x86: Propery check PC16 reloc overflow in 16-bit mode instructions

x86: Propery check PC16 reloc overflow in 16-bit mode instructions

commit a7664973b24a242cd9ea17deb5eaf503065fc0bd
Author: Jan Beulich <jbeulich@suse.com>
Date:   Mon Apr 26 10:41:35 2021 +0200

    x86: correct overflow checking for 16-bit PC-relative relocs

caused linker failure when building 16-bit program in a 32-bit ELF
container.  Update GNU_PROPERTY_X86_FEATURE_2_USED with

 #define GNU_PROPERTY_X86_FEATURE_2_CODE16 (1U << 12)

to indicate that 16-bit mode instructions are used in the input object:

https://groups.google.com/g/x86-64-abi/c/UvvXWeHIGMA

to indicate that 16-bit mode instructions are used in the object to
allow linker to properly perform relocation overflow check for 16-bit
PC-relative relocations in 16-bit mode instructions.

1. Update x86 assembler to always generate the GNU property note with
GNU_PROPERTY_X86_FEATURE_2_CODE16 for .code16 in ELF object.
2. Update i386 and x86-64 linkers to use 16-bit PC16 relocations if
input object is marked with GNU_PROPERTY_X86_FEATURE_2_CODE16.

bfd/

	PR ld/27905
	* elf32-i386.c: Include "libiberty.h".
	(elf_howto_table): Add 16-bit R_386_PC16 entry.
	(elf_i386_rtype_to_howto): Add a BFD argument.  Use 16-bit
	R_386_PC16 if input has 16-bit mode instructions.
	(elf_i386_info_to_howto_rel): Update elf_i386_rtype_to_howto
	call.
	(elf_i386_tls_transition): Likewise.
	(elf_i386_relocate_section): Likewise.
	* elf64-x86-64.c (x86_64_elf_howto_table): Add 16-bit
	R_X86_64_PC16 entry.
	(elf_x86_64_rtype_to_howto): Use 16-bit R_X86_64_PC16 if input
	has 16-bit mode instructions.
	* elfxx-x86.c (_bfd_x86_elf_parse_gnu_properties): Set
	elf_x86_has_code16 if relocatable input is marked with
	GNU_PROPERTY_X86_FEATURE_2_CODE16.
	* elfxx-x86.h (elf_x86_obj_tdata): Add has_code16.
	(elf_x86_has_code16): New.

binutils/

	PR ld/27905
	* readelf.c (decode_x86_feature_2): Support
	GNU_PROPERTY_X86_FEATURE_2_CODE16.

gas/

	PR ld/27905
	* config/tc-i386.c (set_code_flag): Update x86_feature_2_used
	with GNU_PROPERTY_X86_FEATURE_2_CODE16 for .code16 in ELF
	object.
	(set_16bit_gcc_code_flag): Likewise.
	(x86_cleanup): Always generate the GNU property note if
	x86_feature_2_used isn't 0.
	* testsuite/gas/i386/code16-2.d: New file.
	* testsuite/gas/i386/code16-2.s: Likewise.
	* testsuite/gas/i386/x86-64-code16-2.d: Likewise.
	* testsuite/gas/i386/i386.exp: Run code16-2 and x86-64-code16-2.

include/

	PR ld/27905
	* elf/common.h (GNU_PROPERTY_X86_FEATURE_2_CODE16): New.

ld/

	PR ld/27905
	* testsuite/ld-i386/code16.d: New file.
	* testsuite/ld-i386/code16.t: Likewise.
	* testsuite/ld-x86-64/code16.d: Likewise.
	* testsuite/ld-x86-64/code16.t: Likewise.
	* testsuite/ld-i386/i386.exp: Run code16.
	* testsuite/ld-x86-64/x86-64.exp: Likewise.