reloc.c

来自「基于4个mips核的noc设计」· C语言 代码 · 共 2,228 行 · 第 1/5 页

/*
TYPEDEF
	arelent_chain

DESCRIPTION

	How relocs are tied together in an <<asection>>:

.typedef struct relent_chain {
.  arelent relent;
.  struct   relent_chain *next;
.} arelent_chain;

*/

/* N_ONES produces N one bits, without overflowing machine arithmetic.  */
#define N_ONES(n) (((((bfd_vma) 1 << ((n) - 1)) - 1) << 1) | 1)

/*
FUNCTION
	bfd_check_overflow

SYNOPSIS
	bfd_reloc_status_type
		bfd_check_overflow
			(enum complain_overflow how,
			 unsigned int bitsize,
			 unsigned int rightshift,
			 unsigned int addrsize,
			 bfd_vma relocation);

DESCRIPTION
	Perform overflow checking on @var{relocation} which has
	@var{bitsize} significant bits and will be shifted right by
	@var{rightshift} bits, on a machine with addresses containing
	@var{addrsize} significant bits.  The result is either of
	@code{bfd_reloc_ok} or @code{bfd_reloc_overflow}.

*/

bfd_reloc_status_type
bfd_check_overflow (how, bitsize, rightshift, addrsize, relocation)
     enum complain_overflow how;
     unsigned int bitsize;
     unsigned int rightshift;
     unsigned int addrsize;
     bfd_vma relocation;
{
  bfd_vma fieldmask, addrmask, signmask, ss, a;
  bfd_reloc_status_type flag = bfd_reloc_ok;

  a = relocation;

  /* Note: BITSIZE should always be <= ADDRSIZE, but in case it's not,
     we'll be permissive: extra bits in the field mask will
     automatically extend the address mask for purposes of the
     overflow check.  */
  fieldmask = N_ONES (bitsize);
  addrmask = N_ONES (addrsize) | fieldmask;

  switch (how)
    {
    case complain_overflow_dont:
      break;

    case complain_overflow_signed:
      /* If any sign bits are set, all sign bits must be set.  That
         is, A must be a valid negative address after shifting.  */
      a = (a & addrmask) >> rightshift;
      signmask = ~ (fieldmask >> 1);
      ss = a & signmask;
      if (ss != 0 && ss != ((addrmask >> rightshift) & signmask))
	flag = bfd_reloc_overflow;
      break;

    case complain_overflow_unsigned:
      /* We have an overflow if the address does not fit in the field.  */
      a = (a & addrmask) >> rightshift;
      if ((a & ~ fieldmask) != 0)
	flag = bfd_reloc_overflow;
      break;

    case complain_overflow_bitfield:
      /* Bitfields are sometimes signed, sometimes unsigned.  We
	 explicitly allow an address wrap too, which means a bitfield
	 of n bits is allowed to store -2**n to 2**n-1.  Thus overflow
	 if the value has some, but not all, bits set outside the
	 field.  */
      a >>= rightshift;
      ss = a & ~ fieldmask;
      if (ss != 0 && ss != (((bfd_vma) -1 >> rightshift) & ~ fieldmask))
	flag = bfd_reloc_overflow;
      break;

    default:
      abort ();
    }

  return flag;
}

/*
FUNCTION
	bfd_perform_relocation

SYNOPSIS
	bfd_reloc_status_type
                bfd_perform_relocation
                        (bfd *abfd,
                         arelent *reloc_entry,
                         PTR data,
                         asection *input_section,
                         bfd *output_bfd,
			 char **error_message);

DESCRIPTION
	If @var{output_bfd} is supplied to this function, the
	generated image will be relocatable; the relocations are
	copied to the output file after they have been changed to
	reflect the new state of the world. There are two ways of
	reflecting the results of partial linkage in an output file:
	by modifying the output data in place, and by modifying the
	relocation record.  Some native formats (e.g., basic a.out and
	basic coff) have no way of specifying an addend in the
	relocation type, so the addend has to go in the output data.
	This is no big deal since in these formats the output data
	slot will always be big enough for the addend. Complex reloc
	types with addends were invented to solve just this problem.
	The @var{error_message} argument is set to an error message if
	this return @code{bfd_reloc_dangerous}.

