Re: [PATCH 3/3] math: math: x86 trunc traps when FE_INEXACT is enabled (BZ 31603)

["H.J. Lu" <hjl.tools@gmail.com>]

On Wed, Apr 3, 2024 at 12:39 PM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
> The implementations of trunc functions using x87 floating point (i386 and
> x86_64 long double only) traps when FE_INEXACT is enabled.  Although
> this is a GNU extension outside the scope of the C standard, other
> architectures that also support traps do not show this behavior.
>
> The fix moves the implementation to a common one that holds any
> exceptions with a 'fnclex' (libc_feholdexcept_setround_387).
>
> Checked on x86_64-linux-gnu and i686-linux-gnu.
> ---
>  math/Makefile                                 |  2 +
>  math/test-trunc-except-2.c                    | 67 +++++++++++++++++++
>  sysdeps/i386/fpu/{s_trunc.S => s_trunc.c}     | 24 ++-----
>  sysdeps/i386/fpu/{s_truncf.S => s_truncf.c}   | 24 ++-----
>  sysdeps/i386/fpu/s_truncl.S                   | 40 -----------
>  .../fpu/s_truncl.S => x86/fpu/s_truncl.c}     | 23 ++-----
>  6 files changed, 87 insertions(+), 93 deletions(-)
>  create mode 100644 math/test-trunc-except-2.c
>  rename sysdeps/i386/fpu/{s_trunc.S => s_trunc.c} (69%)
>  rename sysdeps/i386/fpu/{s_truncf.S => s_truncf.c} (68%)
>  delete mode 100644 sysdeps/i386/fpu/s_truncl.S
>  rename sysdeps/{x86_64/fpu/s_truncl.S => x86/fpu/s_truncl.c} (70%)
>
> diff --git a/math/Makefile b/math/Makefile
> index 121fe2881a..a9fef9e2db 100644
> --- a/math/Makefile
> +++ b/math/Makefile
> @@ -539,6 +539,7 @@ tests = \
>    test-tgmath-int \
>    test-tgmath-ret \
>    test-tgmath2 \
> +  test-trunc-except-2 \
>    tst-CMPLX \
>    tst-CMPLX2 \
>    tst-definitions \
> @@ -993,6 +994,7 @@ CFLAGS-test-nan-const.c += -fno-builtin
>
>  CFLAGS-test-ceil-except-2.c += -fno-builtin
>  CFLAGS-test-floor-except-2.c += -fno-builtin
> +CFLAGS-test-trunc-except-2.c += -fno-builtin
>
>  include ../Rules
>
> diff --git a/math/test-trunc-except-2.c b/math/test-trunc-except-2.c
> new file mode 100644
> index 0000000000..8933c6ab41
> --- /dev/null
> +++ b/math/test-trunc-except-2.c
> @@ -0,0 +1,67 @@
> +/* Test trunc functions do not disable exception traps.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <fenv.h>
> +#include <math.h>
> +#include <stdio.h>
> +
> +#ifndef FE_INEXACT
> +# define FE_INEXACT 0
> +#endif
> +
> +#define TEST_FUNC(NAME, FLOAT, SUFFIX)                                 \
> +static int                                                             \
> +NAME (void)                                                            \
> +{                                                                      \
> +  int result = 0;                                                      \
> +  volatile FLOAT a, b __attribute__ ((unused));                                \
> +  a = 1.5;                                                             \
> +  /* trunc must work when traps on "inexact" are enabled.  */  \
> +  b = trunc ## SUFFIX (a);                                             \
> +  /* And it must have left those traps enabled.  */                    \
> +  if (fegetexcept () == FE_INEXACT)                                    \
> +    puts ("PASS: " #FLOAT);                                            \
> +  else                                                                 \
> +    {                                                                  \
> +      puts ("FAIL: " #FLOAT);                                          \
> +      result = 1;                                                      \
> +    }                                                                  \
> +  return result;                                                       \
> +}
> +
> +TEST_FUNC (float_test, float, f)
> +TEST_FUNC (double_test, double, )
> +TEST_FUNC (ldouble_test, long double, l)
> +
> +static int
> +do_test (void)
> +{
> +  if (feenableexcept (FE_INEXACT) == -1)
> +    {
> +      puts ("enabling FE_INEXACT traps failed, cannot test");
> +      return 77;
> +    }
> +  int result = float_test ();
> +  feenableexcept (FE_INEXACT);
> +  result |= double_test ();
> +  feenableexcept (FE_INEXACT);
> +  result |= ldouble_test ();
> +  return result;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/sysdeps/i386/fpu/s_trunc.S b/sysdeps/i386/fpu/s_trunc.c
> similarity index 69%
> rename from sysdeps/i386/fpu/s_trunc.S
> rename to sysdeps/i386/fpu/s_trunc.c
> index 40e45c9f9c..ac16f4967c 100644
> --- a/sysdeps/i386/fpu/s_trunc.S
> +++ b/sysdeps/i386/fpu/s_trunc.c
> @@ -1,5 +1,5 @@
> -/* Truncate double value.
> -   Copyright (C) 1997-2024 Free Software Foundation, Inc.
> +/* Round to integer, toward zero.  i386 version.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
>     This file is part of the GNU C Library.
>
>     The GNU C Library is free software; you can redistribute it and/or
> @@ -16,22 +16,10 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>
