dl-machine.c

Glibc 2.3.2源代码(解压后有100多M)

/* Machine-dependent ELF dynamic relocation functions.  PowerPC version.
   Copyright (C) 1995-2001, 2002 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <unistd.h>
#include <string.h>
#include <sys/param.h>
#include <link.h>
#include <ldsodefs.h>
#include <elf/dynamic-link.h>
#include <dl-machine.h>
#include <stdio-common/_itoa.h>

/* Because ld.so is now versioned, these functions can be in their own file;
   no relocations need to be done to call them.
   Of course, if ld.so is not versioned...  */
#if defined SHARED && !(DO_VERSIONING - 0)
#error This will not work with versioning turned off, sorry.
#endif


/* Stuff for the PLT.  */
#define PLT_INITIAL_ENTRY_WORDS 18
#define PLT_LONGBRANCH_ENTRY_WORDS 0
#define PLT_TRAMPOLINE_ENTRY_WORDS 6
#define PLT_DOUBLE_SIZE (1<<13)
#define PLT_ENTRY_START_WORDS(entry_number) \
  (PLT_INITIAL_ENTRY_WORDS + (entry_number)*2				\
   + ((entry_number) > PLT_DOUBLE_SIZE					\
      ? ((entry_number) - PLT_DOUBLE_SIZE)*2				\
      : 0))
#define PLT_DATA_START_WORDS(num_entries) PLT_ENTRY_START_WORDS(num_entries)

/* Macros to build PowerPC opcode words.  */
#define OPCODE_ADDI(rd,ra,simm) \
  (0x38000000 | (rd) << 21 | (ra) << 16 | ((simm) & 0xffff))
#define OPCODE_ADDIS(rd,ra,simm) \
  (0x3c000000 | (rd) << 21 | (ra) << 16 | ((simm) & 0xffff))
#define OPCODE_ADD(rd,ra,rb) \
  (0x7c000214 | (rd) << 21 | (ra) << 16 | (rb) << 11)
#define OPCODE_B(target) (0x48000000 | ((target) & 0x03fffffc))
#define OPCODE_BA(target) (0x48000002 | ((target) & 0x03fffffc))
#define OPCODE_BCTR() 0x4e800420
#define OPCODE_LWZ(rd,d,ra) \
  (0x80000000 | (rd) << 21 | (ra) << 16 | ((d) & 0xffff))
#define OPCODE_LWZU(rd,d,ra) \
  (0x84000000 | (rd) << 21 | (ra) << 16 | ((d) & 0xffff))
#define OPCODE_MTCTR(rd) (0x7C0903A6 | (rd) << 21)
#define OPCODE_RLWINM(ra,rs,sh,mb,me) \
  (0x54000000 | (rs) << 21 | (ra) << 16 | (sh) << 11 | (mb) << 6 | (me) << 1)

#define OPCODE_LI(rd,simm)    OPCODE_ADDI(rd,0,simm)
#define OPCODE_ADDIS_HI(rd,ra,value) \
  OPCODE_ADDIS(rd,ra,((value) + 0x8000) >> 16)
#define OPCODE_LIS_HI(rd,value) OPCODE_ADDIS_HI(rd,0,value)
#define OPCODE_SLWI(ra,rs,sh) OPCODE_RLWINM(ra,rs,sh,0,31-sh)


#define PPC_DCBST(where) asm volatile ("dcbst 0,%0" : : "r"(where) : "memory")
#define PPC_SYNC asm volatile ("sync" : : : "memory")
#define PPC_ISYNC asm volatile ("sync; isync" : : : "memory")
#define PPC_ICBI(where) asm volatile ("icbi 0,%0" : : "r"(where) : "memory")
#define PPC_DIE asm volatile ("tweq 0,0")

/* Use this when you've modified some code, but it won't be in the
   instruction fetch queue (or when it doesn't matter if it is). */
#define MODIFIED_CODE_NOQUEUE(where) \
     do { PPC_DCBST(where); PPC_SYNC; PPC_ICBI(where); } while (0)
/* Use this when it might be in the instruction queue. */
#define MODIFIED_CODE(where) \
     do { PPC_DCBST(where); PPC_SYNC; PPC_ICBI(where); PPC_ISYNC; } while (0)