*/

bfd_reloc_status_type
bfd_perform_relocation (abfd, reloc_entry, data, input_section, output_bfd,
			error_message)
     bfd *abfd;
     arelent *reloc_entry;
     PTR data;
     asection *input_section;
     bfd *output_bfd;
     char **error_message;
{
  bfd_vma relocation;
  bfd_reloc_status_type flag = bfd_reloc_ok;
  bfd_size_type octets = reloc_entry->address * bfd_octets_per_byte (abfd);
  bfd_vma output_base = 0;
  reloc_howto_type *howto = reloc_entry->howto;
  asection *reloc_target_output_section;
  asymbol *symbol;

  symbol = *(reloc_entry->sym_ptr_ptr);
  if (bfd_is_abs_section (symbol->section)
      && output_bfd != (bfd *) NULL)
    {
      reloc_entry->address += input_section->output_offset;
      return bfd_reloc_ok;
    }

  /* If we are not producing relocateable output, return an error if
     the symbol is not defined.  An undefined weak symbol is
     considered to have a value of zero (SVR4 ABI, p. 4-27).  */
  if (bfd_is_und_section (symbol->section)
      && (symbol->flags & BSF_WEAK) == 0
      && output_bfd == (bfd *) NULL)
    flag = bfd_reloc_undefined;

  /* If there is a function supplied to handle this relocation type,
     call it.  It'll return `bfd_reloc_continue' if further processing
     can be done.  */
  if (howto->special_function)
    {
      bfd_reloc_status_type cont;
      cont = howto->special_function (abfd, reloc_entry, symbol, data,
				      input_section, output_bfd,
				      error_message);
      if (cont != bfd_reloc_continue)
	return cont;
    }

  /* Is the address of the relocation really within the section?  */
  if (reloc_entry->address > input_section->_cooked_size /
      bfd_octets_per_byte (abfd))
    return bfd_reloc_outofrange;

  /* Work out which section the relocation is targetted at and the
     initial relocation command value.  */

  /* Get symbol value.  (Common symbols are special.)  */
  if (bfd_is_com_section (symbol->section))
    relocation = 0;
  else
    relocation = symbol->value;

  reloc_target_output_section = symbol->section->output_section;

  /* Convert input-section-relative symbol value to absolute.  */
  if (output_bfd && howto->partial_inplace == false)
    output_base = 0;
  else
    output_base = reloc_target_output_section->vma;

  relocation += output_base + symbol->section->output_offset;

  /* Add in supplied addend.  */
  relocation += reloc_entry->addend;

  /* Here the variable relocation holds the final address of the
     symbol we are relocating against, plus any addend.  */

  if (howto->pc_relative == true)
    {
      /* This is a PC relative relocation.  We want to set RELOCATION
	 to the distance between the address of the symbol and the
	 location.  RELOCATION is already the address of the symbol.

	 We start by subtracting the address of the section containing
	 the location.

	 If pcrel_offset is set, we must further subtract the position
	 of the location within the section.  Some targets arrange for
	 the addend to be the negative of the position of the location
	 within the section; for example, i386-aout does this.  For
	 i386-aout, pcrel_offset is false.  Some other targets do not
	 include the position of the location; for example, m88kbcs,
	 or ELF.  For those targets, pcrel_offset is true.

	 If we are producing relocateable output, then we must ensure
	 that this reloc will be correctly computed when the final
	 relocation is done.  If pcrel_offset is false we want to wind
	 up with the negative of the location within the section,
	 which means we must adjust the existing addend by the change
	 in the location within the section.  If pcrel_offset is true
	 we do not want to adjust the existing addend at all.

	 FIXME: This seems logical to me, but for the case of
	 producing relocateable output it is not what the code
	 actually does.  I don't want to change it, because it seems
	 far too likely that something will break.  */

      relocation -=
	input_section->output_section->vma + input_section->output_offset;

      if (howto->pcrel_offset == true)
	relocation -= reloc_entry->address;
    }

  if (output_bfd != (bfd *) NULL)
    {
      if (howto->partial_inplace == false)
	{
	  /* This is a partial relocation, and we want to apply the relocation
	     to the reloc entry rather than the raw data. Modify the reloc
	     inplace to reflect what we now know.  */
	  reloc_entry->addend = relocation;
	  reloc_entry->address += input_section->output_offset;
	  return flag;
	}
      else
	{
	  /* This is a partial relocation, but inplace, so modify the
	     reloc record a bit.

	     If we've relocated with a symbol with a section, change
	     into a ref to the section belonging to the symbol.  */

	  reloc_entry->address += input_section->output_offset;

	  /* WTF?? */
	  if (abfd->xvec->flavour == bfd_target_coff_flavour
	      && strcmp (abfd->xvec->name, "coff-Intel-little") != 0
	      && strcmp (abfd->xvec->name, "coff-Intel-big") != 0)
	    {
#if 1
	      /* For m68k-coff, the addend was being subtracted twice during
		 relocation with -r.  Removing the line below this comment
		 fixes that problem; see PR 2953.

However, Ian wrote the following, regarding removing the line below,
which explains why it is still enabled:  --djm

If you put a patch like that into BFD you need to check all the COFF
linkers.  I am fairly certain that patch will break coff-i386 (e.g.,
SCO); see coff_i386_reloc in coff-i386.c where I worked around the
problem in a different way.  There may very well be a reason that the
code works as it does.

Hmmm.  The first obvious point is that bfd_perform_relocation should
not have any tests that depend upon the flavour.  It's seem like
entirely the wrong place for such a thing.  The second obvious point
is that the current code ignores the reloc addend when producing
relocateable output for COFF.  That's peculiar.  In fact, I really
have no idea what the point of the line you want to remove is.

