diff mbox series

[v6,1/5] elf: Support DT_RELR relative relocation format [BZ #27924]

Message ID 20220310200329.1935466-2-hjl.tools@gmail.com
State New
Headers show
Series Support DT_RELR relative relocation format | expand

Commit Message

H.J. Lu March 10, 2022, 8:03 p.m. UTC 
From: Fangrui Song <maskray@google.com>

PIE and shared objects usually have many relative relocations. In
2017/2018, SHT_RELR/DT_RELR was proposed on
https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
usually takes 3% or smaller space than R_*_RELATIVE relocations. The
virtual memory size of a mostly statically linked PIE is typically 5~10%
smaller.

---

Notes I will not include in the submitted commit:

Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr

"pre-standard": even Solaris folks are happy with the refined generic-abi
proposal. Cary Coutant will apply the change
https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html

This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
available to all ports. I don't think the current glibc implementation
supports ia64 in an ELFCLASS32 container. That said, the style I used is
works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
64-bit.

* Chrome OS folks have carried a local patch since 2018 (latest version:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
  I.e. this feature has been battle tested.
* Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
* The Linux kernel has supported CONFIG_RELR since 2019-08
  (https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
* A musl patch (by me) exists but is not applied:
  https://www.openwall.com/lists/musl/2019/03/06/3
* rtld-elf from FreeBSD 14 will support DT_RELR.

I believe upstream glibc should support DT_RELR to benefit all Linux
distributions. I filed some feature requests to get their attention:

* Gentoo: https://bugs.gentoo.org/818376
* Arch Linux: https://bugs.archlinux.org/task/72433
* Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
* Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699

As of linker support (to the best of my knowledge):

* LLD support DT_RELR.
* https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
  has a gold patch.
* GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923

Changes from the original patch:

1. Check the linker option, -z pack-relative-relocs, which add a
GLIBC_ABI_DT_RELR symbol version dependency on the shared C library if
it provides a GLIBC_2.XX symbol version.
2. Change make variale to have-dt-relr.
3. Rename tst-relr-no-pie to tst-relr-pie for --disable-default-pie.
4. Use TEST_VERIFY in tst-relr.c.
5. Add the check-tst-relr-pie.out test to check for linker generated
libc.so version dependency on GLIBC_ABI_DT_RELR.
6. Move ELF_DYNAMIC_DO_RELR before ELF_DYNAMIC_DO_REL.
---
 configure              | 42 +++++++++++++++++++++++++++
 configure.ac           | 10 +++++++
 elf/Makefile           | 14 +++++++++
 elf/dynamic-link.h     | 34 ++++++++++++++++++++++
 elf/elf.h              | 13 +++++++--
 elf/get-dynamic-info.h |  3 ++
 elf/tst-relr-pie.c     |  1 +
 elf/tst-relr.c         | 64 ++++++++++++++++++++++++++++++++++++++++++
 8 files changed, 179 insertions(+), 2 deletions(-)
 create mode 100644 elf/tst-relr-pie.c
 create mode 100644 elf/tst-relr.c

Comments

Adhemerval Zanella March 29, 2022, 4:34 p.m. UTC | #1 
On 10/03/2022 17:03, H.J. Lu via Libc-alpha wrote:
> From: Fangrui Song <maskray@google.com>
> 
> PIE and shared objects usually have many relative relocations. In
> 2017/2018, SHT_RELR/DT_RELR was proposed on
> https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
> ("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
> usually takes 3% or smaller space than R_*_RELATIVE relocations. The
> virtual memory size of a mostly statically linked PIE is typically 5~10%
> smaller.
> 
> ---
> 
> Notes I will not include in the submitted commit:
> 
> Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
> 
> "pre-standard": even Solaris folks are happy with the refined generic-abi
> proposal. Cary Coutant will apply the change
> https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
> 
> This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
> available to all ports. I don't think the current glibc implementation
> supports ia64 in an ELFCLASS32 container. That said, the style I used is
> works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
> 64-bit.

I really don't think ia64 ELFCLASS32 should be blocker for this change.

> 
> * Chrome OS folks have carried a local patch since 2018 (latest version:
>   https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
>   I.e. this feature has been battle tested.
> * Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
> * The Linux kernel has supported CONFIG_RELR since 2019-08
>   (https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
> * A musl patch (by me) exists but is not applied:
>   https://www.openwall.com/lists/musl/2019/03/06/3
> * rtld-elf from FreeBSD 14 will support DT_RELR.
> 
> I believe upstream glibc should support DT_RELR to benefit all Linux
> distributions. I filed some feature requests to get their attention:

Agreed.

> 
> * Gentoo: https://bugs.gentoo.org/818376
> * Arch Linux: https://bugs.archlinux.org/task/72433
> * Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
> * Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
> 
> As of linker support (to the best of my knowledge):
> 
> * LLD support DT_RELR.
> * https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
>   has a gold patch.
> * GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
> 
> Changes from the original patch:
> 
> 1. Check the linker option, -z pack-relative-relocs, which add a
> GLIBC_ABI_DT_RELR symbol version dependency on the shared C library if
> it provides a GLIBC_2.XX symbol version.
> 2. Change make variale to have-dt-relr.
> 3. Rename tst-relr-no-pie to tst-relr-pie for --disable-default-pie.
> 4. Use TEST_VERIFY in tst-relr.c.
> 5. Add the check-tst-relr-pie.out test to check for linker generated
> libc.so version dependency on GLIBC_ABI_DT_RELR.
> 6. Move ELF_DYNAMIC_DO_RELR before ELF_DYNAMIC_DO_REL.

Patch looks ok, some comments below.

