[PATCH] i386: Fix fmod/fmof/remainder/remainderf for gcc-12
H.J. Lu
hjl.tools@gmail.com
Fri Nov 21 00:01:50 GMT 2025
On Fri, Nov 21, 2025 at 7:23 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Thu, Nov 20, 2025 at 8:21 PM Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
> >
> > The __builtin_fmod{f} and __builtin_remainder{f} were added on gcc 13,
> > and the minimum supported gcc is 12. This patch adds a configure test
> > to check whether the compiler enables inlining for fmod/remainder, and
> > uses inline assembly if not.
> >
> > Checked on i686-linux-gnu wih gcc-12.
> > ---
> > config.h.in | 3 +++
> > sysdeps/i386/fpu/e_fmod.c | 14 ++++++++++
> > sysdeps/i386/fpu/e_fmodf.c | 14 ++++++++++
> > sysdeps/i386/fpu/e_remainder.c | 14 ++++++++++
> > sysdeps/i386/fpu/e_remainderf.c | 14 ++++++++++
> > sysdeps/x86/configure | 48 +++++++++++++++++++++++++++++++++
> > sysdeps/x86/configure.ac | 27 +++++++++++++++++++
> > 7 files changed, 134 insertions(+)
> >
> > diff --git a/config.h.in b/config.h.in
> > index a7cc17df8e..bfcd29bcdf 100644
> > --- a/config.h.in
> > +++ b/config.h.in
> > @@ -317,6 +317,9 @@
> > /* Define if trunc is inlined on x86. */
> > #undef HAVE_X86_INLINE_TRUNC
> >
> > +/* Define if __builtin_fmod/__builtin_remainder is inlined on x86. */
> > +#undef HAVE_X86_INLINE_FMOD
> > +
> > /* Define if compiler allows add attribute after function declaration. */
> > #undef ATTR_AFTER_FUNC_DECL
> >
> > diff --git a/sysdeps/i386/fpu/e_fmod.c b/sysdeps/i386/fpu/e_fmod.c
> > index 281b23dffc..93b6f9d698 100644
> > --- a/sysdeps/i386/fpu/e_fmod.c
> > +++ b/sysdeps/i386/fpu/e_fmod.c
> > @@ -33,7 +33,21 @@ __fmod (double x, double y)
> > && !is_nan (hx)))
> > return __math_invalid (x);
> >
> > +#if HAVE_X86_INLINE_FMOD
>
> Does __has_builtin (__builtin_fmod) work? Can you define
> __builtin_fmod in x86/fpu/math-inline-asm.h
__has_builtin (__builtin_fmod) doesn't work since GCC 12 just
calls the C function. But it is still a good idea to put them in
x86/fpu/math-inline-asm.h.
> if __has_builtin (__builtin_fmod) is false?
>
> > return __builtin_fmod (x, y);
> > +#else
> > + double result;
> > + asm ("1:\n"
> > + "fprem\n"
> > + "fnstsw %%ax\n"
> > + "sahf\n"
> > + "jp 1b\n"
> > + : "=t" (result)
> > + : "0" (x), "u" (y)
> > + : "ax", "cc"
> > + );
> > + return result;
> > +#endif
> > }
> > strong_alias (__fmod, __ieee754_fmod)
> > libm_alias_finite (__ieee754_fmod, __fmod)
> > diff --git a/sysdeps/i386/fpu/e_fmodf.c b/sysdeps/i386/fpu/e_fmodf.c
> > index 5b05d0fd95..e94ef89534 100644
> > --- a/sysdeps/i386/fpu/e_fmodf.c
> > +++ b/sysdeps/i386/fpu/e_fmodf.c
> > @@ -33,7 +33,21 @@ __fmodf (float x, float y)
> > && !is_nan (hx)))
> > return __math_invalidf (x);
> >
> > +#if HAVE_X86_INLINE_FMOD
> > return __builtin_fmodf (x, y);
> > +#else
> > + float result;
> > + asm ("1:\n"
> > + "fprem\n"
> > + "fnstsw %%ax\n"
> > + "sahf\n"
> > + "jp 1b\n"
> > + : "=t" (result)
> > + : "0" (x), "u" (y)
> > + : "ax", "cc"
> > + );
> > + return result;
> > +#endif
> > }
> > strong_alias (__fmodf, __ieee754_fmodf)
> > versioned_symbol (libm, __fmodf, fmodf, GLIBC_2_43);
> > diff --git a/sysdeps/i386/fpu/e_remainder.c b/sysdeps/i386/fpu/e_remainder.c
> > index ec907ecaf9..4c3be1165a 100644
> > --- a/sysdeps/i386/fpu/e_remainder.c
> > +++ b/sysdeps/i386/fpu/e_remainder.c
> > @@ -33,7 +33,21 @@ __remainder (double x, double y)
> > && !is_nan (hx)))
> > return __math_invalid (x);
> >
> > +#if HAVE_X86_INLINE_FMOD
> > return __builtin_remainder (x, y);
> > +#else
> > + double result;
> > + asm ("1:\n"
> > + "fprem1\n"
> > + "fnstsw %%ax\n"
> > + "sahf\n"
> > + "jp 1b\n"
> > + : "=t" (result)
> > + : "0" (x), "u" (y)
> > + : "ax", "cc"
> > + );
> > + return result;
> > +#endif
> > }
> > strong_alias (__remainder, __ieee754_remainder)
> > versioned_symbol (libm, __remainder, remainder, GLIBC_2_43);