A typical COFF reloc subtracts the old value of the symbol and adds in
the new value to the location in the object file (if it's a pc
relative reloc it adds the difference between the symbol value and the
location).  When relocating we need to preserve that property.

BFD handles this by setting the addend to the negative of the old
value of the symbol.  Unfortunately it handles common symbols in a
non-standard way (it doesn't subtract the old value) but that's a
different story (we can't change it without losing backward
compatibility with old object files) (coff-i386 does subtract the old
value, to be compatible with existing coff-i386 targets, like SCO).

So everything works fine when not producing relocateable output.  When
we are producing relocateable output, logically we should do exactly
what we do when not producing relocateable output.  Therefore, your
patch is correct.  In fact, it should probably always just set
reloc_entry->addend to 0 for all cases, since it is, in fact, going to
add the value into the object file.  This won't hurt the COFF code,
which doesn't use the addend; I'm not sure what it will do to other
formats (the thing to check for would be whether any formats both use
the addend and set partial_inplace).

When I wanted to make coff-i386 produce relocateable output, I ran
into the problem that you are running into: I wanted to remove that
line.  Rather than risk it, I made the coff-i386 relocs use a special
function; it's coff_i386_reloc in coff-i386.c.  The function
specifically adds the addend field into the object file, knowing that
bfd_perform_relocation is not going to.  If you remove that line, then
coff-i386.c will wind up adding the addend field in twice.  It's
trivial to fix; it just needs to be done.

The problem with removing the line is just that it may break some
working code.  With BFD it's hard to be sure of anything.  The right
way to deal with this is simply to build and test at least all the
supported COFF targets.  It should be straightforward if time and disk
space consuming.  For each target:
    1) build the linker
    2) generate some executable, and link it using -r (I would
       probably use paranoia.o and link against newlib/libc.a, which
       for all the supported targets would be available in
       /usr/cygnus/progressive/H-host/target/lib/libc.a).
    3) make the change to reloc.c
    4) rebuild the linker
    5) repeat step 2
    6) if the resulting object files are the same, you have at least
       made it no worse
    7) if they are different you have to figure out which version is
       right
*/
	      relocation -= reloc_entry->addend;
#endif
	      reloc_entry->addend = 0;
	    }
	  else
	    {
	      reloc_entry->addend = relocation;
	    }
	}
    }
  else
    {
      reloc_entry->addend = 0;
    }

  /* FIXME: This overflow checking is incomplete, because the value
     might have overflowed before we get here.  For a correct check we
     need to compute the value in a size larger than bitsize, but we
     can't reasonably do that for a reloc the same size as a host
     machine word.
     FIXME: We should also do overflow checking on the result after
     adding in the value contained in the object file.  */
  if (howto->complain_on_overflow != complain_overflow_dont
      && flag == bfd_reloc_ok)
    flag = bfd_check_overflow (howto->complain_on_overflow,
			       howto->bitsize,
			       howto->rightshift,
			       bfd_arch_bits_per_address (abfd),
			       relocation);

  /*
    Either we are relocating all the way, or we don't want to apply
    the relocation to the reloc entry (probably because there isn't
    any room in the output format to describe addends to relocs)
    */

  /* The cast to bfd_vma avoids a bug in the Alpha OSF/1 C compiler
     (OSF version 1.3, compiler version 3.11).  It miscompiles the
     following program:

     struct str
     {
       unsigned int i0;
     } s = { 0 };

     int
     main ()
     {
       unsigned long x;

       x = 0x100000000;
       x <<= (unsigned long) s.i0;
       if (x == 0)
	 printf ("failed\n");
       else
	 printf ("succeeded (%lx)\n", x);
     }
     */

  relocation >>= (bfd_vma) howto->rightshift;

  /* Shift everything up to where it's going to be used */

  relocation <<= (bfd_vma) howto->bitpos;

  /* Wait for the day when all have the mask in them */

  /* What we do:
     i instruction to be left alone
     o offset within instruction
     r relocation offset to apply
     S src mask
     D dst mask
     N ~dst mask
     A part 1
     B part 2
     R result

     Do this:
     ((  i i i i i o o o o o  from bfd_get<size>
     and           S S S S S) to get the size offset we want
     +   r r r r r r r r r r) to get the final value to place
     and           D D D D D  to chop to right size
     -----------------------
     =             A A A A A
     And this:
     (   i i i i i o o o o o  from bfd_get<size>
     and N N N N N          ) get instruction
     -----------------------
     =   B B B B B

     And then:
     (   B B B B B
     or            A A A A A)
     -----------------------
     =   R R R R R R R R R R  put into bfd_put<size>
     */

#define DOIT(x) \
  x = ( (x & ~howto->dst_mask) | (((x & howto->src_mask) +  relocation) & howto->dst_mask))

  switch (howto->size)