ld: Add glibc dependency for DT_RELR

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.

5 files changed, 69 insertions, 1 deletions

diff --git a/ld/ld.texi b/ld/ld.texi
index 1b42c6b..fc75e9b 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -1437,7 +1437,9 @@ and shared library.  It adds @code{DT_RELR}, @code{DT_RELRSZ} and
 @code{DT_RELRENT} entries to the dynamic section.  It is ignored when
 building position-dependent executable and relocatable output.
 @option{nopack-relative-relocs} is the default, which disables compact
-relative relocation.  Supported for i386 and x86-64.
+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 0000000..beacffe
--- /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 0000000..51bda5d
--- /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 0000000..6556a6d
--- /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 0000000..51d21e4
--- /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" \
+    ] \
+]