Fix i386 FP_TRAPPING_EXCEPTIONS

Joseph S. Myers joseph@codesourcery.com
Wed Sep 17 19:47:00 GMT 2014


The i386 sfp-machine.h defines FP_TRAPPING_EXCEPTIONS in a way that is
always wrong: it treats a set bit as indicating the exception is
trapping, when actually a set bit (both for 387 and SSE floating
point) indicates it is masked, and a clear bit indicates it is
trapping.  This patch fixes this bug.

Bootstrapped with no regressions on x86_64-unknown-linux-gnu.  OK to
commit?

Note to ia64 maintainers: it would be a good idea to add a definition
of FP_TRAPPING_EXCEPTIONS for ia64, and I expect the new test to fail
on ia64 until you do so.

libgcc:
2014-09-17  Joseph Myers  <joseph@codesourcery.com>

	* config/i386/sfp-machine.h (FP_TRAPPING_EXCEPTIONS): Treat clear
	bits not set bits as indicating trapping exceptions.

gcc/testsuite:
2014-09-17  Joseph Myers  <joseph@codesourcery.com>

	* gcc.dg/torture/float128-exact-underflow.c: New test.

Index: gcc/testsuite/gcc.dg/torture/float128-exact-underflow.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/float128-exact-underflow.c	(revision 0)
+++ gcc/testsuite/gcc.dg/torture/float128-exact-underflow.c	(revision 0)
@@ -0,0 +1,41 @@
+/* Test that exact underflow in __float128 signals the underflow
+   exception if trapping is enabled, but does not raise the flag
+   otherwise.  */
+
+/* { dg-do run { target i?86-*-*gnu* x86_64-*-*gnu* ia64-*-*gnu* } } */
+/* { dg-options "-D_GNU_SOURCE" } */
+/* { dg-require-effective-target fenv_exceptions } */
+
+#include <fenv.h>
+#include <setjmp.h>
+#include <signal.h>
+#include <stdlib.h>
+
+volatile sig_atomic_t caught_sigfpe;
+sigjmp_buf buf;
+
+static void
+handle_sigfpe (int sig)
+{
+  caught_sigfpe = 1;
+  siglongjmp (buf, 1);
+}
+
+int
+main (void)
+{
+  volatile __float128 a = 0x1p-16382q, b = 0x1p-2q;
+  volatile __float128 r;
+  r = a * b;
+  if (fetestexcept (FE_UNDERFLOW))
+    abort ();
+  if (r != 0x1p-16384q)
+    abort ();
+  feenableexcept (FE_UNDERFLOW);
+  signal (SIGFPE, handle_sigfpe);
+  if (sigsetjmp (buf, 1) == 0)
+    r = a * b;
+  if (!caught_sigfpe)
+    abort ();
+  exit (0);
+}
Index: libgcc/config/i386/sfp-machine.h
===================================================================
--- libgcc/config/i386/sfp-machine.h	(revision 215323)
+++ libgcc/config/i386/sfp-machine.h	(working copy)
@@ -60,7 +60,7 @@
       __sfp_handle_exceptions (_fex);		\
   } while (0);
 
-#define FP_TRAPPING_EXCEPTIONS ((_fcw >> FP_EX_SHIFT) & FP_EX_ALL)
+#define FP_TRAPPING_EXCEPTIONS ((~_fcw >> FP_EX_SHIFT) & FP_EX_ALL)
 
 #define FP_ROUNDMODE		(_fcw & FP_RND_MASK)
 #endif

-- 
Joseph S. Myers
joseph@codesourcery.com



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