path: root/bfd/elf64-bpf.c

/* Linux bpf specific support for 64-bit ELF
   Copyright (C) 2019-2023 Free Software Foundation, Inc.
   Contributed by Oracle Inc.

   This file is part of BFD, the Binary File Descriptor library.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
   MA 02110-1301, USA.  */

#include "sysdep.h"
#include "bfd.h"
#include "libbfd.h"
#include "elf-bfd.h"
#include "elf/bpf.h"
#include "libiberty.h"

/* In case we're on a 32-bit machine, construct a 64-bit "-1" value.  */
#define MINUS_ONE (~ (bfd_vma) 0)

#define BASEADDR(SEC)	((SEC)->output_section->vma + (SEC)->output_offset)

static bfd_reloc_status_type bpf_elf_generic_reloc
  (bfd *, arelent *, asymbol *, void *, asection *, bfd *, char **);

#undef BPF_HOWTO
#define BPF_HOWTO(type, right, size, bits, pcrel, left, ovf, func, name,   \
		  inplace, src_mask, dst_mask, pcrel_off)                  \
	type##_IDX,
enum bpf_reloc_index {
  R_BPF_INVALID_IDX = -1,
#include "bpf-reloc.def"
  R_BPF_SIZE
};
#undef BPF_HOWTO

/* Relocation tables.  */
#define BPF_HOWTO(...) HOWTO(__VA_ARGS__),
static reloc_howto_type bpf_elf_howto_table [] =
{
  #include "bpf-reloc.def"
};
#undef AHOW
#undef BPF_HOWTO

#define BPF_HOWTO(type, right, size, bits, pcrel, left, ovf, func, name,   \
		  inplace, src_mask, dst_mask, pcrel_off)                  \
    case type: { return type##_IDX; }
static enum bpf_reloc_index
bpf_index_for_rtype(unsigned int r_type)
{
  switch(r_type) {
#include "bpf-reloc.def"
    default:
      /* Unreachable code. */
      BFD_ASSERT(0);
      return -1;
  };
}

/* Map BFD reloc types to bpf ELF reloc types.  */

static reloc_howto_type *
bpf_reloc_type_lookup (bfd * abfd ATTRIBUTE_UNUSED,
                        bfd_reloc_code_real_type code)
{
  switch (code)
    {
    case BFD_RELOC_NONE:
      return &bpf_elf_howto_table[ (int) R_BPF_NONE_IDX];

    case BFD_RELOC_32:
      return &bpf_elf_howto_table[ (int) R_BPF_64_ABS32_IDX];
    case BFD_RELOC_64:
      return &bpf_elf_howto_table[ (int) R_BPF_64_ABS64_IDX];

    case BFD_RELOC_BPF_64:
      return &bpf_elf_howto_table[ (int) R_BPF_64_64_IDX];
    case BFD_RELOC_BPF_DISP32:
    case BFD_RELOC_BPF_DISPCALL32:
      return &bpf_elf_howto_table[ (int) R_BPF_64_32_IDX];
    case BFD_RELOC_BPF_DISP16:
      return &bpf_elf_howto_table[ (int) R_BPF_GNU_64_16_IDX];

    default:
      /* Pacify gcc -Wall.  */
      return NULL;
    }
  return NULL;
}

/* Map BFD reloc names to bpf ELF reloc names.  */

static reloc_howto_type *
bpf_reloc_name_lookup (bfd *abfd ATTRIBUTE_UNUSED, const char *r_name)
{
  unsigned int i;

  for (i = 0; i < R_BPF_SIZE; i++)
    if (bpf_elf_howto_table[i].name != NULL
	&& strcasecmp (bpf_elf_howto_table[i].name, r_name) == 0)
      return &bpf_elf_howto_table[i];

  return NULL;
}

/* Set the howto pointer for a bpf reloc.  */

static bool
bpf_info_to_howto (bfd *abfd, arelent *bfd_reloc,
                    Elf_Internal_Rela *elf_reloc)
{
  unsigned int r_type;
  unsigned int i;
  r_type = ELF64_R_TYPE (elf_reloc->r_info);

  i = bpf_index_for_rtype(r_type);
  if (i == (unsigned int) -1)
    {
      /* xgettext:c-format */
      _bfd_error_handler (_("%pB: unsupported relocation type %#x"),
                          abfd, r_type);
      bfd_set_error (bfd_error_bad_value);
      return false;
    }

  bfd_reloc->howto = &bpf_elf_howto_table [i];
  return true;
}

/* Relocate an eBPF ELF section.

