Oops, this code has a bug on x86_64 and i386: It may leave the exception
traps masked, due to a side effect of the 'fnsetenv' instruction. This
patch should fix it.
2023-10-30 Bruno Haible <br...@clisp.org>
fenv-exceptions-tracking-{c99,c23}: Fix the x86_64 and i386 case.
* lib/fenv-except-tracking-clear.c (feclearexcept): Make sure to restore
the exception trap bits in all cases.
* lib/fenv-except-tracking-raise.c (feraiseexcept): Likewise.
* lib/fenv-except-tracking-set.c (fesetexcept): Likewise.
From 6d2dfab57ddfad6bede47999eced62e517e88efd Mon Sep 17 00:00:00 2001
From: Bruno Haible <br...@clisp.org>
Date: Mon, 30 Oct 2023 16:32:30 +0100
Subject: [PATCH 01/14] fenv-exceptions-tracking-{c99,c23}: Fix the x86_64 and
i386 case.
* lib/fenv-except-tracking-clear.c (feclearexcept): Make sure to restore
the exception trap bits in all cases.
* lib/fenv-except-tracking-raise.c (feraiseexcept): Likewise.
* lib/fenv-except-tracking-set.c (fesetexcept): Likewise.
---
ChangeLog | 8 ++++++++
lib/fenv-except-tracking-clear.c | 7 +++----
lib/fenv-except-tracking-raise.c | 16 ++++++----------
lib/fenv-except-tracking-set.c | 20 +++++++++-----------
4 files changed, 26 insertions(+), 25 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 26686c3fb8..1fc40e4ae2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2023-10-30 Bruno Haible <br...@clisp.org>
+
+ fenv-exceptions-tracking-{c99,c23}: Fix the x86_64 and i386 case.
+ * lib/fenv-except-tracking-clear.c (feclearexcept): Make sure to restore
+ the exception trap bits in all cases.
+ * lib/fenv-except-tracking-raise.c (feraiseexcept): Likewise.
+ * lib/fenv-except-tracking-set.c (fesetexcept): Likewise.
+
2023-10-29 Bruno Haible <br...@clisp.org>
fenv-exceptions-tracking-c23: Add tests.
diff --git a/lib/fenv-except-tracking-clear.c b/lib/fenv-except-tracking-clear.c
index 22c85c98e0..9819832a5f 100644
--- a/lib/fenv-except-tracking-clear.c
+++ b/lib/fenv-except-tracking-clear.c
@@ -48,12 +48,11 @@ feclearexcept (int exceptions)
/* Clear the bits in the 387 unit. */
x86_387_fenv_t env;
- unsigned short orig_status_word;
__asm__ __volatile__ ("fnstenv %0" : "=m" (*&env));
- orig_status_word = env.__status_word;
+ /* Note: fnstenv masks all floating-point exceptions until the fldenv
+ below. */
env.__status_word &= ~exceptions;
- if (env.__status_word != orig_status_word)
- __asm__ __volatile__ ("fldenv %0" : : "m" (*&env));
+ __asm__ __volatile__ ("fldenv %0" : : "m" (*&env));
if (CPU_HAS_SSE ())
{
diff --git a/lib/fenv-except-tracking-raise.c b/lib/fenv-except-tracking-raise.c
index 8699662ef5..c263151e60 100644
--- a/lib/fenv-except-tracking-raise.c
+++ b/lib/fenv-except-tracking-raise.c
@@ -106,18 +106,14 @@ feraiseexcept (int exceptions)
/* Set the bits in the 387 unit. */
x86_387_fenv_t env;
- unsigned short orig_status_word;
__asm__ __volatile__ ("fnstenv %0" : "=m" (*&env));
- orig_status_word = env.__status_word;
+ /* Note: fnstenv masks all floating-point exceptions until the fldenv
+ below. */
env.__status_word |= exceptions;
- if (env.__status_word != orig_status_word)
- {
- __asm__ __volatile__ ("fldenv %0" : : "m" (*&env));
- /* A trap (if enabled) is triggered only at the next floating-point
- instruction. Force it to occur here. */
- __asm__ __volatile__ ("fwait");
- }
-
+ __asm__ __volatile__ ("fldenv %0" : : "m" (*&env));
+ /* A trap (if enabled) is triggered only at the next floating-point
+ instruction. Force it to occur here. */
+ __asm__ __volatile__ ("fwait");
}
# endif
diff --git a/lib/fenv-except-tracking-set.c b/lib/fenv-except-tracking-set.c
index 73b566cb01..d4237015e8 100644
--- a/lib/fenv-except-tracking-set.c
+++ b/lib/fenv-except-tracking-set.c
@@ -69,21 +69,19 @@ fesetexcept (int exceptions)
{
/* Set the flags in the 387 unit. */
x86_387_fenv_t env;
- unsigned short orig_status_word;
__asm__ __volatile__ ("fnstenv %0" : "=m" (*&env));
- orig_status_word = env.__status_word;
+ /* Note: fnstenv masks all floating-point exceptions until the fldenv
+ or fldcw below. */
env.__status_word |= exceptions;
- if (env.__status_word != orig_status_word)
+ if ((~env.__control_word) & exceptions)
{
- if ((~env.__control_word) & exceptions)
- {
- /* Setting the exception flags may trigger a trap (at the next
- floating-point instruction, but that does not matter).
- ISO C 23 § 7.6.4.4 does not allow it. */
- return -1;
- }
- __asm__ __volatile__ ("fldenv %0" : : "m" (*&env));
+ /* Setting the exception flags may trigger a trap (at the next
+ floating-point instruction, but that does not matter).
+ ISO C 23 § 7.6.4.4 does not allow it. */
+ __asm__ __volatile__ ("fldcw %0" : : "m" (*&env.__control_word));
+ return -1;
}
+ __asm__ __volatile__ ("fldenv %0" : : "m" (*&env));
}
# endif
# endif
--
2.34.1
