x86-64: Add -z mark-plt and -z nomark-plt

The PLT entry in executables and shared libraries contains an indirect
branch, like

 	jmp *foo@GOTPCREL(%rip)
	push $index_foo
	jmp .PLT0

or

	endbr64
 	jmp *foo@GOTPCREL(%rip)
 	NOP padding

which is used to branch to the function, foo, defined in another object.
Each R_X86_64_JUMP_SLOT relocation has a corresponding PLT entry.

The dynamic tags have been added to the x86-64 psABI to mark such PLT
entries:

https://gitlab.com/x86-psABIs/x86-64-ABI/-/commit/6d824a52a42d173eb838b879616c1be5870b593e

Add an x86-64 linker option, -z mark-plt, to mark PLT entries with

 #define DT_X86_64_PLT     (DT_LOPROC + 0)
 #define DT_X86_64_PLTSZ   (DT_LOPROC + 1)
 #define DT_X86_64_PLTENT  (DT_LOPROC + 3)

1. DT_X86_64_PLT: The address of the procedure linkage table.
2. DT_X86_64_PLTSZ: The total size, in bytes, of the procedure linkage
table.
3. DT_X86_64_PLTENT: The size, in bytes, of a procedure linkage table
entry.

and set the r_addend field of the R_X86_64_JUMP_SLOT relocation to the
memory offset of the indirect branch instruction.  The dynamic linker
can use these tags to update the PLT section to direct branch.

bfd/

	* elf-linker-x86.h (elf_linker_x86_params): Add mark_plt.
	* elf64-x86-64.c (elf_x86_64_finish_dynamic_symbol): Set the
	r_addend of R_X86_64_JUMP_SLOT to the indirect branch offset
	in PLT entry for -z mark-plt.
	* elfxx-x86.c (_bfd_x86_elf_size_dynamic_sections): Add
	DT_X86_64_PLT, DT_X86_64_PLTSZ and DT_X86_64_PLTENT for
	-z mark-plt.
	(_bfd_x86_elf_finish_dynamic_sections): Set DT_X86_64_PLT,
	DT_X86_64_PLTSZ and DT_X86_64_PLTENT.
	(_bfd_x86_elf_get_synthetic_symtab): Ignore addend for
	JUMP_SLOT relocation.
	(_bfd_x86_elf_link_setup_gnu_properties): Set
	plt_indirect_branch_offset.
	* elfxx-x86.h (elf_x86_plt_layout): Add plt_indirect_branch_offset.

binutils/

	* readelf.c (get_x86_64_dynamic_type): New function.
	(get_dynamic_type): Call get_x86_64_dynamic_type.

include/

	* elf/x86-64.h (DT_X86_64_PLT): New.
	(DT_X86_64_PLTSZ): Likewise.
	(DT_X86_64_PLTENT): Likewise.

ld/

	* ld.texi: Document -z mark-plt and -z nomark-plt.
	* emulparams/elf32_x86_64.sh: Source x86-64-plt.sh.
	* emulparams/elf_x86_64.sh: Likewise.
	* emulparams/x86-64-plt.sh: New file.
	* testsuite/ld-x86-64/mark-plt-1.s: Likewise.
	* testsuite/ld-x86-64/mark-plt-1a-x32.d: Likewise.
	* testsuite/ld-x86-64/mark-plt-1a.d: Likewise.
	* testsuite/ld-x86-64/mark-plt-1b-x32.d: Likewise.
	* testsuite/ld-x86-64/mark-plt-1b.d: Likewise.
	* testsuite/ld-x86-64/mark-plt-1c-x32.d: Likewise.
	* testsuite/ld-x86-64/mark-plt-1c.d: Likewise.
	* testsuite/ld-x86-64/mark-plt-1d-x32.d: Likewise.
	* testsuite/ld-x86-64/mark-plt-1d.d: Likewise.
	* testsuite/ld-x86-64/x86-64.exp: Run -z mark-plt tests.

4 files changed, 58 insertions, 2 deletions

diff --git a/bfd/elf-linker-x86.h b/bfd/elf-linker-x86.h
index e39dbf2..1e6ecb1 100644
--- a/bfd/elf-linker-x86.h
+++ b/bfd/elf-linker-x86.h
@@ -61,6 +61,9 @@ struct elf_linker_x86_params
   /* Report relative relocations.  */
   unsigned int report_relative_reloc : 1;
 
+  /* Mark PLT with dynamic tags.  */
+  unsigned int mark_plt : 1;
+
   /* X86-64 ISA level needed.  */
   unsigned int isa_level;
 
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index e7a0a91..3b7a8ae 100644
--- a/bfd/elf64-x86-64.c
+++ b/bfd/elf64-x86-64.c
@@ -4455,7 +4455,12 @@ elf_x86_64_finish_dynamic_symbol (bfd *output_bfd,
 	  else
 	    {
 	      rela.r_info = htab->r_info (h->dynindx, R_X86_64_JUMP_SLOT);
-	      rela.r_addend = 0;
+	      if (htab->params->mark_plt)
+		rela.r_addend = (resolved_plt->output_section->vma
+				 + plt_offset
+				 + htab->plt.plt_indirect_branch_offset);
+	      else
+		rela.r_addend = 0;
 	      plt_index = htab->next_jump_slot_index++;
 	    }
 
diff --git a/bfd/elfxx-x86.c b/bfd/elfxx-x86.c
index 103559d..58bd76d 100644
--- a/bfd/elfxx-x86.c
+++ b/bfd/elfxx-x86.c
@@ -2525,6 +2525,19 @@ _bfd_x86_elf_size_dynamic_sections (bfd *output_bfd,
 	}
     }
 
