[v2,4/9] ld: Initial DT_RELR support
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Add a -z pack-relative-relocs option to enable DT_RELR and create a
relr.dyn section for DT_RELR. DT_RELR is implemented with the linker
relaxation infrastructure, but it doesn't require the --relax option
enabled. -z pack-relative-relocs implies -z combreloc. -z nocombreloc
implies -z nopack-relative-relocs.
-z pack-relative-relocs is chosen over the similar option in lld,
--pack-dyn-relocs=relr, to implement a glibc binary lockout mechanism
with a special glibc version symbol, to avoid random crashes of DT_RELR
binaries with the existing glibc binaries.
bfd/
* elf-bfd.h (elf_link_hash_table): Add srelrdyn.
* elflink.c (_bfd_elf_link_create_dynamic_sections): Create a
.relr.dyn section for DT_RELR.
include/
* bfdlink.h (bfd_link_info): Add enable_dt_relr.
ld/
* News: Mention -z pack-relative-relocs and
-z nopack-relative-relocs.
* ld.texi: Document -z pack-relative-relocs and
-z nopack-relative-relocs.
* ldelf.c (ldelf_after_parse): Disable DT_RELR if not building
PIE nor shared library. Add 3 spare dynamic tags for DT_RELR,
DT_RELRSZ and DT_RELRENT.
* ldlang.c (lang_relax_sections): Also enable relaxation if
DT_RELR is enabled.
* emulparams/elf32_x86_64.sh: Source dt-relr.sh.
* emulparams/elf_i386.sh: Likewise.
* emulparams/elf_x86_64.sh: Likewise.
* emulparams/dt-relr.sh: New file.
* emultempl/elf.em (gld${EMULATION_NAME}_handle_option): Disable
DT_RELR for -z nocombreloc.
* scripttempl/elf.sc: Support .relr.dyn.
---
bfd/elf-bfd.h | 1 +
bfd/elflink.c | 11 +++++++++++
include/bfdlink.h | 4 ++++
ld/NEWS | 3 +++
ld/emulparams/dt-relr.sh | 21 +++++++++++++++++++++
ld/emulparams/elf32_x86_64.sh | 1 +
ld/emulparams/elf_i386.sh | 1 +
ld/emulparams/elf_x86_64.sh | 1 +
ld/emultempl/elf.em | 5 ++++-
ld/ld.texi | 11 +++++++++++
ld/ldelf.c | 9 +++++++++
ld/ldlang.c | 3 ++-
ld/scripttempl/elf.sc | 4 ++++
13 files changed, 73 insertions(+), 2 deletions(-)
create mode 100644 ld/emulparams/dt-relr.sh
@@ -707,6 +707,7 @@ struct elf_link_hash_table
asection *irelplt;
asection *irelifunc;
asection *dynsym;
+ asection *srelrdyn;
};
/* Returns TRUE if the hash table is a struct elf_link_hash_table. */
@@ -359,6 +359,17 @@ _bfd_elf_link_create_dynamic_sections (bfd *abfd, struct bfd_link_info *info)
elf_section_data (s)->this_hdr.sh_entsize = 4;
}
+ if (info->enable_dt_relr)
+ {
+ s = bfd_make_section_anyway_with_flags (abfd, ".relr.dyn",
+ (bed->dynamic_sec_flags
+ | SEC_READONLY));
+ if (s == NULL
+ || !bfd_set_section_alignment (s, bed->s->log_file_align))
+ return false;
+ elf_hash_table (info)->srelrdyn = s;
+ }
+
/* Let the backend create the rest of the sections. This lets the
backend set the right flags. The backend will normally create
the .got and .plt sections. */
@@ -413,6 +413,10 @@ struct bfd_link_info
/* TRUE if PT_GNU_RELRO segment should be created. */
unsigned int relro: 1;
+ /* TRUE if DT_RELR should be enabled for compact relative
+ relocations. */
+ unsigned int enable_dt_relr: 1;
+
/* TRUE if separate code segment should be created. */
unsigned int separate_code: 1;
@@ -1,5 +1,8 @@
-*- text -*-
+* Add -z pack-relative-relocs/-z no pack-relative-relocs to x86 ELF
+ linker to pack relative relocations in the DT_RELR section.
+
* Add support for the LoongArch architecture.