> ---
>  configure              | 42 +++++++++++++++++++++++++++
>  configure.ac           | 10 +++++++
>  elf/Makefile           | 14 +++++++++
>  elf/dynamic-link.h     | 34 ++++++++++++++++++++++
>  elf/elf.h              | 13 +++++++--
>  elf/get-dynamic-info.h |  3 ++
>  elf/tst-relr-pie.c     |  1 +
>  elf/tst-relr.c         | 64 ++++++++++++++++++++++++++++++++++++++++++
>  8 files changed, 179 insertions(+), 2 deletions(-)
>  create mode 100644 elf/tst-relr-pie.c
>  create mode 100644 elf/tst-relr.c
> 
> diff --git a/configure b/configure
> index 8e5bee775a..9156e29fe9 100755
> --- a/configure
> +++ b/configure
> @@ -6115,6 +6115,48 @@ $as_echo "$libc_linker_feature" >&6; }
>  config_vars="$config_vars
>  have-depaudit = $libc_cv_depaudit"
>  
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z pack-relative-relocs" >&5
> +$as_echo_n "checking for linker that supports -z pack-relative-relocs... " >&6; }
> +libc_linker_feature=no
> +if test x"$gnu_ld" = x"yes"; then
> +  cat > conftest.c <<EOF
> +int _start (void) { return 42; }
> +EOF
> +  if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> +		    -Wl,-z,pack-relative-relocs -nostdlib -nostartfiles
> +		    -fPIC -shared -o conftest.so conftest.c
> +		    1>&5'
> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> +  (eval $ac_try) 2>&5
> +  ac_status=$?
> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> +  test $ac_status = 0; }; }
> +  then
> +    if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,pack-relative-relocs -nostdlib \
> +	-nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \
> +	| grep "warning: -z pack-relative-relocs ignored" > /dev/null 2>&1; then
> +      true
> +    else
> +      libc_linker_feature=yes
> +    fi
> +  fi
> +  rm -f conftest*
> +fi
> +if test $libc_linker_feature = yes; then
> +  libc_cv_dt_relr=yes
> +else
> +  libc_cv_dt_relr=no
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> +$as_echo "$libc_linker_feature" >&6; }
> +config_vars="$config_vars
> +have-dt-relr = $libc_cv_dt_relr"
> +if test "$libc_cv_dt_relr" = yes; then
> +  have_dt_relr=1
> +else
> +  have_dt_relr=0
> +fi
> +
>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
>  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
>  libc_linker_feature=no
> diff --git a/configure.ac b/configure.ac
> index 87f67d25ec..5c09871fee 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1367,6 +1367,16 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
>  		    [libc_cv_depaudit=yes], [libc_cv_depaudit=no])
>  LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
>  
> +LIBC_LINKER_FEATURE([-z pack-relative-relocs],
> +		    [-Wl,-z,pack-relative-relocs],
> +		    [libc_cv_dt_relr=yes], [libc_cv_dt_relr=no])
> +LIBC_CONFIG_VAR([have-dt-relr], [$libc_cv_dt_relr])

> +if test "$libc_cv_dt_relr" = yes; then
> +  have_dt_relr=1
> +else
> +  have_dt_relr=0
> +fi
> +

I think you don't need to setup have_dt_relr, it does not accomplish anything here
(LIBC_CONFIG_VAR already sets the required have-dt-relr on config.make).

>  LIBC_LINKER_FEATURE([--no-dynamic-linker],
>  		    [-Wl,--no-dynamic-linker],
>  		    [libc_cv_no_dynamic_linker=yes],
> diff --git a/elf/Makefile b/elf/Makefile
> index c96924e9c2..fd462ba315 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -541,6 +541,14 @@ tests-special += \
>    # tests-special
>  endif
>  endif
> +ifeq ($(have-dt-relr),yes)
> +tests += tst-relr tst-relr-pie
> +tests-pie += tst-relr-pie
> +tests-special += $(objpfx)check-tst-relr-pie.out

Please use one line per test:

 tests += \
   tst-relr \
   tst-relr-pie \
   # tests
 tests-pie +=
   tst-relr-pie \
   # tests-pie
 tests-special += \
   $(objpfx)check-tst-relr-pie.out \
   # tests-special

Also, the tst-rel-pie should only be added if $(have-fpie):

  ifeq ($(have-fpie),yes)
  tests-pie += \
    tst-relr-pie \
    #tests-pie
  endf

> +CFLAGS-tst-relr-pie.c += $(pie-ccflag)
> +LDFLAGS-tst-relr += -Wl,-z,pack-relative-relocs
> +LDFLAGS-tst-relr-pie += -Wl,-z,pack-relative-relocs
> +endif
>  endif
>  
>  ifeq ($(run-built-tests),yes)
> @@ -2725,3 +2733,9 @@ $(objpfx)tst-p_align3: $(objpfx)tst-p_alignmod3.so
>  $(objpfx)tst-p_align3.out: tst-p_align3.sh $(objpfx)tst-p_align3
>  	$(SHELL) $< $(common-objpfx) '$(test-program-prefix)'; \
>  	$(evaluate-test)
> +
> +$(objpfx)check-tst-relr-pie.out: $(objpfx)tst-relr-pie
> +	LC_ALL=C $(OBJDUMP) -p $< \
> +		| sed -ne '/required from libc.so/,$$ p' \
> +		| grep GLIBC_ABI_DT_RELR > $@; \
> +	$(evaluate-test)

Ok.

> diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
> index 25dd7ca4f2..d04c457e55 100644
> --- a/elf/dynamic-link.h
> +++ b/elf/dynamic-link.h
> @@ -146,12 +146,46 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
>  #  define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do.  */
>  # endif
>  
> +# define ELF_DYNAMIC_DO_RELR(map)					      \
> +  do {									      \
> +    ElfW(Addr) l_addr = (map)->l_addr, *where = 0;			      \
> +    const ElfW(Relr) *r, *end;						      \
> +    if (!(map)->l_info[DT_RELR])					      \
> +      break;								      \
> +    r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]);		      \
> +    end = (const ElfW(Relr) *)((const char *)r +			      \
> +                               (map)->l_info[DT_RELRSZ]->d_un.d_val);	      \
> +    for (; r < end; r++)						      \
> +      {									      \
> +	ElfW(Relr) entry = *r;						      \
> +	if ((entry & 1) == 0)						      \
> +	  {								      \
> +	    where = (ElfW(Addr) *)(l_addr + entry);			      \
> +	    *where++ += l_addr;						      \
> +	  }								      \
> +	else 								      \
> +	  {								      \
> +	    for (long i = 0; (entry >>= 1) != 0; i++)			      \
> +	      if ((entry & 1) != 0)					      \
> +		where[i] += l_addr;					      \
> +	    where += CHAR_BIT * sizeof(ElfW(Relr)) - 1;			      \
> +	  }								      \
> +      }									      \
> +  } while (0);
> +
>  /* This can't just be an inline function because GCC is too dumb
>     to inline functions containing inlines themselves.  */
> +# ifdef RTLD_BOOTSTRAP
> +#  define DO_RTLD_BOOTSTRAP 1
> +# else
> +#  define DO_RTLD_BOOTSTRAP 0
> +# endif
>  # define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
>    do {									      \
>      int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy),	      \
>  					      (consider_profile));	      \
> +    if (((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP))		      \
> +      ELF_DYNAMIC_DO_RELR (map);					      \
>      ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc);		      \
>      ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc);		      \
>    } while (0)

Ok.

> diff --git a/elf/elf.h b/elf/elf.h
> index 0735f6b579..0195029188 100644
> --- a/elf/elf.h
> +++ b/elf/elf.h
> @@ -443,7 +443,8 @@ typedef struct
>  #define SHT_PREINIT_ARRAY 16		/* Array of pre-constructors */
>  #define SHT_GROUP	  17		/* Section group */
>  #define SHT_SYMTAB_SHNDX  18		/* Extended section indices */
> -#define	SHT_NUM		  19		/* Number of defined types.  */
> +#define SHT_RELR	  19            /* RELR relative relocations */
> +#define	SHT_NUM		  20		/* Number of defined types.  */
>  #define SHT_LOOS	  0x60000000	/* Start OS-specific.  */
>  #define SHT_GNU_ATTRIBUTES 0x6ffffff5	/* Object attributes.  */
>  #define SHT_GNU_HASH	  0x6ffffff6	/* GNU-style hash table.  */
> @@ -662,6 +663,11 @@ typedef struct
>    Elf64_Sxword	r_addend;		/* Addend */
>  } Elf64_Rela;
>  

Ok.

> +/* RELR relocation table entry */
> +
> +typedef Elf32_Word	Elf32_Relr;
> +typedef Elf64_Xword	Elf64_Relr;
> +
>  /* How to extract and insert information held in the r_info field.  */
>  
>  #define ELF32_R_SYM(val)		((val) >> 8)
> @@ -887,7 +893,10 @@ typedef struct
>  #define DT_PREINIT_ARRAY 32		/* Array with addresses of preinit fct*/
>  #define DT_PREINIT_ARRAYSZ 33		/* size in bytes of DT_PREINIT_ARRAY */
>  #define DT_SYMTAB_SHNDX	34		/* Address of SYMTAB_SHNDX section */
> -#define	DT_NUM		35		/* Number used */
> +#define DT_RELRSZ	35		/* Total size of RELR relative relocations */
> +#define DT_RELR		36		/* Address of RELR relative relocations */
> +#define DT_RELRENT	37		/* Size of one RELR relative relocaction */
> +#define	DT_NUM		38		/* Number used */
>  #define DT_LOOS		0x6000000d	/* Start of OS-specific */
>  #define DT_HIOS		0x6ffff000	/* End of OS-specific */
>  #define DT_LOPROC	0x70000000	/* Start of processor-specific */

Ok.

> diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
> index 6c2ccd6db4..6c2a3a12b1 100644
> --- a/elf/get-dynamic-info.h
> +++ b/elf/get-dynamic-info.h
> @@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
>  # if ! ELF_MACHINE_NO_REL
>        ADJUST_DYN_INFO (DT_REL);
>  # endif
> +      ADJUST_DYN_INFO (DT_RELR);
>        ADJUST_DYN_INFO (DT_JMPREL);
>        ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
>        ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
> @@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
>    if (info[DT_REL] != NULL)
>      assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
>  #endif
> +  if (info[DT_RELR] != NULL)
> +    assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
>    if (bootstrap || static_pie_bootstrap)
>      {
>        assert (info[DT_RUNPATH] == NULL);

Ok.

> diff --git a/elf/tst-relr-pie.c b/elf/tst-relr-pie.c
> new file mode 100644
> index 0000000000..7df0cdbfd6
> --- /dev/null
> +++ b/elf/tst-relr-pie.c
> @@ -0,0 +1 @@
> +#include "tst-relr.c"
> diff --git a/elf/tst-relr.c b/elf/tst-relr.c

Ok.

