[v5,1/5] elf: Support DT_RELR relative relocation format [BZ #27924]
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Commit Message
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.
---
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
On 2022-03-02, H.J. Lu 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.
>
>* 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.
>---
> 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
>+
> 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..5318079bac 100644
>--- a/elf/dynamic-link.h
>+++ b/elf/dynamic-link.h
>@@ -146,14 +146,48 @@ 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)); \
> ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
> ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
>+ if (((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP)) \
>+ ELF_DYNAMIC_DO_RELR (map); \
> } while (0)
>
> #endif
As mentioned on a binutils thread, ELF_DYNAMIC_DO_RELR needs to be
reordered before DL_REL/DO_RELA to help powerpc get the support in the future
https://sourceware.org/git/?p=glibc.git;a=blobdiff;f=elf/dynamic-link.h;h=169745f9a409aec7995f7418736ae64bfeebc9d6;hp=25dd7ca4f2eca3c97fdd1649c15e1b5106e70dc1;hb=1c6cc29baf9a4c7129ab2e94b0d4022bfa4f3299;hpb=edc696a73a7cb07b1aa68792a845a98d036ee7eb
>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>
>--
>2.35.1
>
On Thu, Mar 10, 2022 at 10:48 AM Fangrui Song <maskray@google.com> wrote:
>
>
> On 2022-03-02, H.J. Lu 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.
> >
> >* 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.
> >---
> > 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
> >+
> > 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..5318079bac 100644
> >--- a/elf/dynamic-link.h
> >+++ b/elf/dynamic-link.h
> >@@ -146,14 +146,48 @@ 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)); \
> > ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
> > ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
> >+ if (((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP)) \
> >+ ELF_DYNAMIC_DO_RELR (map); \
> > } while (0)
> >
> > #endif
>
> As mentioned on a binutils thread, ELF_DYNAMIC_DO_RELR needs to be
> reordered before DL_REL/DO_RELA to help powerpc get the support in the future
> https://sourceware.org/git/?p=glibc.git;a=blobdiff;f=elf/dynamic-link.h;h=169745f9a409aec7995f7418736ae64bfeebc9d6;hp=25dd7ca4f2eca3c97fdd1649c15e1b5106e70dc1;hb=1c6cc29baf9a4c7129ab2e94b0d4022bfa4f3299;hpb=edc696a73a7cb07b1aa68792a845a98d036ee7eb
Fixed in the v6 patch.
Thanks.
@@ -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
$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
libc_linker_feature=no
@@ -1367,6 +1367,16 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
LIBC_CONFIG_VAR([have-depaudit], [$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],
@@ -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)
@@ -146,14 +146,48 @@ 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)); \
ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
+ if (((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP)) \
+ ELF_DYNAMIC_DO_RELR (map); \
} while (0)
#endif
@@ -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 */
@@ -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);
new file mode 100644
@@ -0,0 +1 @@
+#include "tst-relr.c"
new file mode 100644
@@ -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>