Re: [PATCH] x86-64: Remove HAVE_LD_PIE_COPYRELOC

["Fāng-ruì Sòng" <maskray@google.com>]

PING^4 https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html

One major design goal of PIE was to avoid copy relocations.
The original patch for GCC 5 caused problems for many years.

On Wed, Aug 18, 2021 at 11:54 PM Fāng-ruì Sòng <maskray@google.com> wrote:

> PING^3 https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html
>
> On Fri, Jun 4, 2021 at 3:04 PM Fāng-ruì Sòng <maskray@google.com> wrote:
> >
> > PING^2 https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html
> >
> > On Mon, May 24, 2021 at 9:43 AM Fāng-ruì Sòng <maskray@google.com>
> wrote:
> > >
> > > Ping https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html
> > >
> > > On Tue, May 11, 2021 at 8:29 PM Fangrui Song <maskray@google.com>
> wrote:
> > > >
> > > > This was introduced in 2014-12 to use local binding for external
> symbols
> > > > for -fPIE. Now that we have H.J. Lu's GOTPCRELX for years which
> mostly
> > > > nullify the benefit of HAVE_LD_PIE_COPYRELOC, HAVE_LD_PIE_COPYRELOC
> > > > should retire now.
> > > >
> > > > One design goal of -fPIE was to avoid copy relocations.
> > > > HAVE_LD_PIE_COPYRELOC has deviated from the goal.  With this change,
> the
> > > > -fPIE behavior of x86-64 will be closer to x86-32 and other targets.
> > > >
> > > > ---
> > > >
> > > > See https://gcc.gnu.org/legacy-ml/gcc/2019-05/msg00215.html for a
> list
> > > > of fixed and unfixed (e.g. gold incompatibility with protected
> > > > https://sourceware.org/bugzilla/show_bug.cgi?id=19823) issues.
> > > >
> > > > If you prefer a longer write-up, see
> > > >
> https://maskray.me/blog/2021-01-09-copy-relocations-canonical-plt-entries-and-protected
> > > > ---
> > > >  gcc/config.in                                 |  6 ---
> > > >  gcc/config/i386/i386.c                        | 11 +---
> > > >  gcc/configure                                 | 52
> -------------------
> > > >  gcc/configure.ac                              | 48
> -----------------
> > > >  gcc/doc/sourcebuild.texi                      |  3 --
> > > >  .../gcc.target/i386/pie-copyrelocs-1.c        | 14 -----
> > > >  .../gcc.target/i386/pie-copyrelocs-2.c        | 14 -----
> > > >  .../gcc.target/i386/pie-copyrelocs-3.c        | 14 -----
> > > >  .../gcc.target/i386/pie-copyrelocs-4.c        | 17 ------
> > > >  gcc/testsuite/lib/target-supports.exp         | 47 -----------------
> > > >  10 files changed, 2 insertions(+), 224 deletions(-)
> > > >  delete mode 100644 gcc/testsuite/gcc.target/i386/pie-copyrelocs-1.c
> > > >  delete mode 100644 gcc/testsuite/gcc.target/i386/pie-copyrelocs-2.c
> > > >  delete mode 100644 gcc/testsuite/gcc.target/i386/pie-copyrelocs-3.c
> > > >  delete mode 100644 gcc/testsuite/gcc.target/i386/pie-copyrelocs-4.c
> > > >
> > > > diff --git a/gcc/config.in b/gcc/config.in
> > > > index e54f59ce0c3..a65bf5d4176 100644
> > > > --- a/gcc/config.in
> > > > +++ b/gcc/config.in
> > > > @@ -1659,12 +1659,6 @@
> > > >  #endif
> > > >
> > > >
> > > > -/* Define 0/1 if your linker supports -pie option with copy reloc.