/* The idea here is that to conform to the ABI, we are supposed to try
   to load dynamic objects between 0x10000 (we actually use 0x40000 as
   the lower bound, to increase the chance of a memory reference from
   a null pointer giving a segfault) and the program's load address;
   this may allow us to use a branch instruction in the PLT rather
   than a computed jump.  The address is only used as a preference for
   mmap, so if we get it wrong the worst that happens is that it gets
   mapped somewhere else.  */

ElfW(Addr)
__elf_preferred_address(struct link_map *loader, size_t maplength,
			ElfW(Addr) mapstartpref)
{
  ElfW(Addr) low, high;
  struct link_map *l;

  /* If the object has a preference, load it there!  */
  if (mapstartpref != 0)
    return mapstartpref;

  /* Otherwise, quickly look for a suitable gap between 0x3FFFF and
     0x70000000.  0x3FFFF is so that references off NULL pointers will
     cause a segfault, 0x70000000 is just paranoia (it should always
     be superceded by the program's load address).  */
  low =  0x0003FFFF;
  high = 0x70000000;
  for (l = GL(dl_loaded); l; l = l->l_next)
    {
      ElfW(Addr) mapstart, mapend;
      mapstart = l->l_map_start & ~(GL(dl_pagesize) - 1);
      mapend = l->l_map_end | (GL(dl_pagesize) - 1);
      assert (mapend > mapstart);

      /* Prefer gaps below the main executable, note that l ==
	 _dl_loaded does not work for static binaries loading
	 e.g. libnss_*.so.  */
      if ((mapend >= high || l->l_type == lt_executable)
	  && high >= mapstart)
	high = mapstart;
      else if (mapend >= low && low >= mapstart)
	low = mapend;
      else if (high >= mapend && mapstart >= low)
	{
	  if (high - mapend >= mapstart - low)
	    low = mapend;
	  else
	    high = mapstart;
	}
    }

  high -= 0x10000; /* Allow some room between objects.  */
  maplength = (maplength | (GL(dl_pagesize) - 1)) + 1;
  if (high <= low || high - low < maplength )
    return 0;
  return high - maplength;  /* Both high and maplength are page-aligned.  */
}

/* Set up the loaded object described by L so its unrelocated PLT
   entries will jump to the on-demand fixup code in dl-runtime.c.
   Also install a small trampoline to be used by entries that have
   been relocated to an address too far away for a single branch.  */

/* There are many kinds of PLT entries:

   (1)	A direct jump to the actual routine, either a relative or
	absolute branch.  These are set up in __elf_machine_fixup_plt.

   (2)	Short lazy entries.  These cover the first 8192 slots in
        the PLT, and look like (where 'index' goes from 0 to 8191):

	li %r11, index*4
	b  &plt[PLT_TRAMPOLINE_ENTRY_WORDS+1]

   (3)	Short indirect jumps.  These replace (2) when a direct jump
	wouldn't reach.  They look the same except that the branch
	is 'b &plt[PLT_LONGBRANCH_ENTRY_WORDS]'.

   (4)  Long lazy entries.  These cover the slots when a short entry
	won't fit ('index*4' overflows its field), and look like:

	lis %r11, %hi(index*4 + &plt[PLT_DATA_START_WORDS])
	lwzu %r12, %r11, %lo(index*4 + &plt[PLT_DATA_START_WORDS])
	b  &plt[PLT_TRAMPOLINE_ENTRY_WORDS]
	bctr

   (5)	Long indirect jumps.  These replace (4) when a direct jump
	wouldn't reach.  They look like:

	lis %r11, %hi(index*4 + &plt[PLT_DATA_START_WORDS])
	lwz %r12, %r11, %lo(index*4 + &plt[PLT_DATA_START_WORDS])
	mtctr %r12
	bctr

   (6) Long direct jumps.  These are used when thread-safety is not
       required.  They look like:

       lis %r12, %hi(finaladdr)
       addi %r12, %r12, %lo(finaladdr)
       mtctr %r12
       bctr


   The lazy entries, (2) and (4), are set up here in
   __elf_machine_runtime_setup.  (1), (3), and (5) are set up in
   __elf_machine_fixup_plt.  (1), (3), and (6) can also be constructed
   in __process_machine_rela.

