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.

4 files changed, 29 insertions, 0 deletions

diff --git a/gas/testsuite/gas/i386/code16-2.d b/gas/testsuite/gas/i386/code16-2.d
new file mode 100644
index 0000000..37b66c8
--- /dev/null
+++ b/gas/testsuite/gas/i386/code16-2.d
@@ -0,0 +1,8 @@
+#name: i386 code16 2
+#as: -mx86-used-note=no --generate-missing-build-notes=no
+#readelf: -n
+
+Displaying notes found in: .note.gnu.property
+[ 	]+Owner[ 	]+Data size[ 	]+Description
+  GNU                  0x[0-9a-f]+	NT_GNU_PROPERTY_TYPE_0
+      Properties: x86 feature used: x86, CODE16
diff --git a/gas/testsuite/gas/i386/code16-2.s b/gas/testsuite/gas/i386/code16-2.s
new file mode 100644
index 0000000..66e5d55
--- /dev/null
+++ b/gas/testsuite/gas/i386/code16-2.s
@@ -0,0 +1,10 @@
+	.code16gcc
+	.text
+	.section	.text.default_process_op.isra.0,"ax",@progbits
+	.type	default_process_op.isra.0, @function
+default_process_op.isra.0:
+	ret
+	.section	.text.mpt_scsi_process_op,"ax",@progbits
+	.type	mpt_scsi_process_op, @function
+mpt_scsi_process_op:
+	jmp	default_process_op.isra.0
diff --git a/gas/testsuite/gas/i386/i386.exp b/gas/testsuite/gas/i386/i386.exp
index 39010bd..a459c6f 100644
--- a/gas/testsuite/gas/i386/i386.exp
+++ b/gas/testsuite/gas/i386/i386.exp
@@ -734,6 +734,7 @@ if {[is_elf_format] || [istarget "*-*-vxworks*"]} then {
     run_dump_test "property-ldmxcsr"
     run_dump_test "property-vldmxcsr"
     run_dump_test "property-vzeroall"
+    run_dump_test "code16-2"
 
     if {![istarget "*-*-dragonfly*"]
 	&& ![istarget "*-*-gnu*"]
@@ -1298,6 +1299,7 @@ if [gas_64_check] then {
 	run_dump_test "x86-64-property-8"
 	run_dump_test "x86-64-property-9"
 	run_dump_test "x86-64-property-14"
+	run_dump_test "x86-64-code16-2"
 
 	if {[istarget "*-*-linux*"]} then {
 	    run_dump_test "x86-64-align-branch-3"
diff --git a/gas/testsuite/gas/i386/x86-64-code16-2.d b/gas/testsuite/gas/i386/x86-64-code16-2.d
new file mode 100644
index 0000000..dbabd67
--- /dev/null
+++ b/gas/testsuite/gas/i386/x86-64-code16-2.d
@@ -0,0 +1,9 @@
+#source: code16-2.s
+#name: x86-64 code16 2
+#as: -mx86-used-note=no --generate-missing-build-notes=no
+#readelf: -n
+
+Displaying notes found in: .note.gnu.property
+[ 	]+Owner[ 	]+Data size[ 	]+Description
+  GNU                  0x[0-9a-f]+	NT_GNU_PROPERTY_TYPE_0
+      Properties: x86 feature used: x86, CODE16