> */
> > > > -#ifndef USED_FOR_TARGET
> > > > -#undef HAVE_LD_PIE_COPYRELOC
> > > > -#endif
> > > > -
> > > > -
> > > >  /* Define if your PowerPC linker has .gnu.attributes long double
> support. */
> > > >  #ifndef USED_FOR_TARGET
> > > >  #undef HAVE_LD_PPC_GNU_ATTR_LONG_DOUBLE
> > > > diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> > > > index 915f89f571a..5ec3c6fd0c9 100644
> > > > --- a/gcc/config/i386/i386.c
> > > > +++ b/gcc/config/i386/i386.c
> > > > @@ -10579,11 +10579,7 @@ legitimate_pic_address_disp_p (rtx disp)
> > > >                 return true;
> > > >             }
> > > >           else if (!SYMBOL_REF_FAR_ADDR_P (op0)
> > > > -                  && (SYMBOL_REF_LOCAL_P (op0)
> > > > -                      || (HAVE_LD_PIE_COPYRELOC
> > > > -                          && flag_pie
> > > > -                          && !SYMBOL_REF_WEAK (op0)
> > > > -                          && !SYMBOL_REF_FUNCTION_P (op0)))
> > > > +                  && SYMBOL_REF_LOCAL_P (op0)
> > > >                    && ix86_cmodel != CM_LARGE_PIC)
> > > >             return true;
> > > >           break;
> > > > @@ -22892,10 +22888,7 @@ ix86_atomic_assign_expand_fenv (tree *hold,
> tree *clear, tree *update)
> > > >  static bool
> > > >  ix86_binds_local_p (const_tree exp)
> > > >  {
> > > > -  return default_binds_local_p_3 (exp, flag_shlib != 0, true, true,
> > > > -                                 (!flag_pic
> > > > -                                  || (TARGET_64BIT
> > > > -                                      && HAVE_LD_PIE_COPYRELOC !=
> 0)));
> > > > +  return default_binds_local_p_3 (exp, flag_shlib != 0, true, true,
> !flag_pic);
> > > >  }
> > > >  #endif
> > > >
> > > > diff --git a/gcc/configure b/gcc/configure
> > > > index f03fe888384..c500f5ca11e 100755
> > > > --- a/gcc/configure
> > > > +++ b/gcc/configure
> > > > @@ -29968,58 +29968,6 @@ fi
> > > >  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $gcc_cv_ld_pie" >&5
> > > >  $as_echo "$gcc_cv_ld_pie" >&6; }
> > > >
> > > > -{ $as_echo "$as_me:${as_lineno-$LINENO}: checking linker PIE
> support with copy reloc" >&5
> > > > -$as_echo_n "checking linker PIE support with copy reloc... " >&6; }
> > > > -gcc_cv_ld_pie_copyreloc=no
> > > > -if test $gcc_cv_ld_pie = yes ; then
> > > > -  if test $in_tree_ld = yes ; then
> > > > -    if test "$gcc_cv_gld_major_version" -eq 2 -a
> "$gcc_cv_gld_minor_version" -ge 25 -o "$gcc_cv_gld_major_version" -gt 2;
> then
> > > > -      gcc_cv_ld_pie_copyreloc=yes
> > > > -    fi
> > > > -  elif test x$gcc_cv_as != x -a x$gcc_cv_ld != x ; then
> > > > -    # Check if linker supports -pie option with copy reloc
> > > > -    case "$target" in
> > > > -    i?86-*-linux* | x86_64-*-linux*)
> > > > -      cat > conftest1.s <<EOF
> > > > -       .globl  a_glob
> > > > -       .data
> > > > -       .type   a_glob, @object
> > > > -       .size   a_glob, 4
> > > > -a_glob:
> > > > -       .long   2
> > > > -EOF
> > > > -      cat > conftest2.s <<EOF
> > > > -       .text
> > > > -       .globl  main
> > > > -       .type   main, @function
> > > > -main:
> > > > -       movl    %eax, a_glob(%rip)
> > > > -       .size   main, .-main
> > > > -       .globl  ptr
> > > > -       .section        .data.rel,"aw",@progbits
> > > > -       .type   ptr, @object
> > > > -ptr:
> > > > -       .quad   a_glob
> > > > -EOF
> > > > -      if $gcc_cv_as --64 -o conftest1.o conftest1.s > /dev/null
> 2>&1 \