> new file mode 100644
> index 0000000000..56addd2ad4
> --- /dev/null
> +++ b/elf/tst-relr.c
> @@ -0,0 +1,64 @@
> +/* Basic tests for DT_RELR.
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <link.h>
> +#include <stdbool.h>
> +#include <support/check.h>
> +
> +static int o, x;
> +
> +#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
> +#define E 0,
> +
> +#define O &o,
> +#define X &x,
> +void *arr[] = { ELEMS };
> +#undef O
> +#undef X
> +
> +#define O 1,
> +#define X 2,
> +static char val[] = { ELEMS };
> +
> +static int
> +do_test (void)
> +{
> +  ElfW(Dyn) *d = _DYNAMIC;
> +  if (d)
> +    {
> +      bool has_relr = false;
> +      for (; d->d_tag != DT_NULL; d++)
> +	if (d->d_tag == DT_RELR)
> +	  has_relr = true;
> +
> +#if defined __PIE__ || defined __pie__ || defined PIE || defined pie
> +      TEST_VERIFY (has_relr);
> +#else
> +      TEST_VERIFY (!has_relr);
> +#endif
> +    }
> +
> +  for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)

Use array_length here.

> +    TEST_VERIFY ((arr[i] == 0 && val[i] == 0)
> +		 || (arr[i] == &o && val[i] == 1)
> +		 || (arr[i] == &x && val[i] == 2));
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>

This fails without the rest of the patchset applied:

$ ./testrun.sh elf/tst-relr
elf/tst-relr: ./libc.so.6: version `GLIBC_ABI_DT_RELR' not found (required by elf/tst-relr)

I suggest you move it to third patch when GLIBC_ABI_DT_RELR is added.
H.J. Lu March 29, 2022, 10:34 p.m. UTC | #2 
On Tue, Mar 29, 2022 at 9:34 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 10/03/2022 17:03, H.J. Lu via Libc-alpha wrote:
> > From: Fangrui Song <maskray@google.com>
> >
> > PIE and shared objects usually have many relative relocations. In
> > 2017/2018, SHT_RELR/DT_RELR was proposed on
> > https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ
> > ("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR
> > usually takes 3% or smaller space than R_*_RELATIVE relocations. The
> > virtual memory size of a mostly statically linked PIE is typically 5~10%
> > smaller.
> >
> > ---
> >
> > Notes I will not include in the submitted commit:
> >
> > Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
> >
> > "pre-standard": even Solaris folks are happy with the refined generic-abi
> > proposal. Cary Coutant will apply the change
> > https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html
> >
> > This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR
> > available to all ports. I don't think the current glibc implementation
> > supports ia64 in an ELFCLASS32 container. That said, the style I used is
> > works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is
> > 64-bit.
>
> I really don't think ia64 ELFCLASS32 should be blocker for this change.
>
> >
> > * Chrome OS folks have carried a local patch since 2018 (latest version:
> >   https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32).
> >   I.e. this feature has been battle tested.
> > * Android bionic supports 2018 and switched to DT_RELR==36 in 2020.
> > * The Linux kernel has supported CONFIG_RELR since 2019-08
> >   (https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d).
> > * A musl patch (by me) exists but is not applied:
> >   https://www.openwall.com/lists/musl/2019/03/06/3
> > * rtld-elf from FreeBSD 14 will support DT_RELR.
> >
> > I believe upstream glibc should support DT_RELR to benefit all Linux
> > distributions. I filed some feature requests to get their attention:
>
> Agreed.
>
> >
> > * Gentoo: https://bugs.gentoo.org/818376
> > * Arch Linux: https://bugs.archlinux.org/task/72433
> > * Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598
> > * Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699
> >
> > As of linker support (to the best of my knowledge):
> >
> > * LLD support DT_RELR.
> > * https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/
> >   has a gold patch.
> > * GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923
> >
> > Changes from the original patch:
> >
> > 1. Check the linker option, -z pack-relative-relocs, which add a
> > GLIBC_ABI_DT_RELR symbol version dependency on the shared C library if
> > it provides a GLIBC_2.XX symbol version.
> > 2. Change make variale to have-dt-relr.
> > 3. Rename tst-relr-no-pie to tst-relr-pie for --disable-default-pie.
> > 4. Use TEST_VERIFY in tst-relr.c.
> > 5. Add the check-tst-relr-pie.out test to check for linker generated
> > libc.so version dependency on GLIBC_ABI_DT_RELR.
> > 6. Move ELF_DYNAMIC_DO_RELR before ELF_DYNAMIC_DO_REL.
>
> Patch looks ok, some comments below.
>
> > ---
> >  configure              | 42 +++++++++++++++++++++++++++
> >  configure.ac           | 10 +++++++
> >  elf/Makefile           | 14 +++++++++
> >  elf/dynamic-link.h     | 34 ++++++++++++++++++++++
> >  elf/elf.h              | 13 +++++++--
> >  elf/get-dynamic-info.h |  3 ++
> >  elf/tst-relr-pie.c     |  1 +
> >  elf/tst-relr.c         | 64 ++++++++++++++++++++++++++++++++++++++++++
> >  8 files changed, 179 insertions(+), 2 deletions(-)
> >  create mode 100644 elf/tst-relr-pie.c
> >  create mode 100644 elf/tst-relr.c
> >
> > diff --git a/configure b/configure
> > index 8e5bee775a..9156e29fe9 100755
> > --- a/configure
> > +++ b/configure
> > @@ -6115,6 +6115,48 @@ $as_echo "$libc_linker_feature" >&6; }
> >  config_vars="$config_vars
> >  have-depaudit = $libc_cv_depaudit"
> >
> > +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z pack-relative-relocs" >&5
> > +$as_echo_n "checking for linker that supports -z pack-relative-relocs... " >&6; }
> > +libc_linker_feature=no
> > +if test x"$gnu_ld" = x"yes"; then
> > +  cat > conftest.c <<EOF
> > +int _start (void) { return 42; }
> > +EOF
> > +  if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> > +                 -Wl,-z,pack-relative-relocs -nostdlib -nostartfiles
> > +                 -fPIC -shared -o conftest.so conftest.c
> > +                 1>&5'
> > +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> > +  (eval $ac_try) 2>&5
> > +  ac_status=$?
> > +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> > +  test $ac_status = 0; }; }
> > +  then
> > +    if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,pack-relative-relocs -nostdlib \
> > +     -nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \
> > +     | grep "warning: -z pack-relative-relocs ignored" > /dev/null 2>&1; then
> > +      true
> > +    else
> > +      libc_linker_feature=yes
> > +    fi
> > +  fi
> > +  rm -f conftest*
> > +fi
> > +if test $libc_linker_feature = yes; then
> > +  libc_cv_dt_relr=yes
> > +else
> > +  libc_cv_dt_relr=no
> > +fi
> > +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> > +$as_echo "$libc_linker_feature" >&6; }
> > +config_vars="$config_vars
> > +have-dt-relr = $libc_cv_dt_relr"
> > +if test "$libc_cv_dt_relr" = yes; then
> > +  have_dt_relr=1
> > +else
> > +  have_dt_relr=0
> > +fi
> > +
> >  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
> >  $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
> >  libc_linker_feature=no
> > diff --git a/configure.ac b/configure.ac
> > index 87f67d25ec..5c09871fee 100644
> > --- a/configure.ac
> > +++ b/configure.ac
> > @@ -1367,6 +1367,16 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
> >                   [libc_cv_depaudit=yes], [libc_cv_depaudit=no])
> >  LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
> >
> > +LIBC_LINKER_FEATURE([-z pack-relative-relocs],
> > +                 [-Wl,-z,pack-relative-relocs],
> > +                 [libc_cv_dt_relr=yes], [libc_cv_dt_relr=no])
> > +LIBC_CONFIG_VAR([have-dt-relr], [$libc_cv_dt_relr])
>
> > +if test "$libc_cv_dt_relr" = yes; then
> > +  have_dt_relr=1
> > +else
> > +  have_dt_relr=0
> > +fi
> > +
>
> I think you don't need to setup have_dt_relr, it does not accomplish anything here
> (LIBC_CONFIG_VAR already sets the required have-dt-relr on config.make).

