Re: [PATCH v2 2/2] ld: Add --enable-mark-plt configure option

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

On Sat, Jan 6, 2024 at 2:10 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> Add --enable-mark-plt linker configure option to mark PLT entries with
> DT_X86_64_PLT, DT_X86_64_PLTSZ and DT_X86_64_PLTENT dynamic tags by
> default.
>
>         * NEWS: Mention -z mark-plt/-z nomark-plt and --enable-mark-plt.
>         * config.in: Regenerated.
>         * configure: Likewise.
>         * configure.ac: Add --enable-mark-plt.
>         (DEFAULT_LD_Z_MARK_PLT): New AC_DEFINE_UNQUOTED.
>         * emulparams/x86-64-plt.sh (PARSE_AND_LIST_OPTIONS_X86_64_PLT):
>         Support DEFAULT_LD_Z_MARK_PLT.
>         * emultempl/elf-x86.em (elf_x86_64_before_parse): New function.
>         (LDEMUL_BEFORE_PARSE): New.  Set to elf_x86_64_before_parse for
>         x86-64 targets.
> ---
>  ld/NEWS                     |  5 +++++
>  ld/config.in                |  4 ++++
>  ld/configure                | 26 ++++++++++++++++++++++++--
>  ld/configure.ac             | 17 +++++++++++++++++
>  ld/emulparams/x86-64-plt.sh |  7 ++++++-
>  ld/emultempl/elf-x86.em     | 17 +++++++++++++++++
>  6 files changed, 73 insertions(+), 3 deletions(-)
>
> diff --git a/ld/NEWS b/ld/NEWS
> index a2c0b7fbcfe..cedd0d72d1b 100644
> --- a/ld/NEWS
> +++ b/ld/NEWS
> @@ -1,5 +1,10 @@
>  -*- text -*-
>
> +* Add -z mark-plt/-z nomark-plt options to x86-64 ELF linker to mark PLT
> +  entries with DT_X86_64_PLT, DT_X86_64_PLTSZ and DT_X86_64_PLTENT dynamic
> +  tags.  Also added --enable-mark-plt configure option to mark PLT entries
> +  by default.
> +
>  * Support Intel APX relocations.
>
>  * On RISC-V, add ld target option --[no-]check-uleb128.  Should rebuild the
> diff --git a/ld/config.in b/ld/config.in
> index 86d90d53752..52d62f06ff0 100644
> --- a/ld/config.in
> +++ b/ld/config.in
> @@ -45,6 +45,10 @@
>     default. */
>  #undef DEFAULT_LD_WARN_RWX_SEGMENTS
>
> +/* Define to 1 if you want to enable -z mark-plt in ELF x86-64 linker by
> +   default. */
> +#undef DEFAULT_LD_Z_MARK_PLT
> +
>  /* Define to 1 if you want to enable -z relro in ELF linker by default. */
>  #undef DEFAULT_LD_Z_RELRO
>
> diff --git a/ld/configure b/ld/configure
> index 07eb669d906..b7f29ca68b7 100755
> --- a/ld/configure
> +++ b/ld/configure
> @@ -852,6 +852,7 @@ enable_new_dtags
>  enable_relro
>  enable_textrel_check
>  enable_separate_code
> +enable_mark_plt
>  enable_warn_execstack
>  enable_error_execstack
>  enable_warn_rwx_segments
> @@ -1546,6 +1547,7 @@ Optional Features:
>    --enable-textrel-check=[yes|no|warning|error]
>                            enable DT_TEXTREL check in ELF linker
>    --enable-separate-code  enable -z separate-code in ELF linker by default
> +  --enable-mark-plt       enable -z mark-plt in ELF x86-64 linker by default
>    --enable-warn-execstack enable warnings when creating an executable stack
>    --enable-error-execstack
>                            turn executable stack warnings into errors
> @@ -11681,7 +11683,7 @@ else
>    lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
>    lt_status=$lt_dlunknown
>    cat > conftest.$ac_ext <<_LT_EOF
> -#line 11684 "configure"
> +#line 11686 "configure"
>  #include "confdefs.h"
>
>  #if HAVE_DLFCN_H
> @@ -11787,7 +11789,7 @@ else
>    lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
>    lt_status=$lt_dlunknown
>    cat > conftest.$ac_ext <<_LT_EOF
> -#line 11790 "configure"