> > > > -         && $gcc_cv_ld -shared -melf_x86_64 -o conftest1.so
> conftest1.o > /dev/null 2>&1 \
> > > > -         && $gcc_cv_as --64 -o conftest2.o conftest2.s > /dev/null
> 2>&1 \
> > > > -         && $gcc_cv_ld -pie -melf_x86_64 -o conftest conftest2.o
> conftest1.so > /dev/null 2>&1; then
> > > > -        gcc_cv_ld_pie_copyreloc=yes
> > > > -      fi
> > > > -      rm -f conftest conftest1.so conftest1.o conftest2.o
> conftest1.s conftest2.s
> > > > -      ;;
> > > > -    esac
> > > > -  fi
> > > > -fi
> > > > -
> > > > -cat >>confdefs.h <<_ACEOF
> > > > -#define HAVE_LD_PIE_COPYRELOC `if test x"$gcc_cv_ld_pie_copyreloc"
> = xyes; then echo 1; else echo 0; fi`
> > > > -_ACEOF
> > > > -
> > > > -{ $as_echo "$as_me:${as_lineno-$LINENO}: result:
> $gcc_cv_ld_pie_copyreloc" >&5
> > > > -$as_echo "$gcc_cv_ld_pie_copyreloc" >&6; }
> > > > -
> > > >  { $as_echo "$as_me:${as_lineno-$LINENO}: checking linker
> EH-compatible garbage collection of sections" >&5
> > > >  $as_echo_n "checking linker EH-compatible garbage collection of
> sections... " >&6; }
> > > >  gcc_cv_ld_eh_gc_sections=no
> > > > diff --git a/gcc/configure.ac b/gcc/configure.ac
> > > > index e9ba2af548a..d60b22c1708 100644
> > > > --- a/gcc/configure.ac
> > > > +++ b/gcc/configure.ac
> > > > @@ -5924,54 +5924,6 @@ if test x"$gcc_cv_ld_pie" = xyes; then
> > > >  fi
> > > >  AC_MSG_RESULT($gcc_cv_ld_pie)
> > > >
> > > > -AC_MSG_CHECKING(linker PIE support with copy reloc)
> > > > -gcc_cv_ld_pie_copyreloc=no
> > > > -if test $gcc_cv_ld_pie = yes ; then
> > > > -  if test $in_tree_ld = yes ; then
> > > > -    if test "$gcc_cv_gld_major_version" -eq 2 -a
> "$gcc_cv_gld_minor_version" -ge 25 -o "$gcc_cv_gld_major_version" -gt 2;
> then
> > > > -      gcc_cv_ld_pie_copyreloc=yes
> > > > -    fi
> > > > -  elif test x$gcc_cv_as != x -a x$gcc_cv_ld != x ; then
> > > > -    # Check if linker supports -pie option with copy reloc
> > > > -    case "$target" in
> > > > -    i?86-*-linux* | x86_64-*-linux*)
> > > > -      cat > conftest1.s <<EOF
> > > > -       .globl  a_glob
> > > > -       .data
> > > > -       .type   a_glob, @object
> > > > -       .size   a_glob, 4
> > > > -a_glob:
> > > > -       .long   2
> > > > -EOF
> > > > -      cat > conftest2.s <<EOF
> > > > -       .text
> > > > -       .globl  main
> > > > -       .type   main, @function
> > > > -main:
> > > > -       movl    %eax, a_glob(%rip)
> > > > -       .size   main, .-main
> > > > -       .globl  ptr
> > > > -       .section        .data.rel,"aw",@progbits
> > > > -       .type   ptr, @object
> > > > -ptr:
> > > > -       .quad   a_glob
> > > > -EOF
> > > > -      if $gcc_cv_as --64 -o conftest1.o conftest1.s > /dev/null
> 2>&1 \
> > > > -         && $gcc_cv_ld -shared -melf_x86_64 -o conftest1.so
> conftest1.o > /dev/null 2>&1 \
> > > > -         && $gcc_cv_as --64 -o conftest2.o conftest2.s > /dev/null
> 2>&1 \
> > > > -         && $gcc_cv_ld -pie -melf_x86_64 -o conftest conftest2.o
> conftest1.so > /dev/null 2>&1; then
> > > > -        gcc_cv_ld_pie_copyreloc=yes
> > > > -      fi
> > > > -      rm -f conftest conftest1.so conftest1.o conftest2.o
> conftest1.s conftest2.s
> > > > -      ;;
> > > > -    esac
> > > > -  fi
> > > > -fi
> > > > -AC_DEFINE_UNQUOTED(HAVE_LD_PIE_COPYRELOC,
> > > > -  [`if test x"$gcc_cv_ld_pie_copyreloc" = xyes; then echo 1; else
> echo 0; fi`],
> > > > -  [Define 0/1 if your linker supports -pie option with copy reloc.])