Fixed in v7.

> >  LIBC_LINKER_FEATURE([--no-dynamic-linker],
> >                   [-Wl,--no-dynamic-linker],
> >                   [libc_cv_no_dynamic_linker=yes],
> > diff --git a/elf/Makefile b/elf/Makefile
> > index c96924e9c2..fd462ba315 100644
> > --- a/elf/Makefile
> > +++ b/elf/Makefile
> > @@ -541,6 +541,14 @@ tests-special += \
> >    # tests-special
> >  endif
> >  endif
> > +ifeq ($(have-dt-relr),yes)
> > +tests += tst-relr tst-relr-pie
> > +tests-pie += tst-relr-pie
> > +tests-special += $(objpfx)check-tst-relr-pie.out
>
> Please use one line per test:
>
>  tests += \
>    tst-relr \
>    tst-relr-pie \
>    # tests
>  tests-pie +=
>    tst-relr-pie \
>    # tests-pie
>  tests-special += \
>    $(objpfx)check-tst-relr-pie.out \
>    # tests-special
>
> Also, the tst-rel-pie should only be added if $(have-fpie):
>
>   ifeq ($(have-fpie),yes)
>   tests-pie += \
>     tst-relr-pie \
>     #tests-pie
>   endf

Fixed in v7.

> > +CFLAGS-tst-relr-pie.c += $(pie-ccflag)
> > +LDFLAGS-tst-relr += -Wl,-z,pack-relative-relocs
> > +LDFLAGS-tst-relr-pie += -Wl,-z,pack-relative-relocs
> > +endif
> >  endif
> >
> >  ifeq ($(run-built-tests),yes)
> > @@ -2725,3 +2733,9 @@ $(objpfx)tst-p_align3: $(objpfx)tst-p_alignmod3.so
> >  $(objpfx)tst-p_align3.out: tst-p_align3.sh $(objpfx)tst-p_align3
> >       $(SHELL) $< $(common-objpfx) '$(test-program-prefix)'; \
> >       $(evaluate-test)
> > +
> > +$(objpfx)check-tst-relr-pie.out: $(objpfx)tst-relr-pie
> > +     LC_ALL=C $(OBJDUMP) -p $< \
> > +             | sed -ne '/required from libc.so/,$$ p' \
> > +             | grep GLIBC_ABI_DT_RELR > $@; \
> > +     $(evaluate-test)
>
> Ok.
>
> > diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
> > index 25dd7ca4f2..d04c457e55 100644
> > --- a/elf/dynamic-link.h
> > +++ b/elf/dynamic-link.h
> > @@ -146,12 +146,46 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
> >  #  define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do.  */
> >  # endif
> >
> > +# define ELF_DYNAMIC_DO_RELR(map)                                          \
> > +  do {                                                                             \
> > +    ElfW(Addr) l_addr = (map)->l_addr, *where = 0;                         \
> > +    const ElfW(Relr) *r, *end;                                                     \
> > +    if (!(map)->l_info[DT_RELR])                                           \
> > +      break;                                                               \
> > +    r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]);                 \
> > +    end = (const ElfW(Relr) *)((const char *)r +                           \
> > +                               (map)->l_info[DT_RELRSZ]->d_un.d_val);              \
> > +    for (; r < end; r++)                                                   \
> > +      {                                                                            \
> > +     ElfW(Relr) entry = *r;                                                \
> > +     if ((entry & 1) == 0)                                                 \
> > +       {                                                                   \
> > +         where = (ElfW(Addr) *)(l_addr + entry);                           \
> > +         *where++ += l_addr;                                               \
> > +       }                                                                   \
> > +     else                                                                  \
> > +       {                                                                   \
> > +         for (long i = 0; (entry >>= 1) != 0; i++)                         \
> > +           if ((entry & 1) != 0)                                           \
> > +             where[i] += l_addr;                                           \
> > +         where += CHAR_BIT * sizeof(ElfW(Relr)) - 1;                       \
> > +       }                                                                   \
> > +      }                                                                            \
> > +  } while (0);
> > +
> >  /* This can't just be an inline function because GCC is too dumb
> >     to inline functions containing inlines themselves.  */
> > +# ifdef RTLD_BOOTSTRAP
> > +#  define DO_RTLD_BOOTSTRAP 1
> > +# else
> > +#  define DO_RTLD_BOOTSTRAP 0
> > +# endif
> >  # define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
> >    do {                                                                             \
> >      int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy),              \
> >                                             (consider_profile));            \
> > +    if (((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP))                  \