> +#line 11792 "configure"
>  #include "confdefs.h"
>
>  #if HAVE_DLFCN_H
> @@ -15682,6 +15684,17 @@ esac
>  fi
>
>
> +# Decide if -z mark-plt should be enabled in ELF x86-64 linker by default.
> +ac_default_ld_z_mark_plt=unset
> +# Check whether --enable-mark-plt was given.
> +if test "${enable_mark_plt+set}" = set; then :
> +  enableval=$enable_mark_plt; case "${enableval}" in
> +  yes) ac_default_ld_z_mark_plt=1 ;;
> +  no) ac_default_ld_z_mark_plt=0 ;;
> +esac
> +fi
> +
> +
>
>  # By default warn when an executable stack is created due to object files
>  # requesting such, not when the user specifies -z execstack.
> @@ -19365,6 +19378,15 @@ cat >>confdefs.h <<_ACEOF
>  _ACEOF
>
>
> +if test "${ac_default_ld_z_mark_plt}" = unset; then
> +  ac_default_ld_z_mark_plt=0
> +fi
> +
> +cat >>confdefs.h <<_ACEOF
> +#define DEFAULT_LD_Z_MARK_PLT $ac_default_ld_z_mark_plt
> +_ACEOF
> +
> +
>
>
>  cat >>confdefs.h <<_ACEOF
> diff --git a/ld/configure.ac b/ld/configure.ac
> index b46f415fe9b..4a11787ae71 100644
> --- a/ld/configure.ac
> +++ b/ld/configure.ac
> @@ -213,6 +213,16 @@ AC_ARG_ENABLE(separate-code,
>    no) ac_default_ld_z_separate_code=0 ;;
>  esac])
>
> +# Decide if -z mark-plt should be enabled in ELF x86-64 linker by default.
> +ac_default_ld_z_mark_plt=unset
> +AC_ARG_ENABLE(mark-plt,
> +             AS_HELP_STRING([--enable-mark-plt],
> +             [enable -z mark-plt in ELF x86-64 linker by default]),
> +[case "${enableval}" in
> +  yes) ac_default_ld_z_mark_plt=1 ;;
> +  no) ac_default_ld_z_mark_plt=0 ;;
> +esac])
> +
>
>  # By default warn when an executable stack is created due to object files
>  # requesting such, not when the user specifies -z execstack.
> @@ -562,6 +572,13 @@ AC_DEFINE_UNQUOTED(DEFAULT_LD_Z_SEPARATE_CODE,
>    $ac_default_ld_z_separate_code,
>    [Define to 1 if you want to enable -z separate-code in ELF linker by default.])
>
> +if test "${ac_default_ld_z_mark_plt}" = unset; then
> +  ac_default_ld_z_mark_plt=0
> +fi
> +AC_DEFINE_UNQUOTED(DEFAULT_LD_Z_MARK_PLT,
> +  $ac_default_ld_z_mark_plt,
> +  [Define to 1 if you want to enable -z mark-plt in ELF x86-64 linker by default.])
> +
>
>  AC_DEFINE_UNQUOTED(DEFAULT_LD_WARN_EXECSTACK,
>    $ac_default_ld_warn_execstack,
> diff --git a/ld/emulparams/x86-64-plt.sh b/ld/emulparams/x86-64-plt.sh
> index 92732401dc7..d1a5c65937f 100644
> --- a/ld/emulparams/x86-64-plt.sh
> +++ b/ld/emulparams/x86-64-plt.sh
> @@ -1,5 +1,10 @@
>  PARSE_AND_LIST_OPTIONS_X86_64_PLT='
> -  fprintf (file, _("\
> +  if (DEFAULT_LD_Z_MARK_PLT != 0)
> +    fprintf (file, _("\
> +  -z mark-plt                 Mark PLT with dynamic tags (default)\n\
> +  -z nomark-plt               Do not mark PLT with dynamic tags\n"));
> +  else
> +    fprintf (file, _("\
>    -z mark-plt                 Mark PLT with dynamic tags\n\
>    -z nomark-plt               Do not mark PLT with dynamic tags (default)\n"));
>  '
> diff --git a/ld/emultempl/elf-x86.em b/ld/emultempl/elf-x86.em
> index 0ccad72ab9a..a6eda14253f 100644
> --- a/ld/emultempl/elf-x86.em
> +++ b/ld/emultempl/elf-x86.em
> @@ -56,3 +56,20 @@ EOF
>
>  LDEMUL_BEFORE_PARSE=elf_x86_before_parse
>  fi
> +
> +case x${OUTPUT_FORMAT} in
> +  x*x86-64*)
> +fragment <<EOF
> +
> +static void
> +elf_x86_64_before_parse (void)
> +{
> +  params.mark_plt = DEFAULT_LD_Z_MARK_PLT;
> +
> +  elf_x86_before_parse ();
> +}
> +EOF
> +
> +    LDEMUL_BEFORE_PARSE=elf_x86_64_before_parse
> +    ;;
> +esac
> --
> 2.43.0
>

Any comments?

Thanks.

-- 
H.J.