> > > > -AC_MSG_RESULT($gcc_cv_ld_pie_copyreloc)
> > > > -
> > > >  AC_MSG_CHECKING(linker EH-compatible garbage collection of sections)
> > > >  gcc_cv_ld_eh_gc_sections=no
> > > >  if test $in_tree_ld = yes ; then
> > > > diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
> > > > index 3a1d6536833..1c8019ea04c 100644
> > > > --- a/gcc/doc/sourcebuild.texi
> > > > +++ b/gcc/doc/sourcebuild.texi
> > > > @@ -2383,9 +2383,6 @@ Target supports FPU instructions.
> > > >  @item non_strict_align
> > > >  Target does not require strict alignment.
> > > >
> > > > -@item pie_copyreloc
> > > > -The x86-64 target linker supports PIE with copy reloc.
> > > > -
> > > >  @item rdrand
> > > >  Target supports x86 @code{rdrand} instruction.
> > > >
> > > > diff --git a/gcc/testsuite/gcc.target/i386/pie-copyrelocs-1.c
> b/gcc/testsuite/gcc.target/i386/pie-copyrelocs-1.c
> > > > deleted file mode 100644
> > > > index 7af851bde9b..00000000000
> > > > --- a/gcc/testsuite/gcc.target/i386/pie-copyrelocs-1.c
> > > > +++ /dev/null
> > > > @@ -1,14 +0,0 @@
> > > > -/* Check that GOTPCREL isn't used to access glob_a.  */
> > > > -/* { dg-do compile { target *-*-linux* } } */
> > > > -/* { dg-require-effective-target pie_copyreloc } */
> > > > -/* { dg-options "-O2 -fpie" } */
> > > > -
> > > > -extern int glob_a;
> > > > -
> > > > -int foo ()
> > > > -{
> > > > -  return glob_a;
> > > > -}
> > > > -
> > > > -/* glob_a should never be accessed with a GOTPCREL.  */
> > > > -/* { dg-final { scan-assembler-not "glob_a@GOTPCREL" { target { !
> ia32 } } } } */
> > > > diff --git a/gcc/testsuite/gcc.target/i386/pie-copyrelocs-2.c
> b/gcc/testsuite/gcc.target/i386/pie-copyrelocs-2.c
> > > > deleted file mode 100644
> > > > index 19cb97e882c..00000000000
> > > > --- a/gcc/testsuite/gcc.target/i386/pie-copyrelocs-2.c
> > > > +++ /dev/null
> > > > @@ -1,14 +0,0 @@
> > > > -/* Check that GOTPCREL isn't used to access glob_a.  */
> > > > -/* { dg-do compile { target *-*-linux* } } */
> > > > -/* { dg-require-effective-target pie_copyreloc } */
> > > > -/* { dg-options "-O2 -fpie" } */
> > > > -
> > > > -int glob_a;
> > > > -
> > > > -int foo ()
> > > > -{
> > > > -  return glob_a;
> > > > -}
> > > > -
> > > > -/* glob_a should never be accessed with a GOTPCREL.  */
> > > > -/* { dg-final { scan-assembler-not "glob_a@GOTPCREL" { target { !
