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authorBruno Haible <bruno@clisp.org>2023-10-24 08:37:16 -0300
committerAdhemerval Zanella <adhemerval.zanella@linaro.org>2023-12-19 15:12:38 -0300
commit787282dede7f134fdb22155cee0c35172e3e28f3 (patch)
treeef7d2a333bd0cf9118f1afd3183186db07ed0513 /math
parent47a9eeb9ba72fd30766bdf4faa7d46b8ca33a7fd (diff)
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x86: Do not raises floating-point exception traps on fesetexceptflag (BZ 30990)
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> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Diffstat (limited to 'math')
-rw-r--r--math/test-fexcept-traps.c23
1 files changed, 22 insertions, 1 deletions
diff --git a/math/test-fexcept-traps.c b/math/test-fexcept-traps.c
index 998c241..ac63fbc 100644
--- a/math/test-fexcept-traps.c
+++ b/math/test-fexcept-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)
@@ -65,12 +66,32 @@ 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. */
+ return a nonzero value.
+ Also check if the function does not alter the exception mask. */
ret = fesetexceptflag (&saved, FE_ALL_EXCEPT);
_Static_assert (!(EXCEPTION_SET_FORCES_TRAP && !EXCEPTION_TESTS(float)),
"EXCEPTION_SET_FORCES_TRAP only makes sense if the "
"architecture suports exceptions");
+ {
+ 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)
{