From da09e6fa2f8194fbdd82281195145aec195144dc Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Thu, 11 Jan 2018 18:18:46 +0000 Subject: Make default libc_feholdsetround_noex_ctx use __feholdexcept (bug 22702). For soft-float powerpc, the math/test-nearbyint-except-2 test fails because nearbyintl traps when traps on "inexact" are enabled on entry (and an "inexact" exception is generated internally, though cleared for the final return). The problem is the default implementation of libc_feholdsetround_noex_ctx, which does not disable exception traps. There is some ambiguity about whether the *noex* interfaces are required to do so or only permitted to do so. But given that we support fe* interfaces to enable and disable traps (on architectures with that functionality), functions that must not raise an exception (must not leave the flag set on exit if not set on entry) should also not trap on it when traps on that exception are enabled. So it is appropriate to define these interfaces to have the feholdexcept effect of disabling exception traps; this patch updates the default implementation and comments accordingly. At least some architecture versions already disable traps; there are few uses of the *noex* interfaces at all, and while it's possible there are bugs on any architecture versions failing to disable traps that appear in the exp2 and remainder implementations, there are currently no tests, other than this one for nearbyintl (where only the ldbl-128ibm implementation uses SET_RESTORE_ROUND_NOEX), that would fail as a result of such a bug. (Hard-float powerpc does disable traps here, hence the nearbyintl failure not appearing there.) Tested for powerpc (soft-float). This brings that configuration to clean math/ test results, provided you build with GCC 8 to get the fix for GCC bug 64811. [BZ #22702] * sysdeps/generic/math_private.h (libc_feresetround_noex): Update comment to say exceptions are discarded. (libc_feholdsetround_noex_ctx): Use __feholdexcept instead of __fegetenv. (SET_RESTORE_ROUND_NOEX): Update comment to say non-stop mode must be enabled. --- sysdeps/generic/math_private.h | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) (limited to 'sysdeps/generic/math_private.h') diff --git a/sysdeps/generic/math_private.h b/sysdeps/generic/math_private.h index f29898c19c..e4b9d8697f 100644 --- a/sysdeps/generic/math_private.h +++ b/sysdeps/generic/math_private.h @@ -498,7 +498,7 @@ default_libc_feupdateenv_test (fenv_t *e, int ex) # define libc_feresetroundl libc_feupdateenvl #endif -/* ... and a version that may also discard exceptions. */ +/* ... and a version that also discards exceptions. */ #ifndef libc_feresetround_noex # define libc_feresetround_noex libc_fesetenv @@ -572,8 +572,9 @@ libc_feresetround_ctx (struct rm_ctx *ctx) static __always_inline void libc_feholdsetround_noex_ctx (struct rm_ctx *ctx, int round) { - /* Save exception flags and rounding mode. */ - __fegetenv (&ctx->env); + /* Save exception flags and rounding mode, and disable exception + traps. */ + __feholdexcept (&ctx->env); /* Update rounding mode only if different. */ if (__glibc_unlikely (round != get_rounding_mode ())) @@ -626,7 +627,7 @@ libc_feresetround_noex_ctx (struct rm_ctx *ctx) the value at the start of the block. The exception mode must be preserved. Exceptions raised within the block must be discarded, and exception flags are restored to the value at the start of the block. - Non-stop mode may be enabled inside the block. */ + Non-stop mode must be enabled inside the block. */ #define SET_RESTORE_ROUND_NOEX(RM) \ SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetround_noex, \ -- cgit 1.4.1