+  asection *resolved_plt = NULL;
+
+  if (htab->params->mark_plt && htab->elf.dynamic_sections_created)
+    {
+      if (htab->plt_second != NULL)
+	resolved_plt = htab->plt_second;
+      else
+	resolved_plt = htab->elf.splt;
+
+      if (resolved_plt != NULL && resolved_plt->size == 0)
+	resolved_plt = NULL;
+    }
+
   /* We now have determined the sizes of the various dynamic sections.
      Allocate memory for them.  */
   relocs = false;
@@ -2673,6 +2686,12 @@ _bfd_x86_elf_size_dynamic_sections (bfd *output_bfd,
 	_bfd_x86_elf_write_sframe_plt (output_bfd, info, SFRAME_PLT_SEC);
     }
 
+  if (resolved_plt != NULL
+      && (!_bfd_elf_add_dynamic_entry (info, DT_X86_64_PLT, 0)
+	  || !_bfd_elf_add_dynamic_entry (info, DT_X86_64_PLTSZ, 0)
+	  || !_bfd_elf_add_dynamic_entry (info, DT_X86_64_PLTENT, 0)))
+    return false;
+
   return _bfd_elf_maybe_vxworks_add_dynamic_tags (output_bfd, info,
 						  relocs);
 }
@@ -2747,6 +2766,12 @@ _bfd_x86_elf_finish_dynamic_sections (bfd *output_bfd,
   if (sdyn == NULL || htab->elf.sgot == NULL)
     abort ();
 
+  asection *resolved_plt;
+  if (htab->plt_second != NULL)
+    resolved_plt = htab->plt_second;
+  else
+    resolved_plt = htab->elf.splt;
+
   sizeof_dyn = bed->s->sizeof_dyn;
   dyncon = sdyn->contents;
   dynconend = sdyn->contents + sdyn->size;
@@ -2791,6 +2816,19 @@ _bfd_x86_elf_finish_dynamic_sections (bfd *output_bfd,
 	  dyn.d_un.d_ptr = s->output_section->vma + s->output_offset
 	    + htab->elf.tlsdesc_got;
 	  break;
+
+	case DT_X86_64_PLT:
+	  s = resolved_plt->output_section;
+	  dyn.d_un.d_ptr = s->output_section->vma + s->output_offset;
+	  break;
+
+	case DT_X86_64_PLTSZ:
+	  dyn.d_un.d_val = resolved_plt->size;
+	  break;
+
+	case DT_X86_64_PLTENT:
+	  dyn.d_un.d_ptr = htab->plt.plt_entry_size;
+	  break;
 	}
 
       (*bed->s->swap_dyn_out) (output_bfd, &dyn, dyncon);
@@ -3561,6 +3599,7 @@ _bfd_x86_elf_get_synthetic_symtab (bfd *abfd,
   bfd_vma (*get_plt_got_vma) (struct elf_x86_plt *, bfd_vma, bfd_vma,
 			      bfd_vma);
   bool (*valid_plt_reloc_p) (unsigned int);
+  unsigned int jump_slot_reloc;
 
   dynrelbuf = NULL;
   if (count == 0)
@@ -3601,11 +3640,13 @@ _bfd_x86_elf_get_synthetic_symtab (bfd *abfd,
     {
       get_plt_got_vma = elf_x86_64_get_plt_got_vma;
       valid_plt_reloc_p = elf_x86_64_valid_plt_reloc_p;
+      jump_slot_reloc = R_X86_64_JUMP_SLOT;
     }
   else
     {
       get_plt_got_vma = elf_i386_get_plt_got_vma;
       valid_plt_reloc_p = elf_i386_valid_plt_reloc_p;
+      jump_slot_reloc = R_386_JUMP_SLOT;
       if (got_addr)
 	{
 	  /* Check .got.plt and then .got to get the _GLOBAL_OFFSET_TABLE_
@@ -3710,7 +3751,9 @@ _bfd_x86_elf_get_synthetic_symtab (bfd *abfd,
 		len = strlen ((*p->sym_ptr_ptr)->name);
 		memcpy (names, (*p->sym_ptr_ptr)->name, len);
 		names += len;
-		if (p->addend != 0)
+		/* There may be JUMP_SLOT and IRELATIVE relocations.
+		   JUMP_SLOT r_addend should be ignored.  */
+		if (p->addend != 0 && p->howto->type != jump_slot_reloc)
 		  {
 		    char buf[30], *a;
 
@@ -4275,6 +4318,7 @@ _bfd_x86_elf_link_setup_gnu_properties
      still be used with LD_AUDIT or LD_PROFILE if PLT entry is used for
      canonical function address.  */
   htab->plt.has_plt0 = 1;
+  htab->plt.plt_indirect_branch_offset = 0;
   normal_target = htab->elf.target_os == is_normal;
 
   if (normal_target)
@@ -4283,6 +4327,7 @@ _bfd_x86_elf_link_setup_gnu_properties
 	{
 	  htab->lazy_plt = init_table->lazy_ibt_plt;
 	  htab->non_lazy_plt = init_table->non_lazy_ibt_plt;
+	  htab->plt.plt_indirect_branch_offset = 4;
 	}
       else
 	{
diff --git a/bfd/elfxx-x86.h b/bfd/elfxx-x86.h
index 3b4644c..0bc966b 100644
--- a/bfd/elfxx-x86.h
+++ b/bfd/elfxx-x86.h
@@ -502,6 +502,9 @@ struct elf_x86_plt_layout
   /* 1 has PLT0.  */
   unsigned int has_plt0;
 
+  /* Offset of indirect branch in plt_entry.  */
+  unsigned int plt_indirect_branch_offset;
+
   /* Offsets into plt_entry that are to be replaced with...  */
   unsigned int plt_got_offset;    /* ... address of this symbol in .got. */