> > +      ELF_DYNAMIC_DO_RELR (map);                                           \
> >      ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc);                     \
> >      ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc);                    \
> >    } while (0)
>
> Ok.
>
> > diff --git a/elf/elf.h b/elf/elf.h
> > index 0735f6b579..0195029188 100644
> > --- a/elf/elf.h
> > +++ b/elf/elf.h
> > @@ -443,7 +443,8 @@ typedef struct
> >  #define SHT_PREINIT_ARRAY 16         /* Array of pre-constructors */
> >  #define SHT_GROUP      17            /* Section group */
> >  #define SHT_SYMTAB_SHNDX  18         /* Extended section indices */
> > -#define      SHT_NUM           19            /* Number of defined types.  */
> > +#define SHT_RELR       19            /* RELR relative relocations */
> > +#define      SHT_NUM           20            /* Number of defined types.  */
> >  #define SHT_LOOS       0x60000000    /* Start OS-specific.  */
> >  #define SHT_GNU_ATTRIBUTES 0x6ffffff5        /* Object attributes.  */
> >  #define SHT_GNU_HASH   0x6ffffff6    /* GNU-style hash table.  */
> > @@ -662,6 +663,11 @@ typedef struct
> >    Elf64_Sxword       r_addend;               /* Addend */
> >  } Elf64_Rela;
> >
>
> Ok.
>
> > +/* RELR relocation table entry */
> > +
> > +typedef Elf32_Word   Elf32_Relr;
> > +typedef Elf64_Xword  Elf64_Relr;
> > +
> >  /* How to extract and insert information held in the r_info field.  */
> >
> >  #define ELF32_R_SYM(val)             ((val) >> 8)
> > @@ -887,7 +893,10 @@ typedef struct
> >  #define DT_PREINIT_ARRAY 32          /* Array with addresses of preinit fct*/
> >  #define DT_PREINIT_ARRAYSZ 33                /* size in bytes of DT_PREINIT_ARRAY */
> >  #define DT_SYMTAB_SHNDX      34              /* Address of SYMTAB_SHNDX section */
> > -#define      DT_NUM          35              /* Number used */
> > +#define DT_RELRSZ    35              /* Total size of RELR relative relocations */
> > +#define DT_RELR              36              /* Address of RELR relative relocations */
> > +#define DT_RELRENT   37              /* Size of one RELR relative relocaction */
> > +#define      DT_NUM          38              /* Number used */
> >  #define DT_LOOS              0x6000000d      /* Start of OS-specific */
> >  #define DT_HIOS              0x6ffff000      /* End of OS-specific */
> >  #define DT_LOPROC    0x70000000      /* Start of processor-specific */
>
> Ok.
>
> > diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
> > index 6c2ccd6db4..6c2a3a12b1 100644
> > --- a/elf/get-dynamic-info.h
> > +++ b/elf/get-dynamic-info.h
> > @@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
> >  # if ! ELF_MACHINE_NO_REL
> >        ADJUST_DYN_INFO (DT_REL);
> >  # endif
> > +      ADJUST_DYN_INFO (DT_RELR);
> >        ADJUST_DYN_INFO (DT_JMPREL);
> >        ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
> >        ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
> > @@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
> >    if (info[DT_REL] != NULL)
> >      assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
> >  #endif
> > +  if (info[DT_RELR] != NULL)
> > +    assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
> >    if (bootstrap || static_pie_bootstrap)
> >      {
> >        assert (info[DT_RUNPATH] == NULL);
>
> Ok.
>
> > diff --git a/elf/tst-relr-pie.c b/elf/tst-relr-pie.c
> > new file mode 100644
> > index 0000000000..7df0cdbfd6
> > --- /dev/null
> > +++ b/elf/tst-relr-pie.c
> > @@ -0,0 +1 @@
> > +#include "tst-relr.c"
> > diff --git a/elf/tst-relr.c b/elf/tst-relr.c
>
> Ok.
>
> > new file mode 100644
> > index 0000000000..56addd2ad4
> > --- /dev/null
> > +++ b/elf/tst-relr.c
> > @@ -0,0 +1,64 @@
> > +/* Basic tests for DT_RELR.
> > +   Copyright (C) 2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#include <link.h>
> > +#include <stdbool.h>
> > +#include <support/check.h>
> > +
> > +static int o, x;
> > +
> > +#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
> > +#define E 0,
> > +
> > +#define O &o,
> > +#define X &x,
> > +void *arr[] = { ELEMS };
> > +#undef O
> > +#undef X
> > +
> > +#define O 1,
> > +#define X 2,
> > +static char val[] = { ELEMS };
> > +
> > +static int
> > +do_test (void)
> > +{
> > +  ElfW(Dyn) *d = _DYNAMIC;
> > +  if (d)
> > +    {
> > +      bool has_relr = false;
> > +      for (; d->d_tag != DT_NULL; d++)
> > +     if (d->d_tag == DT_RELR)
> > +       has_relr = true;
> > +
> > +#if defined __PIE__ || defined __pie__ || defined PIE || defined pie
> > +      TEST_VERIFY (has_relr);
> > +#else
> > +      TEST_VERIFY (!has_relr);
> > +#endif
> > +    }
> > +
> > +  for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
>
> Use array_length here.

