[PATCH v2] i686: Compile .op files and gmon tests with -mfentry

[H.J. Lu]

On Fri, Sep 5, 2025 at 9:02 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On i686, after GCC 16 commit:
>
> commit 07d8de9174c421d719649639a1452b8b9f2eee32
> Author: H.J. Lu <hjl.tools@gmail.com>
> Date:   Wed Jul 2 08:58:23 2025 +0800
>
>     x86-64: Add --enable-x86-64-mfentry
>
> which warns ‘-pg’ without ‘-mfentry’, when glibc is configured with
> --disable-default-pie, GCC 16 fails to compile .op files and gmon tests
> with error:
>
> cc1: error: ‘-pg’ without ‘-mfentry’ may be unreliable with shrink wrapping [-Werror]
>
> Compile .op files and gmon tests with -mfentry if it is supported by
> TEST_CC and glibc is configured with --disable-default-pie.  This fixes
> BZ #33376.

Joseph,  can you review this?  Thanks.

> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> ---
>  sysdeps/i386/Makefile     | 13 ++++++++
>  sysdeps/i386/configure    | 62 +++++++++++++++++++++++++++++++++++++++
>  sysdeps/i386/configure.ac | 14 +++++++++
>  3 files changed, 89 insertions(+)
>
> diff --git a/sysdeps/i386/Makefile b/sysdeps/i386/Makefile
> index 4fbaaa252b..4f96f8e191 100644
> --- a/sysdeps/i386/Makefile
> +++ b/sysdeps/i386/Makefile
> @@ -15,6 +15,13 @@ endif
>
>  ifeq ($(subdir),gmon)
>  sysdep_routines += i386-mcount
> +ifeq ($(build-pie-default)$(have-test-cc-cflags-mfentry),noyes)
> +# Compile with -mfentry to avoid GCC 16 error:
> +# cc1: error: ‘-pg’ without ‘-mfentry’ may be unreliable with shrink wrapping [-Werror]
> +CFLAGS-tst-gmon.c += -mfentry
> +CFLAGS-tst-mcleanup.c += -mfentry
> +CFLAGS-tst-mcount-overflow.c += -mfentry
> +endif
>  endif
>
>  ifeq ($(subdir),csu)
> @@ -63,3 +70,9 @@ generated += check-gnu-tls.out
>  else
>  CFLAGS-.os += $(if $(filter rtld-%.os,$(@F)), $(rtld-CFLAGS))
>  endif
> +
> +ifeq ($(build-pie-default)$(build-profile)$(have-cc-cflags-mfentry),noyesyes)
> +# Compile .op files with -mfentry to avoid GCC 16 error:
> +# cc1: error: ‘-pg’ without ‘-mfentry’ may be unreliable with shrink wrapping [-Werror]
> +CFLAGS-.op += -mfentry
> +endif
> diff --git a/sysdeps/i386/configure b/sysdeps/i386/configure
> index a618692adf..71c334bf0d 100644
> --- a/sysdeps/i386/configure
> +++ b/sysdeps/i386/configure
> @@ -95,3 +95,65 @@ if test x"$multi_arch" != xno; then
>
>  fi
>
> +
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking -mfentry" >&5
> +printf %s "checking -mfentry... " >&6; }
> +if test ${libc_cv_cc_cflags_mfentry+y}
> +then :
> +  printf %s "(cached) " >&6
> +else case e in #(
> +  e) if { ac_try='${CC-cc} -Werror -mfentry -xc /dev/null -S -o /dev/null'
> +  { { 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 $ac_status = 0; }; }
> +then :
> +  libc_cv_cc_cflags_mfentry=yes
> +else case e in #(
> +  e) libc_cv_cc_cflags_mfentry=no ;;
> +esac
> +fi ;;
> +esac
> +fi
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_cv_cc_cflags_mfentry" >&5
> +printf "%s\n" "$libc_cv_cc_cflags_mfentry" >&6; }
> +if test "$TEST_CC" = "$CC"; then
> +  libc_cv_test_cc_cflags_mfentry=$libc_cv_cc_cflags_mfentry
> +else
> +
> +saved_CC="$CC"
> +CC="$TEST_CC"
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking -mfentry in testing" >&5
> +printf %s "checking -mfentry in testing... " >&6; }
> +if test ${libc_cv_test_cc_cflags_mfentry+y}
> +then :
> +  printf %s "(cached) " >&6
> +else case e in #(
> +  e) if { ac_try='${CC-cc} -Werror -mfentry -xc /dev/null -S -o /dev/null'
> +  { { 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 $ac_status = 0; }; }
> +then :
> +  libc_cv_test_cc_cflags_mfentry=yes
> +else case e in #(
> +  e) libc_cv_test_cc_cflags_mfentry=no
> + ;;
> +esac
> +fi ;;
> +esac
> +fi
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_cv_test_cc_cflags_mfentry" >&5
> +printf "%s\n" "$libc_cv_test_cc_cflags_mfentry" >&6; }
> +
> +CC="$saved_CC"
> +
> +fi
> +
> +config_vars="$config_vars
> +have-cc-cflags-mfentry = $libc_cv_cc_cflags_mfentry"
> +config_vars="$config_vars
> +have-test-cc-cflags-mfentry = $libc_cv_test_cc_cflags_mfentry"
> +
> diff --git a/sysdeps/i386/configure.ac b/sysdeps/i386/configure.ac
> index 7f68e6210a..4d2850184b 100644
> --- a/sysdeps/i386/configure.ac
> +++ b/sysdeps/i386/configure.ac
> @@ -63,3 +63,17 @@ dnl via PIC PLT in PIE, which requires setting up EBX register.
>  if test x"$multi_arch" != xno; then
>    AC_DEFINE(NO_HIDDEN_EXTERN_FUNC_IN_PIE)
>  fi
> +
> +dnl Check if CC and TEST_CC support -mfentry.
> +LIBC_TRY_CC_AND_TEST_CC_OPTION([-mfentry],
> +  [-Werror -mfentry],
> +  libc_cv_cc_cflags_mfentry,
> +  [libc_cv_cc_cflags_mfentry=yes],
> +  [libc_cv_cc_cflags_mfentry=no],
> +  libc_cv_test_cc_cflags_mfentry,
> +  [libc_cv_test_cc_cflags_mfentry=yes],
> +  [libc_cv_test_cc_cflags_mfentry=no]
> +)
> +LIBC_CONFIG_VAR(have-cc-cflags-mfentry, $libc_cv_cc_cflags_mfentry)
> +LIBC_CONFIG_VAR(have-test-cc-cflags-mfentry,
> +               $libc_cv_test_cc_cflags_mfentry)
> --
> 2.51.0
>


-- 
H.J.