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* [glibc] powerpc: Do not raise exception traps for fesetexcept/fesetexceptflag (BZ 30988)
@ 2023-12-19 18:35 Adhemerval Zanella
0 siblings, 0 replies; only message in thread
From: Adhemerval Zanella @ 2023-12-19 18:35 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ecb1e7220ddc7a4845bbd1b6fd7fcf17aba566bd
commit ecb1e7220ddc7a4845bbd1b6fd7fcf17aba566bd
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Tue Oct 24 08:37:14 2023 -0300
powerpc: Do not raise exception traps for fesetexcept/fesetexceptflag (BZ 30988)
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).
This is a side-effect of how we implement the GNU extension
feenableexcept, where feenableexcept/fesetenv/fesetmode/feupdateenv
might issue prctl (PR_SET_FPEXC, PR_FP_EXC_PRECISE) depending of the
argument. And on PR_FP_EXC_PRECISE, setting a floating-point exception
flag triggers a trap.
To make the both functions follow the C23, fesetexcept and
fesetexceptflag now fail if the argument may trigger a trap.
The math tests now check for an value different than 0, instead
of bail out as unsupported for EXCEPTION_SET_FORCES_TRAP.
Checked on powerpc64le-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Diff:
---
math/test-fesetexcept-traps.c | 24 ++++++++++++++++--------
math/test-fexcept-traps.c | 16 +++++++++-------
sysdeps/powerpc/fpu/fesetexcept.c | 5 +++++
sysdeps/powerpc/fpu/fsetexcptflg.c | 9 ++++++++-
4 files changed, 38 insertions(+), 16 deletions(-)
diff --git a/math/test-fesetexcept-traps.c b/math/test-fesetexcept-traps.c
index 71b6e45b33..7efcd0343a 100644
--- a/math/test-fesetexcept-traps.c
+++ b/math/test-fesetexcept-traps.c
@@ -39,16 +39,24 @@ do_test (void)
return result;
}
- if (EXCEPTION_SET_FORCES_TRAP)
- {
- puts ("setting exceptions traps, cannot test on this architecture");
- return 77;
- }
- /* Verify fesetexcept does not cause exception traps. */
+ /* 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);
+
+ _Static_assert (!(EXCEPTION_SET_FORCES_TRAP && !EXCEPTION_TESTS(float)),
+ "EXCEPTION_SET_FORCES_TRAP only makes sense if the "
+ "architecture suports exceptions");
+
if (ret == 0)
- puts ("fesetexcept (FE_ALL_EXCEPT) succeeded");
- else
+ {
+ if (EXCEPTION_SET_FORCES_TRAP)
+ {
+ puts ("unexpected fesetexcept success");
+ result = 1;
+ }
+ }
+ else if (!EXCEPTION_SET_FORCES_TRAP)
{
puts ("fesetexcept (FE_ALL_EXCEPT) failed");
if (EXCEPTION_TESTS (float))
diff --git a/math/test-fexcept-traps.c b/math/test-fexcept-traps.c
index 9701c3c320..998c241058 100644
--- a/math/test-fexcept-traps.c
+++ b/math/test-fexcept-traps.c
@@ -63,14 +63,16 @@ do_test (void)
result = 1;
}
- if (EXCEPTION_SET_FORCES_TRAP)
- {
- puts ("setting exceptions traps, cannot test on this architecture");
- return 77;
- }
- /* The test is that this does not cause exception traps. */
+ /* 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);
- if (ret != 0)
+
+ _Static_assert (!(EXCEPTION_SET_FORCES_TRAP && !EXCEPTION_TESTS(float)),
+ "EXCEPTION_SET_FORCES_TRAP only makes sense if the "
+ "architecture suports exceptions");
+
+ if (ret != 0 && !EXCEPTION_SET_FORCES_TRAP)
{
puts ("fesetexceptflag failed");
result = 1;
diff --git a/sysdeps/powerpc/fpu/fesetexcept.c b/sysdeps/powerpc/fpu/fesetexcept.c
index 609a148a95..2850156d3a 100644
--- a/sysdeps/powerpc/fpu/fesetexcept.c
+++ b/sysdeps/powerpc/fpu/fesetexcept.c
@@ -31,6 +31,11 @@ fesetexcept (int excepts)
& FE_INVALID_SOFTWARE));
if (n.l != u.l)
{
+ if (n.l & fenv_exceptions_to_reg (excepts))
+ /* Setting the exception flags may trigger a trap. ISO C 23 § 7.6.4.4
+ does not allow it. */
+ return -1;
+
fesetenv_register (n.fenv);
/* Deal with FE_INVALID_SOFTWARE not being implemented on some chips. */
diff --git a/sysdeps/powerpc/fpu/fsetexcptflg.c b/sysdeps/powerpc/fpu/fsetexcptflg.c
index 2b22f913c0..6517e8ea03 100644
--- a/sysdeps/powerpc/fpu/fsetexcptflg.c
+++ b/sysdeps/powerpc/fpu/fsetexcptflg.c
@@ -44,7 +44,14 @@ __fesetexceptflag (const fexcept_t *flagp, int excepts)
This may cause floating-point exceptions if the restored state
requests it. */
if (n.l != u.l)
- fesetenv_register (n.fenv);
+ {
+ if (n.l & fenv_exceptions_to_reg (excepts))
+ /* Setting the exception flags may trigger a trap. ISO C 23 § 7.6.4.4
+ does not allow it. */
+ return -1;
+
+ fesetenv_register (n.fenv);
+ }
/* Deal with FE_INVALID_SOFTWARE not being implemented on some chips. */
if (flag & FE_INVALID)
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2023-12-19 18:35 [glibc] powerpc: Do not raise exception traps for fesetexcept/fesetexceptflag (BZ 30988) Adhemerval Zanella
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