> > diff --git a/sysdeps/i386/fpu/e_remainderf.c b/sysdeps/i386/fpu/e_remainderf.c
> > index 30ca4d3600..e725f892cf 100644
> > --- a/sysdeps/i386/fpu/e_remainderf.c
> > +++ b/sysdeps/i386/fpu/e_remainderf.c
> > @@ -33,7 +33,21 @@ __remainderf (float x, float y)
> > && !is_nan (hx)))
> > return __math_invalidf (x);
> >
> > +#if HAVE_X86_INLINE_FMOD
> > return __builtin_remainderf (x, y);
> > +#else
> > + float result;
> > + asm ("1:\n"
> > + "fprem1\n"
> > + "fnstsw %%ax\n"
> > + "sahf\n"
> > + "jp 1b\n"
> > + : "=t" (result)
> > + : "0" (x), "u" (y)
> > + : "ax", "cc"
> > + );
> > + return result;
> > +#endif
> > }
> > strong_alias (__remainderf, __ieee754_remainderf)
> > versioned_symbol (libm, __remainderf, remainderf, GLIBC_2_43);
> > diff --git a/sysdeps/x86/configure b/sysdeps/x86/configure
> > index e530a18f54..0798f194b6 100644
> > --- a/sysdeps/x86/configure
> > +++ b/sysdeps/x86/configure
> > @@ -430,6 +430,54 @@ else
> >
> > fi
> >
> > +conftest_code="
> > +double foo (double x, double y)
> > +{
> > + return __builtin_fmod (x, y);
> > +}
> > +"
> > +
> > +cat > conftest.c <<EOF
> > +$conftest_code
> > +EOF
> > +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking if compiler inlines __builtin_fmod/__builtin_remainder" >&5
> > +printf %s "checking if compiler inlines __builtin_fmod/__builtin_remainder... " >&6; }
> > +if test ${libc_cv_cc_x86_inline_fmod+y}
> > +then :
> > + printf %s "(cached) " >&6
> > +else case e in #(
> > + e) if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $CFLAGS -fno-math-errno -S conftest.c -o conftest 1>&5'
> > + { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> > + (eval $ac_try) 2>&5
> > + ac_status=$?
> > + printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> > + test $ac_status = 0; }; }
> > + then
> > +
> > +libc_cv_cc_x86_inline_fmod=no
> > +if grep -E -q "fprem" conftest; then
> > + libc_cv_cc_x86_inline_fmod=yes
> > +fi
> > +
> > + else
> > +
> > +echo "failed to check if CC inlines fmod."
> > +rm -f conftest*
> > +exit 1
> > +
> > + fi ;;
> > +esac
> > +fi
> > +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_cv_cc_x86_inline_fmod" >&5
> > +printf "%s\n" "$libc_cv_cc_x86_inline_fmod" >&6; }
> > +rm -f conftest*
> > +if test "$libc_cv_cc_x86_inline_fmod" = yes; then
> > + printf "%s\n" "#define HAVE_X86_INLINE_FMOD 1" >>confdefs.h
> > +
> > +else
> > + printf "%s\n" "#define HAVE_X86_INLINE_FMOD 0" >>confdefs.h
> > +
> > +fi
> >
> > if test "${libc_cv_cc_no_direct_extern_access}${libc_cv_test_cc_cflags_no_direct_extern_access}" = yes; then
> > libc_cv_protected_data=no
> > diff --git a/sysdeps/x86/configure.ac b/sysdeps/x86/configure.ac
> > index c440b6bf5c..1e9c4d86db 100644
> > --- a/sysdeps/x86/configure.ac
> > +++ b/sysdeps/x86/configure.ac
> > @@ -240,6 +240,33 @@ else
> > AC_DEFINE(HAVE_X86_LIBGCC_CMP_RETURN_ATTR, 0)
> > fi
> >
> > +conftest_code="
> > +double foo (double x, double y)
> > +{
> > + return __builtin_fmod (x, y);
> > +}
> > +"
> > +dnl Check if CC inlines __builtin_fmod/__builtin_remainder
> > +LIBC_TRY_CC_COMMAND([if compiler inlines __builtin_fmod/__builtin_remainder],
> > + [$conftest_code],
> > + [$CFLAGS -fno-math-errno -S],
> > + libc_cv_cc_x86_inline_fmod,
> > + [
> > +libc_cv_cc_x86_inline_fmod=no
> > +if grep -E -q "fprem" conftest; then
> > + libc_cv_cc_x86_inline_fmod=yes
> > +fi
> > +],
> > +[
> > +echo "failed to check if CC inlines fmod."
> > +rm -f conftest*
> > +exit 1
> > +])
> > +if test "$libc_cv_cc_x86_inline_fmod" = yes; then
> > + AC_DEFINE(HAVE_X86_INLINE_FMOD, 1)
> > +else
> > + AC_DEFINE(HAVE_X86_INLINE_FMOD, 0)
> > +fi
> >
> > dnl If the building compiler enables no direct external data access by
> > dnl default, access to protected data in shared libraries from executables
> > --
> > 2.43.0
> >
>
>
> --
> H.J.
--
H.J.
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