> -#include <machine/asm.h>
>  #include <libm-alias-double.h>
>
> -ENTRY(__trunc)
> -       fldl    4(%esp)
> -       subl    $32, %esp
> -       cfi_adjust_cfa_offset (32)
> -       fnstenv 4(%esp)
> -       movl    $0xc00, %edx
> -       orl     4(%esp), %edx
> -       movl    %edx, (%esp)
> -       fldcw   (%esp)
> -       frndint
> -       fldenv  4(%esp)
> -       addl    $32, %esp
> -       cfi_adjust_cfa_offset (-32)
> -       ret
> -END(__trunc)
> +#define FUNC       __trunc
> +#define TYPE       double
> +#define FE_OPTION  FE_TOWARDZERO
> +#include "s_nearestint_387_template.c"
>  libm_alias_double (__trunc, trunc)
> diff --git a/sysdeps/i386/fpu/s_truncf.S b/sysdeps/i386/fpu/s_truncf.c
> similarity index 68%
> rename from sysdeps/i386/fpu/s_truncf.S
> rename to sysdeps/i386/fpu/s_truncf.c
> index 0b26e09d61..240d3507ef 100644
> --- a/sysdeps/i386/fpu/s_truncf.S
> +++ b/sysdeps/i386/fpu/s_truncf.c
> @@ -1,5 +1,5 @@
> -/* Truncate float value.
> -   Copyright (C) 1997-2024 Free Software Foundation, Inc.
> +/* Round to integer, toward zero.  i386 version.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
>     This file is part of the GNU C Library.
>
>     The GNU C Library is free software; you can redistribute it and/or
> @@ -16,22 +16,10 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>
> -#include <machine/asm.h>
>  #include <libm-alias-float.h>
>
> -ENTRY(__truncf)
> -       flds    4(%esp)
> -       subl    $32, %esp
> -       cfi_adjust_cfa_offset (32)
> -       fnstenv 4(%esp)
> -       movl    $0xc00, %edx
> -       orl     4(%esp), %edx
> -       movl    %edx, (%esp)
> -       fldcw   (%esp)
> -       frndint
> -       fldenv  4(%esp)
> -       addl    $32, %esp
> -       cfi_adjust_cfa_offset (-32)
> -       ret
> -END(__truncf)
> +#define FUNC       __truncf
> +#define TYPE       float
> +#define FE_OPTION  FE_TOWARDZERO
> +#include "s_nearestint_387_template.c"
>  libm_alias_float (__trunc, trunc)
> diff --git a/sysdeps/i386/fpu/s_truncl.S b/sysdeps/i386/fpu/s_truncl.S
> deleted file mode 100644
> index dfd0ca4a57..0000000000
> --- a/sysdeps/i386/fpu/s_truncl.S
> +++ /dev/null
> @@ -1,40 +0,0 @@
> -/* Truncate long double value.
> -   Copyright (C) 1997-2024 Free Software Foundation, Inc.
> -   This file is part of the GNU C Library.
> -
> -   The GNU C Library is free software; you can redistribute it and/or
> -   modify it under the terms of the GNU Lesser General Public
> -   License as published by the Free Software Foundation; either
> -   version 2.1 of the License, or (at your option) any later version.
> -
> -   The GNU C Library is distributed in the hope that it will be useful,
> -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> -   Lesser General Public License for more details.
> -
> -   You should have received a copy of the GNU Lesser General Public
> -   License along with the GNU C Library; if not, see
> -   <https://www.gnu.org/licenses/>.  */
> -
> -#include <libm-alias-ldouble.h>
> -#include <machine/asm.h>
> -
> -ENTRY(__truncl)
> -       fldt    4(%esp)
> -       subl    $32, %esp
> -       cfi_adjust_cfa_offset (32)
> -       fnstenv 4(%esp)
> -       movl    $0xc00, %edx
> -       orl     4(%esp), %edx
> -       movl    %edx, (%esp)
> -       fldcw   (%esp)
> -       frndint
> -       fnstsw
> -       andl    $0x1, %eax
> -       orl     %eax, 8(%esp)
> -       fldenv  4(%esp)
> -       addl    $32, %esp
> -       cfi_adjust_cfa_offset (-32)
> -       ret
> -END(__truncl)
> -libm_alias_ldouble (__trunc, trunc)
> diff --git a/sysdeps/x86_64/fpu/s_truncl.S b/sysdeps/x86/fpu/s_truncl.c
> similarity index 70%
> rename from sysdeps/x86_64/fpu/s_truncl.S
> rename to sysdeps/x86/fpu/s_truncl.c
> index e3d64a84e8..e2bac7fa38 100644
> --- a/sysdeps/x86_64/fpu/s_truncl.S
> +++ b/sysdeps/x86/fpu/s_truncl.c
> @@ -1,5 +1,5 @@
> -/* Truncate long double value.
> -   Copyright (C) 1997-2024 Free Software Foundation, Inc.
> +/* Round to integer, toward zero.  x86 version.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
>     This file is part of the GNU C Library.
>
>     The GNU C Library is free software; you can redistribute it and/or
> @@ -17,20 +17,9 @@
>     <https://www.gnu.org/licenses/>.  */
>
>  #include <libm-alias-ldouble.h>
> -#include <machine/asm.h>
>
> -ENTRY(__truncl)
> -       fldt    8(%rsp)
> -       fnstenv -28(%rsp)
> -       movl    $0xc00, %edx
> -       orl     -28(%rsp), %edx
> -       movl    %edx, -32(%rsp)
> -       fldcw   -32(%rsp)
> -       frndint
> -       fnstsw
> -       andl    $0x1, %eax
> -       orl     %eax, -24(%rsp)
> -       fldenv  -28(%rsp)
> -       ret
> -END(__truncl)
> +#define FUNC       __truncl
> +#define TYPE       long double
> +#define FE_OPTION  FE_TOWARDZERO
> +#include "s_nearestint_387_template.c"
>  libm_alias_ldouble (__trunc, trunc)
> --
> 2.34.1
>

LGTM.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

Thanks.

-- 
H.J.