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.

5 files changed, 64 insertions, 7 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 608ea54..82005a4 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,24 @@
+2021-05-26  H.J. Lu  <hongjiu.lu@intel.com>
+
+	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.
+
 2021-05-26  Nelson Chu  <nelson.chu@sifive.com>
 
 	* elfxx-riscv.h (check_unknown_prefixed_ext): New bool.
diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
index 4451f9b..c68741a 100644
--- a/bfd/elf32-i386.c
+++ b/bfd/elf32-i386.c
@@ -22,6 +22,7 @@
 #include "elf-vxworks.h"
 #include "dwarf2.h"
 #include "opcode/i386.h"
+#include "libiberty.h"
 
 /* 386 uses REL relocations instead of RELA.  */
 #define USE_REL	1
@@ -175,10 +176,14 @@ static reloc_howto_type elf_howto_table[]=
 	 false,			/* partial_inplace */
 	 0,			/* src_mask */
 	 0,			/* dst_mask */
-	 false)			/* pcrel_offset */
+	 false),		/* pcrel_offset */
 
 #define R_386_vt (R_386_GNU_VTENTRY + 1 - R_386_vt_offset)
 
+/* Use complain_overflow_bitfield on R_386_PC16 for code16.  */
+  HOWTO(R_386_PC16, 0, 1, 16, true, 0, complain_overflow_bitfield,
+	bfd_elf_generic_reloc, "R_386_PC16",
+	true, 0xffff, 0xffff, true)
 };
 
 #define X86_PCREL_TYPE_P(TYPE) ((TYPE) == R_386_PC32)
@@ -369,7 +374,7 @@ elf_i386_reloc_name_lookup (bfd *abfd ATTRIBUTE_UNUSED,
 }
 
 static reloc_howto_type *
-elf_i386_rtype_to_howto (unsigned r_type)
+elf_i386_rtype_to_howto (bfd *abfd, unsigned r_type)
 {
   unsigned int indx;
 
@@ -384,6 +389,11 @@ elf_i386_rtype_to_howto (unsigned r_type)
   /* PR 17512: file: 0f67f69d.  */
   if (elf_howto_table [indx].type != r_type)
     return NULL;
+
+  /* Use complain_overflow_bitfield on R_386_PC16 for code16.  */
+  if (r_type == (unsigned int) R_386_PC16 && elf_x86_has_code16 (abfd))
+    indx = ARRAY_SIZE (elf_howto_table) - 1;
+
   return &elf_howto_table[indx];
 }
 
@@ -394,7 +404,8 @@ elf_i386_info_to_howto_rel (bfd *abfd,
 {
   unsigned int r_type = ELF32_R_TYPE (dst->r_info);
 
-  if ((cache_ptr->howto = elf_i386_rtype_to_howto (r_type)) == NULL)
+  if ((cache_ptr->howto = elf_i386_rtype_to_howto (abfd, r_type))
+      == NULL)
     {
       /* xgettext:c-format */
       _bfd_error_handler (_("%pB: unsupported relocation type %#x"),
@@ -1142,8 +1153,8 @@ elf_i386_tls_transition (struct bfd_link_info *info, bfd *abfd,
       reloc_howto_type *from, *to;
       const char *name;
 
-      from = elf_i386_rtype_to_howto (from_type);
-      to = elf_i386_rtype_to_howto (to_type);
+      from = elf_i386_rtype_to_howto (abfd, from_type);
+      to = elf_i386_rtype_to_howto (abfd, to_type);
 
       if (h)
 	name = h->root.root.string;
@@ -2074,7 +2085,7 @@ elf_i386_relocate_section (bfd *output_bfd,
 	  continue;
 	}
 
-      howto = elf_i386_rtype_to_howto (r_type);
+      howto = elf_i386_rtype_to_howto (input_bfd, r_type);
       if (howto == NULL)
 	return _bfd_unrecognized_reloc (input_bfd, input_section, r_type);
 