Fixed in v7.

> > +    TEST_VERIFY ((arr[i] == 0 && val[i] == 0)
> > +              || (arr[i] == &o && val[i] == 1)
> > +              || (arr[i] == &x && val[i] == 2));
> > +
> > +  return 0;
> > +}
> > +
> > +#include <support/test-driver.c>
>
> This fails without the rest of the patchset applied:
>
> $ ./testrun.sh elf/tst-relr
> elf/tst-relr: ./libc.so.6: version `GLIBC_ABI_DT_RELR' not found (required by elf/tst-relr)
>
> I suggest you move it to third patch when GLIBC_ABI_DT_RELR is added.

Fixed in v7.

The first patch just defines DT_RELR related macros and types.   The
second patch adds GLIBC_ABI_DT_RELR.

Thanks.
diff mbox series

Patch

diff --git a/configure b/configure
index 8e5bee775a..9156e29fe9 100755
--- a/configure
+++ b/configure
@@ -6115,6 +6115,48 @@  $as_echo "$libc_linker_feature" >&6; }
 config_vars="$config_vars
 have-depaudit = $libc_cv_depaudit"
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z pack-relative-relocs" >&5
+$as_echo_n "checking for linker that supports -z pack-relative-relocs... " >&6; }
+libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+  cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+  if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+		    -Wl,-z,pack-relative-relocs -nostdlib -nostartfiles
+		    -fPIC -shared -o conftest.so conftest.c
+		    1>&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+  then
+    if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,pack-relative-relocs -nostdlib \
+	-nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \
+	| grep "warning: -z pack-relative-relocs ignored" > /dev/null 2>&1; then
+      true
+    else
+      libc_linker_feature=yes
+    fi
+  fi
+  rm -f conftest*
+fi
+if test $libc_linker_feature = yes; then
+  libc_cv_dt_relr=yes
+else
+  libc_cv_dt_relr=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-dt-relr = $libc_cv_dt_relr"
+if test "$libc_cv_dt_relr" = yes; then
+  have_dt_relr=1
+else
+  have_dt_relr=0
+fi
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
 $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
 libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 87f67d25ec..5c09871fee 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1367,6 +1367,16 @@  LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
 		    [libc_cv_depaudit=yes], [libc_cv_depaudit=no])
 LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
 
+LIBC_LINKER_FEATURE([-z pack-relative-relocs],
+		    [-Wl,-z,pack-relative-relocs],
+		    [libc_cv_dt_relr=yes], [libc_cv_dt_relr=no])
+LIBC_CONFIG_VAR([have-dt-relr], [$libc_cv_dt_relr])
+if test "$libc_cv_dt_relr" = yes; then
+  have_dt_relr=1
+else
+  have_dt_relr=0
+fi
+
 LIBC_LINKER_FEATURE([--no-dynamic-linker],
 		    [-Wl,--no-dynamic-linker],
 		    [libc_cv_no_dynamic_linker=yes],
diff --git a/elf/Makefile b/elf/Makefile
index c96924e9c2..fd462ba315 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -541,6 +541,14 @@  tests-special += \
   # tests-special
 endif
 endif
+ifeq ($(have-dt-relr),yes)
+tests += tst-relr tst-relr-pie
+tests-pie += tst-relr-pie
+tests-special += $(objpfx)check-tst-relr-pie.out
+CFLAGS-tst-relr-pie.c += $(pie-ccflag)
+LDFLAGS-tst-relr += -Wl,-z,pack-relative-relocs
+LDFLAGS-tst-relr-pie += -Wl,-z,pack-relative-relocs
+endif
 endif
 
 ifeq ($(run-built-tests),yes)
@@ -2725,3 +2733,9 @@  $(objpfx)tst-p_align3: $(objpfx)tst-p_alignmod3.so
 $(objpfx)tst-p_align3.out: tst-p_align3.sh $(objpfx)tst-p_align3
 	$(SHELL) $< $(common-objpfx) '$(test-program-prefix)'; \
 	$(evaluate-test)
+
+$(objpfx)check-tst-relr-pie.out: $(objpfx)tst-relr-pie
+	LC_ALL=C $(OBJDUMP) -p $< \
+		| sed -ne '/required from libc.so/,$$ p' \
+		| grep GLIBC_ABI_DT_RELR > $@; \
+	$(evaluate-test)
diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
index 25dd7ca4f2..d04c457e55 100644
--- a/elf/dynamic-link.h
+++ b/elf/dynamic-link.h
@@ -146,12 +146,46 @@  elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
 #  define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do.  */
 # endif
 
