[PATCH 10/10] ld: Add glibc dependency for DT_RELR
Fangrui Song
i@maskray.me
Sat Jan 8 04:43:09 GMT 2022
On 2022-01-07, H.J. Lu via Binutils wrote:
>When DT_RELR is enabled, to avoid random run-time crash with older glibc
>binaries without DT_RELR support, add a GLIBC_ABI_DT_RELR symbol version,
>which is provided by glibc with DT_RELR support, dependency on the shared
>C library if it provides a GLIBC_2.XX symbol version.
>
>bfd/
>
> * elflink.c (elf_link_add_dt_relr_dependency): New function.
> (bfd_elf_size_dynamic_sections): Call
> elf_link_add_dt_relr_dependency if DT_RELR is enabled.
>
>ld/
>
> * ld.texi: Mention GLIBC_ABI_DT_RELR in -z pack-relative-relocs
> entry.
> * testsuite/ld-elf/dt-relr-glibc-1.c: New file.
> * testsuite/ld-elf/dt-relr-glibc-1a.rd: Likewise.
> * testsuite/ld-elf/dt-relr-glibc-1b.rd: Likewise.
> * testsuite/ld-elf/dt-relr.exp: Likewise.
>---
> bfd/elflink.c | 86 +++++++++++++++++++++++++
> ld/ld.texi | 4 +-
> ld/testsuite/ld-elf/dt-relr-glibc-1.c | 11 ++++
> ld/testsuite/ld-elf/dt-relr-glibc-1a.rd | 4 ++
> ld/testsuite/ld-elf/dt-relr-glibc-1b.rd | 7 ++
> ld/testsuite/ld-elf/dt-relr.exp | 44 +++++++++++++
> 6 files changed, 155 insertions(+), 1 deletion(-)
> create mode 100644 ld/testsuite/ld-elf/dt-relr-glibc-1.c
> create mode 100644 ld/testsuite/ld-elf/dt-relr-glibc-1a.rd
> create mode 100644 ld/testsuite/ld-elf/dt-relr-glibc-1b.rd
> create mode 100644 ld/testsuite/ld-elf/dt-relr.exp
>
>diff --git a/bfd/elflink.c b/bfd/elflink.c
>index 31b13f5df7a..05ac1cb7a63 100644
>--- a/bfd/elflink.c
>+++ b/bfd/elflink.c
>@@ -2213,6 +2213,85 @@ _bfd_elf_export_symbol (struct elf_link_hash_entry *h, void *data)
> return true;
> }
>
>+/* Return true if GLIBC_ABI_DT_RELR is added to the list of version
>+ dependencies successfully. GLIBC_ABI_DT_RELR will be put into the
>+ .gnu.version_r section. */
>+
>+static bool
>+elf_link_add_dt_relr_dependency (struct elf_find_verdep_info *rinfo)
>+{
>+ bfd *glibc_bfd = NULL;
>+ Elf_Internal_Verneed *t;
>+ Elf_Internal_Vernaux *a;
>+ size_t amt;
>+ const char *relr = "GLIBC_ABI_DT_RELR";
>+
>+ /* See if we already know about GLIBC_PRIVATE_DT_RELR. */
>+ for (t = elf_tdata (rinfo->info->output_bfd)->verref;
>+ t != NULL;
>+ t = t->vn_nextref)
>+ {
>+ const char *soname = bfd_elf_get_dt_soname (t->vn_bfd);
>+ /* Skip the shared library if it isn't libc.so. */
>+ if (!soname || !startswith (soname, "libc.so."))
>+ continue;
Having the dependency on ld.so is better.
(The linker knows the --dynamic-linker value.)
libc.so does not need to know whether DT_RELR is used.
It's also easier on glibc side.
Defining __glibc_abi_dt_relr@@GLIBC_ABI_DT_RELR in elf/Versions is
simpler than defining it in libc.so and updating every libc.abilist.
>+ for (a = t->vn_auxptr; a != NULL; a = a->vna_nextptr)
>+ {
>+ /* Return if GLIBC_PRIVATE_DT_RELR dependency has been
>+ added. */
>+ if (a->vna_nodename == relr
>+ || strcmp (a->vna_nodename, relr) == 0)
>+ return true;
>+
>+ /* Check if libc.so provides GLIBC_2.XX version. */
>+ if (!glibc_bfd && startswith (a->vna_nodename, "GLIBC_2."))
>+ glibc_bfd = t->vn_bfd;
>+ }
>+
>+ break;
>+ }
>+
>+ /* Skip if it isn't linked against glibc. */
>+ if (glibc_bfd == NULL)
>+ return true;
>+
>+ /* This is a new version. Add it to tree we are building. */
>+ if (t == NULL)
>+ {
>+ amt = sizeof *t;
>+ t = (Elf_Internal_Verneed *) bfd_zalloc (rinfo->info->output_bfd,
>+ amt);
>+ if (t == NULL)
>+ {
>+ rinfo->failed = true;
>+ return false;
>+ }
>+
>+ t->vn_bfd = glibc_bfd;
>+ t->vn_nextref = elf_tdata (rinfo->info->output_bfd)->verref;
>+ elf_tdata (rinfo->info->output_bfd)->verref = t;
>+ }
>+
>+ amt = sizeof *a;
>+ a = (Elf_Internal_Vernaux *) bfd_zalloc (rinfo->info->output_bfd, amt);
>+ if (a == NULL)
>+ {
>+ rinfo->failed = true;
>+ return false;
>+ }
>+
>+ a->vna_nodename = relr;
>+ a->vna_flags = 0;
>+ a->vna_nextptr = t->vn_auxptr;
>+ a->vna_other = rinfo->vers + 1;
>+ ++rinfo->vers;
>+
>+ t->vn_auxptr = a;
>+
>+ return true;
>+}
>+
> /* Look through the symbols which are defined in other shared
> libraries and referenced here. Update the list of version
> dependencies. This will be put into the .gnu.version_r section.
