ __asm__ ("stmxcsr %0" : "=m" (*&mxcsr));
+
+ /* Clear or set relevant flags. */
+ mxcsr ^= (mxcsr ^ *flagp) & excepts;
/* Put the new data in effect. */
- __asm__ ("ldmxcsr %0" : : "m" (*&xnew_exc));
+ __asm__ ("ldmxcsr %0" : : "m" (*&mxcsr));
+ }
+ else
+ {
+ /* Clear or set relevant flags. */
+ temp.__status_word ^= (temp.__status_word ^ *flagp) & excepts;
+
+ if ((~temp.__control_word) & temp.__status_word & excepts)
+ {
+ /* Setting the exception flags may trigger a trap (at the next
+ floating-point instruction, but that does not matter).
+ ISO C 23 ยง 7.6.4.5 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));
}
/* Success. */
@@ -22,30 +22,34 @@
int
fesetexceptflag (const fexcept_t *flagp, int excepts)
{
+ /* The flags can be set in the 387 unit or in the SSE unit.
+ When we need to clear a flag, we need to do so in both units,
+ due to the way fetestexcept() is implemented.
+ When we need to set a flag, it is sufficient to do it in the SSE unit,
+ because that is guaranteed to not trap. */
+
fenv_t temp;
unsigned int mxcsr;
- /* XXX: Do we really need to set both the exception in both units?
- Shouldn't it be enough to set only the SSE unit? */
+ excepts &= FE_ALL_EXCEPT;
/* Get the current x87 FPU environment. We have to do this since we
cannot separately set the status word. */
__asm__ ("fnstenv %0" : "=m" (*&temp));
- temp.__status_word &= ~(excepts & FE_ALL_EXCEPT);
- temp.__status_word |= *flagp & excepts & FE_ALL_EXCEPT;
+ /* Clear relevant flags. */
+ temp.__status_word &= ~(excepts & ~ *flagp);
- /* Store the new status word (along with the rest of the environment.
- Possibly new exceptions are set but they won't get executed unless
- the next floating-point instruction. */
+ /* Store the new status word (along with the rest of the environment). */
__asm__ ("fldenv %0" : : "m" (*&temp));
- /* And now the same for SSE. */
+ /* And now similarly for SSE. */
__asm__ ("stmxcsr %0" : "=m" (*&mxcsr));
- mxcsr &= ~(excepts & FE_ALL_EXCEPT);
- mxcsr |= *flagp & excepts & FE_ALL_EXCEPT;
+ /* Clear or set relevant flags. */
+ mxcsr ^= (mxcsr ^ *flagp) & excepts;
+ /* Put the new data in effect. */
__asm__ ("ldmxcsr %0" : : "m" (*&mxcsr));
/* Success. */
From: Bruno Haible <bruno@clisp.org> 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. When we need to clear a flag, we need to do so in both units, due to the way fetestexcept is implemented. When we need 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. Co-authored-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> --- math/test-fexcept-traps.c | 22 ++++++++++- sysdeps/i386/fpu/fsetexcptflg.c | 63 ++++++++++++++++++++----------- sysdeps/x86_64/fpu/fsetexcptflg.c | 24 +++++++----- 3 files changed, 77 insertions(+), 32 deletions(-)