* Add -z indirect-extern-access/-z noindirect-extern-access to x86 ELF
new file mode 100644
@@ -0,0 +1,21 @@
+HAVE_DT_RELR=yes
+PARSE_AND_LIST_OPTIONS_PACK_RELATIVE_RELOCS='
+ fprintf (file, _("\
+ -z pack-relative-relocs Pack relative relocations\n"));
+ fprintf (file, _("\
+ -z nopack-relative-relocs Do not pack relative relocations (default)\n"));
+'
+
+PARSE_AND_LIST_ARGS_CASE_Z_PACK_RELATIVE_RELOCS='
+ else if (strcmp (optarg, "pack-relative-relocs") == 0)
+ {
+ link_info.enable_dt_relr = true;
+ link_info.combreloc = true;
+ }
+ else if (strcmp (optarg, "nopack-relative-relocs") == 0)
+ link_info.enable_dt_relr = false;
+'
+
+
+PARSE_AND_LIST_OPTIONS="$PARSE_AND_LIST_OPTIONS $PARSE_AND_LIST_OPTIONS_PACK_RELATIVE_RELOCS"
+PARSE_AND_LIST_ARGS_CASE_Z="$PARSE_AND_LIST_ARGS_CASE_Z $PARSE_AND_LIST_ARGS_CASE_Z_PACK_RELATIVE_RELOCS"
@@ -7,6 +7,7 @@ source_sh ${srcdir}/emulparams/cet.sh
source_sh ${srcdir}/emulparams/x86-report-relative.sh
source_sh ${srcdir}/emulparams/x86-64-level.sh
source_sh ${srcdir}/emulparams/static.sh
+source_sh ${srcdir}/emulparams/dt-relr.sh
SCRIPT_NAME=elf
ELFSIZE=32
OUTPUT_FORMAT="elf32-x86-64"
@@ -6,6 +6,7 @@ source_sh ${srcdir}/emulparams/cet.sh
source_sh ${srcdir}/emulparams/x86-report-relative.sh
source_sh ${srcdir}/emulparams/x86-64-level.sh
source_sh ${srcdir}/emulparams/static.sh
+source_sh ${srcdir}/emulparams/dt-relr.sh
SCRIPT_NAME=elf
OUTPUT_FORMAT="elf32-i386"
NO_RELA_RELOCS=yes
@@ -8,6 +8,7 @@ source_sh ${srcdir}/emulparams/x86-report-relative.sh
source_sh ${srcdir}/emulparams/x86-64-level.sh
source_sh ${srcdir}/emulparams/x86-64-lam.sh
source_sh ${srcdir}/emulparams/static.sh
+source_sh ${srcdir}/emulparams/dt-relr.sh
SCRIPT_NAME=elf
ELFSIZE=64
OUTPUT_FORMAT="elf64-x86-64"
@@ -822,7 +822,10 @@ fragment <<EOF
else if (strcmp (optarg, "combreloc") == 0)
link_info.combreloc = true;
else if (strcmp (optarg, "nocombreloc") == 0)
- link_info.combreloc = false;
+ {
+ link_info.combreloc = false;
+ link_info.enable_dt_relr = false;
+ }
else if (strcmp (optarg, "nocopyreloc") == 0)
link_info.nocopyreloc = true;
EOF
@@ -1242,6 +1242,7 @@ Supported for Linux/i386 and Linux/x86_64.
@itemx nocombreloc
Combine multiple dynamic relocation sections and sort to improve
dynamic symbol lookup caching. Do not do this if @samp{nocombreloc}.
+@samp{nocombreloc} implies @samp{nopack-relative-relocs}.
@item common
@itemx nocommon
@@ -1430,6 +1431,16 @@ called.
@item origin
Specify that the object requires @samp{$ORIGIN} handling in paths.
+@item pack-relative-relocs
+@itemx nopack-relative-relocs
+Generate compact relative relocation in position-independent executable
+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. This
+option also implies @option{combreloc}. @option{nopack-relative-relocs}
+is the default, which disables compact relative relocation. Supported
+for i386 and x86-64.
+
@item relro
@itemx norelro
Create an ELF @code{PT_GNU_RELRO} segment header in the object. This
@@ -71,6 +71,15 @@ ldelf_after_parse (void)
einfo (_("%P: warning: -z dynamic-undefined-weak ignored\n"));
link_info.dynamic_undefined_weak = 0;
}
+
+ /* Disable DT_RELR if not building PIE nor shared library. */
+ if (!bfd_link_pic (&link_info))
+ link_info.enable_dt_relr = 0;
+
+ /* Add 3 spare tags for DT_RELR, DT_RELRSZ and DT_RELRENT. */
+ if (link_info.enable_dt_relr)
+ link_info.spare_dynamic_tags += 3;
+
after_parse_default ();
if (link_info.commonpagesize > link_info.maxpagesize)
einfo (_("%F%P: common page size (0x%v) > maximum page size (0x%v)\n"),
@@ -7699,7 +7699,8 @@ lang_find_relro_sections (void)
void
lang_relax_sections (bool need_layout)
{
- if (RELAXATION_ENABLED)
+ /* NB: Also enable relaxation to layout sections for DT_RELR. */
+ if (RELAXATION_ENABLED || link_info.enable_dt_relr)
{
/* We may need more than one relaxation pass. */
int i = link_info.relax_pass;
@@ -10,6 +10,7 @@
# empty.
# HAVE_NOINIT - Include a .noinit output section in the script.
# HAVE_PERSISTENT - Include a .persistent output section in the script.
+# HAVE_DT_RELR - Include a .relr.dyn output section in the script.
# SMALL_DATA_CTOR - .ctors contains small data.
# SMALL_DATA_DTOR - .dtors contains small data.
# DATA_ADDR - if end-of-text-plus-one-page isn't right for data start
@@ -520,6 +521,9 @@ emit_dyn()
fi
fi
rm -f ldscripts/dyntmp.$$
+ if test -n "${COMBRELOC}" && test -n "${HAVE_DT_RELR}"; then
+ echo " .relr.dyn : { *(.relr.dyn) }"
+ fi
}
test -n "${NON_ALLOC_DYN}${SEPARATE_CODE}" || emit_dyn