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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.
	* scripttempl/elf.sc: Support .relr.dyn.
This commit is contained in:
H.J. Lu
2022-01-03 06:50:20 -08:00
parent e2cbf4df83
commit 6a91be8666
12 changed files with 64 additions and 1 deletions
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4
ld/scripttempl/elf.sc
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@ -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