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/* pseudo-reloc.c

   Contributed by Egor Duda  

   Modified by addition of runtime_pseudo_reloc version 2

   by Kai Tietz  

   THIS SOFTWARE IS NOT COPYRIGHTED

   This source code is offered for use in the public domain. You may

   use, modify or distribute it freely.

   This code is distributed in the hope that it will be useful but

   WITHOUT ANY WARRANTY. ALL WARRENTIES, EXPRESS OR IMPLIED ARE HEREBY

   DISCLAMED. This includes but is not limited to warrenties of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

*/

#include 

#include 

#include 

#include 

#include 

extern char __RUNTIME_PSEUDO_RELOC_LIST__;

extern char __RUNTIME_PSEUDO_RELOC_LIST_END__;

extern char _image_base__;

void _pei386_runtime_relocator (void);

/* v1 relocation is basically:

 *   *(base + .target) += .addend

 * where (base + .target) is always assumed to point

 * to a DWORD (4 bytes).

 */

typedef struct {

  uint32_t addend;

  uint32_t target;

} runtime_pseudo_reloc_item_v1;

/* v2 relocation is more complex. In effect, it is

 *    *(base + .target) += *(base + .sym) - (base + .sym)

 * with care taken in both reading, sign extension, and writing

 * because .flags may indicate that (base + .target) may point

 * to a BYTE, WORD, DWORD, or QWORD (w64).

 */

typedef struct {

  uint32_t sym;

  uint32_t target;

  uint32_t flags;

} runtime_pseudo_reloc_item_v2;

typedef struct {

  uint32_t magic1;

  uint32_t magic2;

  uint32_t version;

} runtime_pseudo_reloc_v2;

#define RP_VERSION_V1 0

#define RP_VERSION_V2 1

static void

do_pseudo_reloc (void * start, void * end, void * base)

{

  ptrdiff_t addr_imp, reldata;

  ptrdiff_t reloc_target = (ptrdiff_t) ((char *)end - (char*)start);

  runtime_pseudo_reloc_v2 *v2_hdr = (runtime_pseudo_reloc_v2 *) start;

  runtime_pseudo_reloc_item_v2 *r;

  /* A valid relocation list will contain at least one entry, and

   * one v1 data structure (the smallest one) requires two DWORDs.

   * So, if the relocation list is smaller than 8 bytes, bail.

   */

  if (reloc_target < 8)

    return;

  /* Check if this is the old pseudo relocation version.  */

  /* There are two kinds of v1 relocation lists:

   *   1) With a (v2-style) version header. In this case, the

   *      first entry in the list is a 3-DWORD structure, with

   *      value:

   *         { 0, 0, RP_VERSION_V1 }

   *      In this case, we skip to the next entry in the list,

   *      knowing that all elements after the head item can

   *      be cast to runtime_pseudo_reloc_item_v1.

   *   2) Without a (v2-style) version header. In this case, the

   *      first element in the list IS an actual v1 relocation

   *      record, which is two DWORDs.  Because there will never

   *      be a case where a v1 relocation record has both

   *      addend == 0 and target == 0, this case will not be

   *      confused with the prior one.

   * All current binutils, when generating a v1 relocation list,

   * use the second (e.g. original) form -- that is, without the

   * v2-style version header.

   */

  if (reloc_target >= 12

      && v2_hdr->magic1 == 0 && v2_hdr->magic2 == 0

      && v2_hdr->version == RP_VERSION_V1)

    {

      /* We have a list header item indicating that the rest

       * of the list contains v1 entries.  Move the pointer to

       * the first true v1 relocation record.  By definition,

       * that v1 element will not have both addend == 0 and

       * target == 0 (and thus, when interpreted as a

       * runtime_pseudo_reloc_v2, it will not have both

       * magic1 == 0 and magic2 == 0).

       */

      v2_hdr++;

    }

  if (v2_hdr->magic1 != 0 || v2_hdr->magic2 != 0)

    {

      /*************************

       * Handle v1 relocations *

       *************************/

      runtime_pseudo_reloc_item_v1 * o;

      for (o = (runtime_pseudo_reloc_item_v1 *) v2_hdr;

	   o < (runtime_pseudo_reloc_item_v1 *)end;

           o++)

	{

      uint32_t newval;

	  reloc_target = (ptrdiff_t) base + o->target;

      newval = (*((uint32_t*) reloc_target)) + o->addend;

      *(uint32_t*)reloc_target = newval;

	}

      return;

    }

  /* If we got this far, then we have relocations of version 2 or newer */

  /* Check if this is a known version.  */

  if (v2_hdr->version != RP_VERSION_V2)

    {

//      printf("  Unknown pseudo relocation protocol version %d.\n",

//             (int) v2_hdr->version);

      return;

    }

  /*************************

   * Handle v2 relocations *

   *************************/

  /* Walk over header. */

  r = (runtime_pseudo_reloc_item_v2 *) &v2_hdr[1];

  for (; r < (runtime_pseudo_reloc_item_v2 *) end; r++)

    {

      /* location where new address will be written */

      reloc_target = (ptrdiff_t) base + r->target;

      /* get sym pointer. It points either to the iat entry

       * of the referenced element, or to the stub function.

       */

      addr_imp = (ptrdiff_t) base + r->sym;

      addr_imp = *((ptrdiff_t *) addr_imp);

      /* read existing relocation value from image, casting to the

       * bitsize indicated by the 8 LSBs of flags. If the value is

       * negative, manually sign-extend to ptrdiff_t width. Raise an

       * error if the bitsize indicated by the 8 LSBs of flags is not

       * supported.

       */

      switch ((r->flags & 0xff))

        {

          case 8:

	    reldata = (ptrdiff_t) (*((unsigned char *)reloc_target));

	    if ((reldata & 0x80) != 0)

	      reldata |= ~((ptrdiff_t) 0xff);

	    break;

	  case 16:

	    reldata = (ptrdiff_t) (*((unsigned short *)reloc_target));

	    if ((reldata & 0x8000) != 0)

	      reldata |= ~((ptrdiff_t) 0xffff);

	    break;

	  case 32:

	    reldata = (ptrdiff_t) (*((unsigned int *)reloc_target));

	    break;

	  default:

	    reldata=0;

//        printf("  Unknown pseudo relocation bit size %d.\n",

//           (int) (r->flags & 0xff));

	    break;

        }

      /* Adjust the relocation value */

      reldata -= ((ptrdiff_t) base + r->sym);

      reldata += addr_imp;

      /* Write the new relocation value back to *reloc_target */

      switch ((r->flags & 0xff))

	{

         case 8:

           *(uint8_t*)reloc_target = (uint8_t)reldata;

	   break;

	 case 16:

           *(uint16_t*)reloc_target = (uint16_t)reldata;

	   break;

	 case 32:

           *(uint32_t*)reloc_target = (uint32_t)reldata;

	   break;

	}

     }

}

void

_pei386_runtime_relocator (void)

{

  static int was_init = 0;

  if (was_init)

    return;

  ++was_init;

  do_pseudo_reloc (&__RUNTIME_PSEUDO_RELOC_LIST__,

		   &__RUNTIME_PSEUDO_RELOC_LIST_END__,

           &_image_base__);

}