> ia32 } } } } */
> > > > diff --git a/gcc/testsuite/gcc.target/i386/pie-copyrelocs-3.c
> b/gcc/testsuite/gcc.target/i386/pie-copyrelocs-3.c
> > > > deleted file mode 100644
> > > > index c2fa8968e77..00000000000
> > > > --- a/gcc/testsuite/gcc.target/i386/pie-copyrelocs-3.c
> > > > +++ /dev/null
> > > > @@ -1,14 +0,0 @@
> > > > -/* Check that PLT is used to access glob_a.  */
> > > > -/* { dg-do compile { target *-*-linux* } } */
> > > > -/* { dg-require-effective-target pie_copyreloc } */
> > > > -/* { dg-options "-O2 -fpie" } */
> > > > -
> > > > -extern int glob_a (void);
> > > > -
> > > > -int foo ()
> > > > -{
> > > > -  return glob_a ();
> > > > -}
> > > > -
> > > > -/* glob_a should be accessed with a PLT.  */
> > > > -/* { dg-final { scan-assembler "glob_a@PLT" { target { ! ia32 } }
> } } */
> > > > diff --git a/gcc/testsuite/gcc.target/i386/pie-copyrelocs-4.c
> b/gcc/testsuite/gcc.target/i386/pie-copyrelocs-4.c
> > > > deleted file mode 100644
> > > > index 413cdf381c3..00000000000
> > > > --- a/gcc/testsuite/gcc.target/i386/pie-copyrelocs-4.c
> > > > +++ /dev/null
> > > > @@ -1,17 +0,0 @@
> > > > -/* Check that GOTPCREL is used to access glob_a.  */
> > > > -/* { dg-do compile { target *-*-linux* } } */
> > > > -/* { dg-require-effective-target pie_copyreloc } */
> > > > -/* { dg-options "-O2 -fpie" } */
> > > > -
> > > > -extern int glob_a  __attribute__((weak));
> > > > -
> > > > -int foo ()
> > > > -{
> > > > -  if (&glob_a != 0)
> > > > -    return glob_a;
> > > > -  else
> > > > -    return 0;
> > > > -}
> > > > -
> > > > -/* weak glob_a should be accessed with a GOTPCREL.  */
> > > > -/* { dg-final { scan-assembler "glob_a@GOTPCREL" { target { ! ia32
> } } } } */
> > > > diff --git a/gcc/testsuite/lib/target-supports.exp
> b/gcc/testsuite/lib/target-supports.exp
> > > > index 5700c231065..6f922ebf2ab 100644
> > > > --- a/gcc/testsuite/lib/target-supports.exp
> > > > +++ b/gcc/testsuite/lib/target-supports.exp
> > > > @@ -10133,53 +10133,6 @@ proc
> scan-ltrans-tree-dump-dem-not_required_options {} {
> > > >      return "-flto-partition=one"
> > > >  }
> > > >
> > > > -# Return 1 if the x86-64 target supports PIE with copy reloc, 0
> > > > -# otherwise.  Cache the result.
> > > > -
> > > > -proc check_effective_target_pie_copyreloc { } {
> > > > -    global tool
> > > > -    global GCC_UNDER_TEST
> > > > -
> > > > -    if { !([istarget i?86-*-*] || [istarget x86_64-*-*]) } {
> > > > -       return 0
> > > > -    }
> > > > -
> > > > -    # Need auto-host.h to check linker support.
> > > > -    if { ![file exists ../../auto-host.h ] } {
> > > > -       return 0
> > > > -    }
> > > > -
> > > > -    return [check_cached_effective_target pie_copyreloc {
> > > > -       # Set up and compile to see if linker supports PIE with copy
> > > > -       # reloc.  Include the current process ID in the file names to
> > > > -       # prevent conflicts with invocations for multiple testsuites.
> > > > -
> > > > -       set src pie[pid].c
> > > > -       set obj pie[pid].o
> > > > -
> > > > -       set f [open $src "w"]
> > > > -       puts $f "#include \"../../auto-host.h\""
> > > > -       puts $f "#if HAVE_LD_PIE_COPYRELOC == 0"
> > > > -       puts $f "# error Linker does not support PIE with copy
> reloc."
> > > > -       puts $f "#endif"
> > > > -       close $f
> > > > -
> > > > -       verbose "check_effective_target_pie_copyreloc compiling
> testfile $src" 2
> > > > -       set lines [${tool}_target_compile $src $obj object ""]
> > > > -
> > > > -       file delete $src
> > > > -       file delete $obj
> > > > -
> > > > -       if [string match "" $lines] then {
> > > > -           verbose "check_effective_target_pie_copyreloc testfile
> compilation passed" 2
> > > > -           return 1
> > > > -       } else {
> > > > -           verbose "check_effective_target_pie_copyreloc testfile
> compilation failed" 2
> > > > -           return 0
> > > > -       }
> > > > -    }]
> > > > -}
> > > > -
> > > >  # Return 1 if the x86 target supports R_386_GOT32X relocation, 0
> > > >  # otherwise.  Cache the result.
> > > >
> > > > --
> > > > 2.31.1.607.g51e8a6a459-goog
> > > >
> > >
> > >
> > > --
> > > 宋方睿
> >
> >
> >
> > --
> > 宋方睿
>
>
>
> --
> 宋方睿
>


-- 
宋方睿