[PATCH 10/10] ld: Add glibc dependency for DT_RELR
Fangrui Song
i@maskray.me
Sat Jan 8 08:19:29 GMT 2022
On 2022-01-07, H.J. Lu wrote:
>On Fri, Jan 7, 2022 at 8:43 PM Fangrui Song <i@maskray.me> wrote:
>>
>> 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.
>
>I chose libc.so instead of ld.so since shared libraries may
>not be linked against ld.so. The glibc change can be simple:
>
>https://patchwork.sourceware.org/project/glibc/patch/20211123223053.3334224-1-hjl.tools@gmail.com/
>
>Please replace GLIBC_ABI_VERSION_GEN2 with
>GLIBC_ABI_DT_RELR.
>
>or like
>
>https://gitlab.com/x86-glibc/glibc/-/commit/3bc53baa5304855b5105dabd7726b23d454605fb
>
>I can go either way.
OK... I picked the first way:
https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr
>
>
>
>> >+ 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
>> >
>
>
>
>--
>H.J.
More information about the Libc-alpha
mailing list