   The RELOCATE_SECTION function is called by the new ELF backend linker
   to handle the relocations for a section.

   The relocs are always passed as Rela structures; if the section
   actually uses Rel structures, the r_addend field will always be
   zero.

   This function is responsible for adjusting the section contents as
   necessary, and (if using Rela relocs and generating a relocatable
   output file) adjusting the reloc addend as necessary.

   This function does not have to worry about setting the reloc
   address or the reloc symbol index.

   LOCAL_SYMS is a pointer to the swapped in local symbols.

   LOCAL_SECTIONS is an array giving the section in the input file
   corresponding to the st_shndx field of each local symbol.

   The global hash table entry for the global symbols can be found
   via elf_sym_hashes (input_bfd).

   When generating relocatable output, this function must handle
   STB_LOCAL/STT_SECTION symbols specially.  The output symbol is
   going to be the section symbol corresponding to the output
   section, which means that the addend must be adjusted
   accordingly.  */

#define sec_addr(sec) ((sec)->output_section->vma + (sec)->output_offset)

static int
bpf_elf_relocate_section (bfd *output_bfd ATTRIBUTE_UNUSED,
                          struct bfd_link_info *info,
                          bfd *input_bfd,
                          asection *input_section,
                          bfd_byte *contents,
                          Elf_Internal_Rela *relocs,
                          Elf_Internal_Sym *local_syms,
                          asection **local_sections)
{
  Elf_Internal_Shdr *symtab_hdr;
  struct elf_link_hash_entry **sym_hashes;
  Elf_Internal_Rela *rel;
  Elf_Internal_Rela *relend;

  symtab_hdr = & elf_tdata (input_bfd)->symtab_hdr;
  sym_hashes = elf_sym_hashes (input_bfd);
  relend     = relocs + input_section->reloc_count;

  for (rel = relocs; rel < relend; rel ++)
    {
      reloc_howto_type *	   howto;
      unsigned int		   howto_index;
      unsigned long		   r_symndx;
      Elf_Internal_Sym *	   sym;
      asection *		   sec;
      struct elf_link_hash_entry * h;
      bfd_vma			   relocation;
      bfd_reloc_status_type	   r;
      const char *		   name = NULL;
      int			   r_type ATTRIBUTE_UNUSED;
      bfd_signed_vma               addend;
      bfd_byte                   * where;

      r_type = ELF64_R_TYPE (rel->r_info);
      r_symndx = ELF64_R_SYM (rel->r_info);

      howto_index = bpf_index_for_rtype (ELF64_R_TYPE (rel->r_info));
      howto  = &bpf_elf_howto_table[howto_index];
      h      = NULL;
      sym    = NULL;
      sec    = NULL;
      where  = contents + rel->r_offset;

      if (r_symndx < symtab_hdr->sh_info)
	{
	  sym = local_syms + r_symndx;
	  sec = local_sections [r_symndx];
	  relocation = BASEADDR (sec) + sym->st_value;

	  name = bfd_elf_string_from_elf_section
	    (input_bfd, symtab_hdr->sh_link, sym->st_name);
	  name = name == NULL ? bfd_section_name (sec) : name;
	}
      else
	{
	  bool warned ATTRIBUTE_UNUSED;
	  bool unresolved_reloc ATTRIBUTE_UNUSED;
	  bool ignored ATTRIBUTE_UNUSED;

