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

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

On Mon, Jan 8, 2024 at 7:24 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> 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.

I will check it in later today.

-- 
H.J.