>@@ -6940,6 +7019,13 @@ bfd_elf_size_dynamic_sections (bfd *output_bfd,
> if (sinfo.failed)
> return false;
>
>+ if (info->enable_dt_relr)
>+ {
>+ elf_link_add_dt_relr_dependency (&sinfo);
>+ if (sinfo.failed)
>+ return false;
>+ }
>+
> if (elf_tdata (output_bfd)->verref == NULL)
> s->flags |= SEC_EXCLUDE;
> else
>diff --git a/ld/ld.texi b/ld/ld.texi
>index 457089ec06a..a16657ddb45 100644
>--- a/ld/ld.texi
>+++ b/ld/ld.texi
>@@ -1439,7 +1439,9 @@ and shared library. It adds @code{DT_RELR}, @code{DT_RELRSZ} and
> building position-dependent executable and relocatable output. This
> option also implies @option{combreloc} and @option{--relax}.
> @option{nopack-relative-relocs} is the default, which disables
>-compact relative relocation. Supported for i386 and x86-64.
>+compact relative relocation. When linked against the GNU C Library,
>+a GLIBC_ABI_DT_RELR symbol version dependency on the shared C Library
>+is added to the output. Supported for i386 and x86-64.
> @item relro
> @itemx norelro
>diff --git a/ld/testsuite/ld-elf/dt-relr-glibc-1.c b/ld/testsuite/ld-elf/dt-relr-glibc-1.c
>new file mode 100644
>index 00000000000..beacffe29e7
>--- /dev/null
>+++ b/ld/testsuite/ld-elf/dt-relr-glibc-1.c
>@@ -0,0 +1,11 @@
>+#define REL(n) \
>+ static int data##n; \
>+ void *p##n = &data##n;
>+
>+REL(1)
>+REL(2)
>+REL(3)
>+REL(4)
>+REL(5)
>+REL(6)
>+REL(7)
>diff --git a/ld/testsuite/ld-elf/dt-relr-glibc-1a.rd b/ld/testsuite/ld-elf/dt-relr-glibc-1a.rd
>new file mode 100644
>index 00000000000..51bda5d70a1
>--- /dev/null
>+++ b/ld/testsuite/ld-elf/dt-relr-glibc-1a.rd
>@@ -0,0 +1,4 @@
>+#failif
>+#...
>+ 0x[a-f0-9]+: Name: GLIBC_ABI_DT_RELR Flags: none Version: [0-9]+
>+#...
>diff --git a/ld/testsuite/ld-elf/dt-relr-glibc-1b.rd b/ld/testsuite/ld-elf/dt-relr-glibc-1b.rd
>new file mode 100644
>index 00000000000..6556a6d939e
>--- /dev/null
>+++ b/ld/testsuite/ld-elf/dt-relr-glibc-1b.rd
>@@ -0,0 +1,7 @@
>+#...
>+Version needs section '.gnu.version_r' contains 1 entry:
>+ Addr: 0x[0-9a-f]+ +Offset: 0x[0-9a-f]+ +Link: +[0-9]+ +\(.dynstr\)
>+ +0+: Version: 1 +File: libc\.so\.6(|\.1) +Cnt: +[0-9]+
>+#...
>+ 0x[a-f0-9]+: Name: GLIBC_ABI_DT_RELR Flags: none Version: [0-9]+
>+#pass
>diff --git a/ld/testsuite/ld-elf/dt-relr.exp b/ld/testsuite/ld-elf/dt-relr.exp
>new file mode 100644
>index 00000000000..51d21e400ab
>--- /dev/null
>+++ b/ld/testsuite/ld-elf/dt-relr.exp
>@@ -0,0 +1,44 @@
>+# Expect script for DT_RELR.
>+# Copyright (C) 2022 Free Software Foundation, Inc.
>+#
>+# This file is part of the GNU Binutils.
>+#
>+# This program is free software; you can redistribute it and/or modify
>+# it under the terms of the GNU General Public License as published by
>+# the Free Software Foundation; either version 3 of the License, or
>+# (at your option) any later version.
>+#
>+# This program 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 General Public License for more details.
>+#
>+# You should have received a copy of the GNU General Public License
>+# along with this program; if not, write to the Free Software
>+# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
>+# MA 02110-1301, USA.
>+#
>+
>+# Linux tests.
>+if { ![istarget "*-*-linux*"] } {
>+ return
>+}
>+
>+run_cc_link_tests [list \
>+ [list \
>+ "Build dt-relr-glibc-1a.so" \
>+ "-shared $NO_DT_RELR_CC_LDFLAGS" \
>+ "-fPIC" \
>+ { dt-relr-glibc-1.c } \
>+ {{readelf {--version-info} dt-relr-glibc-1a.rd}} \
>+ "glibc-relr-1a.so" \
>+ ] \
>+ [list \
>+ "Build dt-relr-glibc-1b.so" \
>+ "-shared $DT_RELR_CC_LDFLAGS" \
>+ "-fPIC" \
>+ { dt-relr-glibc-1.c } \
>+ {{readelf {-W --version-info} dt-relr-glibc-1b.rd}} \
>+ "dt-relr-glibc-1b.so" \
>+ ] \
>+]
>--
>2.33.1
>
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