	  RELOC_FOR_GLOBAL_SYMBOL (info, input_bfd, input_section, rel,
				   r_symndx, symtab_hdr, sym_hashes,
				   h, sec, relocation,
				   unresolved_reloc, warned, ignored);

	  name = h->root.root.string;
	}

      if (sec != NULL && discarded_section (sec))
	RELOC_AGAINST_DISCARDED_SECTION (info, input_bfd, input_section,
					 rel, 1, relend, howto, 0, contents);

      if (bfd_link_relocatable (info))
	continue;

      switch (howto->type)
        {
	case R_BPF_64_32:
          {
            /* Make the relocation PC-relative, and change its unit to
               64-bit words.  Note we need *signed* arithmetic
               here.  */
            relocation = ((bfd_signed_vma) relocation
			  - (sec_addr (input_section) + rel->r_offset));
            relocation = (bfd_signed_vma) relocation / 8;
            
            /* Get the addend from the instruction and apply it.  */
            addend = bfd_get (howto->bitsize, input_bfd,
                              contents + rel->r_offset
                              + (howto->bitsize == 16 ? 2 : 4));
                              
            if ((addend & (((~howto->src_mask) >> 1) & howto->src_mask)) != 0)
              addend -= (((~howto->src_mask) >> 1) & howto->src_mask) << 1;
            relocation += addend;

            /* Write out the relocated value.  */
            bfd_put (howto->bitsize, input_bfd, relocation,
                     contents + rel->r_offset
                     + (howto->bitsize == 16 ? 2 : 4));

            r = bfd_reloc_ok;
            break;
          }
	case R_BPF_64_ABS64:
	case R_BPF_64_ABS32:
	  {
	    addend = bfd_get (howto->bitsize, input_bfd, where);
	    relocation += addend;
	    bfd_put (howto->bitsize, input_bfd, relocation, where);

	    r = bfd_reloc_ok;
	    break;
	  }
	case R_BPF_64_64:
          {
            /*
                LDDW instructions are 128 bits long, with a 64-bit immediate.
                The lower 32 bits of the immediate are in the same position
                as the imm32 field of other instructions.
                The upper 32 bits of the immediate are stored at the end of
                the instruction.
             */


            /* Get the addend. The upper and lower 32 bits are split.
               'where' is the beginning of the 16-byte instruction. */
            addend = bfd_get_32 (input_bfd, where + 4);
            addend |= (bfd_get_32 (input_bfd, where + 12) << 32);

            relocation += addend;

            bfd_put_32 (input_bfd, (relocation & 0xFFFFFFFF), where + 4);
            bfd_put_32 (input_bfd, (relocation >> 32), where + 12);
            r = bfd_reloc_ok;
            break;
          }
        default:
	  r = bfd_reloc_notsupported;
        }

      if (r == bfd_reloc_ok)
	  r = bfd_check_overflow (howto->complain_on_overflow,
				  howto->bitsize,
				  howto->rightshift,
				  64, relocation);

      if (r != bfd_reloc_ok)
	{
	  const char * msg = NULL;

	  switch (r)
	    {
	    case bfd_reloc_overflow:
	      (*info->callbacks->reloc_overflow)
		(info, (h ? &h->root : NULL), name, howto->name,
		 (bfd_vma) 0, input_bfd, input_section, rel->r_offset);
	      break;

	    case bfd_reloc_undefined:
	      (*info->callbacks->undefined_symbol)
		(info, name, input_bfd, input_section, rel->r_offset, true);
	      break;

	    case bfd_reloc_outofrange:
	      msg = _("internal error: out of range error");
	      break;

	    case bfd_reloc_notsupported:
	      if (sym != NULL) /* Only if it's not an unresolved symbol.  */
                msg = _("internal error: relocation not supported");
	      break;

	    case bfd_reloc_dangerous:
	      msg = _("internal error: dangerous relocation");
	      break;

	    default:
	      msg = _("internal error: unknown error");
	      break;
	    }

	  if (msg)
	    (*info->callbacks->warning) (info, msg, name, input_bfd,
					 input_section, rel->r_offset);
	}
    }

  return true;
}

/* Merge backend specific data from an object file to the output
   object file when linking.  */

static bool
elf64_bpf_merge_private_bfd_data (bfd *ibfd, struct bfd_link_info *info)
{
  /* Check if we have the same endianness.  */
  if (! _bfd_generic_verify_endian_match (ibfd, info))
    return false;

  return true;
}

/* A generic howto special function for installing BPF relocations.
   This function will be called by the assembler (via bfd_install_relocation),
   and by various get_relocated_section_contents functions.
   At link time, bpf_elf_relocate_section will resolve the final relocations.