+# define ELF_DYNAMIC_DO_RELR(map)					      \
+  do {									      \
+    ElfW(Addr) l_addr = (map)->l_addr, *where = 0;			      \
+    const ElfW(Relr) *r, *end;						      \
+    if (!(map)->l_info[DT_RELR])					      \
+      break;								      \
+    r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]);		      \
+    end = (const ElfW(Relr) *)((const char *)r +			      \
+                               (map)->l_info[DT_RELRSZ]->d_un.d_val);	      \
+    for (; r < end; r++)						      \
+      {									      \
+	ElfW(Relr) entry = *r;						      \
+	if ((entry & 1) == 0)						      \
+	  {								      \
+	    where = (ElfW(Addr) *)(l_addr + entry);			      \
+	    *where++ += l_addr;						      \
+	  }								      \
+	else 								      \
+	  {								      \
+	    for (long i = 0; (entry >>= 1) != 0; i++)			      \
+	      if ((entry & 1) != 0)					      \
+		where[i] += l_addr;					      \
+	    where += CHAR_BIT * sizeof(ElfW(Relr)) - 1;			      \
+	  }								      \
+      }									      \
+  } while (0);
+
 /* This can't just be an inline function because GCC is too dumb
    to inline functions containing inlines themselves.  */
+# ifdef RTLD_BOOTSTRAP
+#  define DO_RTLD_BOOTSTRAP 1
+# else
+#  define DO_RTLD_BOOTSTRAP 0
+# endif
 # define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
   do {									      \
     int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy),	      \
 					      (consider_profile));	      \
+    if (((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP))		      \
+      ELF_DYNAMIC_DO_RELR (map);					      \
     ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc);		      \
     ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc);		      \
   } while (0)
diff --git a/elf/elf.h b/elf/elf.h
index 0735f6b579..0195029188 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -443,7 +443,8 @@  typedef struct
 #define SHT_PREINIT_ARRAY 16		/* Array of pre-constructors */
 #define SHT_GROUP	  17		/* Section group */
 #define SHT_SYMTAB_SHNDX  18		/* Extended section indices */
-#define	SHT_NUM		  19		/* Number of defined types.  */
+#define SHT_RELR	  19            /* RELR relative relocations */
+#define	SHT_NUM		  20		/* Number of defined types.  */
 #define SHT_LOOS	  0x60000000	/* Start OS-specific.  */
 #define SHT_GNU_ATTRIBUTES 0x6ffffff5	/* Object attributes.  */
 #define SHT_GNU_HASH	  0x6ffffff6	/* GNU-style hash table.  */
@@ -662,6 +663,11 @@  typedef struct
   Elf64_Sxword	r_addend;		/* Addend */
 } Elf64_Rela;
 
+/* RELR relocation table entry */
+
+typedef Elf32_Word	Elf32_Relr;
+typedef Elf64_Xword	Elf64_Relr;
+
 /* How to extract and insert information held in the r_info field.  */
 
 #define ELF32_R_SYM(val)		((val) >> 8)
@@ -887,7 +893,10 @@  typedef struct
 #define DT_PREINIT_ARRAY 32		/* Array with addresses of preinit fct*/
 #define DT_PREINIT_ARRAYSZ 33		/* size in bytes of DT_PREINIT_ARRAY */
 #define DT_SYMTAB_SHNDX	34		/* Address of SYMTAB_SHNDX section */
-#define	DT_NUM		35		/* Number used */
+#define DT_RELRSZ	35		/* Total size of RELR relative relocations */
+#define DT_RELR		36		/* Address of RELR relative relocations */
+#define DT_RELRENT	37		/* Size of one RELR relative relocaction */
+#define	DT_NUM		38		/* Number used */
 #define DT_LOOS		0x6000000d	/* Start of OS-specific */
 #define DT_HIOS		0x6ffff000	/* End of OS-specific */
 #define DT_LOPROC	0x70000000	/* Start of processor-specific */
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 6c2ccd6db4..6c2a3a12b1 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -89,6 +89,7 @@  elf_get_dynamic_info (struct link_map *l, bool bootstrap,
 # if ! ELF_MACHINE_NO_REL
       ADJUST_DYN_INFO (DT_REL);
 # endif
+      ADJUST_DYN_INFO (DT_RELR);
       ADJUST_DYN_INFO (DT_JMPREL);
       ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
       ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
@@ -113,6 +114,8 @@  elf_get_dynamic_info (struct link_map *l, bool bootstrap,
   if (info[DT_REL] != NULL)
     assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
 #endif
+  if (info[DT_RELR] != NULL)
+    assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
   if (bootstrap || static_pie_bootstrap)
     {
       assert (info[DT_RUNPATH] == NULL);
diff --git a/elf/tst-relr-pie.c b/elf/tst-relr-pie.c
new file mode 100644
index 0000000000..7df0cdbfd6
--- /dev/null
+++ b/elf/tst-relr-pie.c
@@ -0,0 +1 @@ 
+#include "tst-relr.c"
diff --git a/elf/tst-relr.c b/elf/tst-relr.c
new file mode 100644
index 0000000000..56addd2ad4
--- /dev/null
+++ b/elf/tst-relr.c
@@ -0,0 +1,64 @@ 
+/* Basic tests for DT_RELR.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <link.h>
+#include <stdbool.h>
+#include <support/check.h>
+
+static int o, x;
+
+#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E
+#define E 0,
+
+#define O &o,
+#define X &x,
+void *arr[] = { ELEMS };
+#undef O
+#undef X
+
+#define O 1,
+#define X 2,
+static char val[] = { ELEMS };
+
+static int
+do_test (void)
+{
+  ElfW(Dyn) *d = _DYNAMIC;
+  if (d)
+    {
+      bool has_relr = false;
+      for (; d->d_tag != DT_NULL; d++)
+	if (d->d_tag == DT_RELR)
+	  has_relr = true;
+
+#if defined __PIE__ || defined __pie__ || defined PIE || defined pie
+      TEST_VERIFY (has_relr);
+#else
+      TEST_VERIFY (!has_relr);
+#endif
+    }
+
+  for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+    TEST_VERIFY ((arr[i] == 0 && val[i] == 0)
+		 || (arr[i] == &o && val[i] == 1)
+		 || (arr[i] == &x && val[i] == 2));
+
+  return 0;
+}
+
+#include <support/test-driver.c>