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index d0c994e..d420561 100644
--- a/bfd/elf64-x86-64.c
+++ b/bfd/elf64-x86-64.c
@@ -187,6 +187,10 @@ static reloc_howto_type x86_64_elf_howto_table[] =
 	 _bfd_elf_rel_vtable_reloc_fn, "R_X86_64_GNU_VTENTRY", false, 0, 0,
 	 false),
 
+/* Use complain_overflow_bitfield on R_X86_64_PC16 for code16.  */
+  HOWTO(R_X86_64_PC16, 0, 1, 16, true, 0, complain_overflow_bitfield,
+	bfd_elf_generic_reloc, "R_X86_64_PC16", false, 0, 0xffff, true),
+
 /* Use complain_overflow_bitfield on R_X86_64_32 for x32.  */
   HOWTO(R_X86_64_32, 0, 2, 32, false, 0, complain_overflow_bitfield,
 	bfd_elf_generic_reloc, "R_X86_64_32", false, 0, 0xffffffff,
@@ -270,6 +274,14 @@ elf_x86_64_rtype_to_howto (bfd *abfd, unsigned r_type)
       else
 	i = ARRAY_SIZE (x86_64_elf_howto_table) - 1;
     }
+  else if (r_type == (unsigned int) R_X86_64_PC16)
+    {
+      /* Use complain_overflow_bitfield on R_X86_64_PC16 for code16.  */
+      if (elf_x86_has_code16 (abfd))
+	i = ARRAY_SIZE (x86_64_elf_howto_table) - 2;
+      else
+	i = r_type;
+    }
   else if (r_type < (unsigned int) R_X86_64_GNU_VTINHERIT
 	   || r_type >= (unsigned int) R_X86_64_max)
     {
diff --git a/bfd/elfxx-x86.c b/bfd/elfxx-x86.c
index 62d516a..29dc7f0 100644
--- a/bfd/elfxx-x86.c
+++ b/bfd/elfxx-x86.c
@@ -2353,6 +2353,7 @@ _bfd_x86_elf_parse_gnu_properties (bfd *abfd, unsigned int type,
       || (type >= GNU_PROPERTY_X86_UINT32_OR_AND_LO
 	  && type <= GNU_PROPERTY_X86_UINT32_OR_AND_HI))
     {
+      unsigned int number;
       if (datasz != 4)
 	{
 	  _bfd_error_handler
@@ -2361,7 +2362,13 @@ _bfd_x86_elf_parse_gnu_properties (bfd *abfd, unsigned int type,
 	  return property_corrupt;
 	}
       prop = _bfd_elf_get_property (abfd, type, datasz);
-      prop->u.number |= bfd_h_get_32 (abfd, ptr);
+      number = bfd_h_get_32 (abfd, ptr);
+      if ((abfd->flags
+	   & (DYNAMIC | BFD_LINKER_CREATED | BFD_PLUGIN)) == 0
+	  && type == GNU_PROPERTY_X86_FEATURE_2_USED
+	  && (number & GNU_PROPERTY_X86_FEATURE_2_CODE16) != 0)
+	elf_x86_has_code16 (abfd) = 1;
+      prop->u.number |= number;
       prop->pr_kind = property_number;
       return property_number;
     }
diff --git a/bfd/elfxx-x86.h b/bfd/elfxx-x86.h
index db11327..e834430 100644
--- a/bfd/elfxx-x86.h
+++ b/bfd/elfxx-x86.h
@@ -549,6 +549,9 @@ struct elf_x86_obj_tdata
 
   /* GOTPLT entries for TLS descriptors.  */
   bfd_vma *local_tlsdesc_gotent;
+
+  /* Set if the objec file has 16-bit code.  */
+  unsigned int has_code16 : 1;
 };
 
 enum elf_x86_plt_type
@@ -584,6 +587,9 @@ struct elf_x86_plt
 #define elf_x86_local_tlsdesc_gotent(abfd) \
   (elf_x86_tdata (abfd)->local_tlsdesc_gotent)
 
+#define elf_x86_has_code16(abfd) \
+  (elf_x86_tdata (abfd)->has_code16)
+
 #define elf_x86_compute_jump_table_size(htab) \
   ((htab)->elf.srelplt->reloc_count * (htab)->got_entry_size)