   BPF instructions are always big endian, and this approach avoids problems in
   bfd_install_relocation.  */

static bfd_reloc_status_type
bpf_elf_generic_reloc (bfd *abfd, arelent *reloc_entry, asymbol *symbol,
		       void *data, asection *input_section,
		       bfd *output_bfd ATTRIBUTE_UNUSED,
		       char **error_message ATTRIBUTE_UNUSED)
{

  bfd_signed_vma relocation;
  bfd_reloc_status_type status;
  bfd_byte *where;

  /* Sanity check that the address is in range.  */
  bfd_size_type end = bfd_get_section_limit_octets (abfd, input_section);
  bfd_size_type reloc_size;
  if (reloc_entry->howto->type == R_BPF_64_64)
    reloc_size = 16;
  else
    reloc_size = (reloc_entry->howto->bitsize
		  + reloc_entry->howto->bitpos) / 8;

  if (reloc_entry->address > end
      || end - reloc_entry->address < reloc_size)
    return bfd_reloc_outofrange;

  /*  Get the symbol value.  */
  if (bfd_is_com_section (symbol->section))
    relocation = 0;
  else
    relocation = symbol->value;

  if (symbol->flags & BSF_SECTION_SYM)
    /* Relocation against a section symbol: add in the section base address.  */
    relocation += BASEADDR (symbol->section);

  relocation += reloc_entry->addend;

  where = (bfd_byte *) data + reloc_entry->address;

  status = bfd_check_overflow (reloc_entry->howto->complain_on_overflow,
			       reloc_entry->howto->bitsize,
			       reloc_entry->howto->rightshift, 64, relocation);

  if (status != bfd_reloc_ok)
    return status;

  /* Now finally install the relocation.  */
  if (reloc_entry->howto->type == R_BPF_64_64)
    {
      /* lddw is a 128-bit (!) instruction that allows loading a 64-bit
	 immediate into a register. the immediate is split in half, with the
	 lower 32 bits in the same position as the imm32 field of other
	 instructions, and the upper 32 bits placed at the very end of the
	 instruction. that is, there are 32 unused bits between them. */

      bfd_put_32 (abfd, (relocation & 0xFFFFFFFF), where + 4);
      bfd_put_32 (abfd, (relocation >> 32), where + 12);
    }
  else
    {
      /* For other kinds of relocations, the relocated value simply goes
	 BITPOS bits from the start of the entry. This is always a multiple
	 of 8, i.e. whole bytes.  */
      bfd_put (reloc_entry->howto->bitsize, abfd, relocation,
	       where + reloc_entry->howto->bitpos / 8);
    }

  reloc_entry->addend = relocation;
  reloc_entry->address += input_section->output_offset;

  return bfd_reloc_ok;
}


/* The macros below configure the architecture.  */

#define TARGET_LITTLE_SYM bpf_elf64_le_vec
#define TARGET_LITTLE_NAME "elf64-bpfle"

#define TARGET_BIG_SYM bpf_elf64_be_vec
#define TARGET_BIG_NAME "elf64-bpfbe"

#define ELF_ARCH bfd_arch_bpf
#define ELF_MACHINE_CODE EM_BPF

#define ELF_MAXPAGESIZE 0x100000

#define elf_info_to_howto_rel bpf_info_to_howto
#define elf_info_to_howto bpf_info_to_howto

#define elf_backend_may_use_rel_p		1
#define elf_backend_may_use_rela_p		0
#define elf_backend_default_use_rela_p		0
#define elf_backend_relocate_section		bpf_elf_relocate_section

#define elf_backend_can_gc_sections		0

#define elf_symbol_leading_char			'_'
#define bfd_elf64_bfd_reloc_type_lookup		bpf_reloc_type_lookup
#define bfd_elf64_bfd_reloc_name_lookup		bpf_reloc_name_lookup

#define bfd_elf64_bfd_merge_private_bfd_data elf64_bpf_merge_private_bfd_data

#include "elf64-target.h"