   The reason for the somewhat strange construction of the long
   entries, (4) and (5), is that we need to ensure thread-safety.  For
   (1) and (3), this is obvious because only one instruction is
   changed and the PPC architecture guarantees that aligned stores are
   atomic.  For (5), this is more tricky.  When changing (4) to (5),
   the `b' instruction is first changed to to `mtctr'; this is safe
   and is why the `lwzu' instruction is not just a simple `addi'.
   Once this is done, and is visible to all processors, the `lwzu' can
   safely be changed to a `lwz'.  */
int
__elf_machine_runtime_setup (struct link_map *map, int lazy, int profile)
{
  if (map->l_info[DT_JMPREL])
    {
      Elf32_Word i;
      Elf32_Word *plt = (Elf32_Word *) D_PTR (map, l_info[DT_PLTGOT]);
      Elf32_Word num_plt_entries = (map->l_info[DT_PLTRELSZ]->d_un.d_val
				    / sizeof (Elf32_Rela));
      Elf32_Word rel_offset_words = PLT_DATA_START_WORDS (num_plt_entries);
      Elf32_Word data_words = (Elf32_Word) (plt + rel_offset_words);
      Elf32_Word size_modified;

      extern void _dl_runtime_resolve (void);
      extern void _dl_prof_resolve (void);

      /* Convert the index in r11 into an actual address, and get the
	 word at that address.  */
      plt[PLT_LONGBRANCH_ENTRY_WORDS] = OPCODE_ADDIS_HI (11, 11, data_words);
      plt[PLT_LONGBRANCH_ENTRY_WORDS + 1] = OPCODE_LWZ (11, data_words, 11);

      /* Call the procedure at that address.  */
      plt[PLT_LONGBRANCH_ENTRY_WORDS + 2] = OPCODE_MTCTR (11);
      plt[PLT_LONGBRANCH_ENTRY_WORDS + 3] = OPCODE_BCTR ();

      if (lazy)
	{
	  Elf32_Word *tramp = plt + PLT_TRAMPOLINE_ENTRY_WORDS;
	  Elf32_Word dlrr = (Elf32_Word)(profile
					 ? _dl_prof_resolve
					 : _dl_runtime_resolve);
	  Elf32_Word offset;

	  if (profile && _dl_name_match_p (GL(dl_profile), map))
	    /* This is the object we are looking for.  Say that we really
	       want profiling and the timers are started.  */
	    GL(dl_profile_map) = map;

	  /* For the long entries, subtract off data_words.  */
	  tramp[0] = OPCODE_ADDIS_HI (11, 11, -data_words);
	  tramp[1] = OPCODE_ADDI (11, 11, -data_words);

	  /* Multiply index of entry by 3 (in r11).  */
	  tramp[2] = OPCODE_SLWI (12, 11, 1);
	  tramp[3] = OPCODE_ADD (11, 12, 11);
	  if (dlrr <= 0x01fffffc || dlrr >= 0xfe000000)
	    {
	      /* Load address of link map in r12.  */
	      tramp[4] = OPCODE_LI (12, (Elf32_Word) map);
	      tramp[5] = OPCODE_ADDIS_HI (12, 12, (Elf32_Word) map);

	      /* Call _dl_runtime_resolve.  */
	      tramp[6] = OPCODE_BA (dlrr);
	    }
	  else
	    {
	      /* Get address of _dl_runtime_resolve in CTR.  */
	      tramp[4] = OPCODE_LI (12, dlrr);
	      tramp[5] = OPCODE_ADDIS_HI (12, 12, dlrr);
	      tramp[6] = OPCODE_MTCTR (12);

	      /* Load address of link map in r12.  */
	      tramp[7] = OPCODE_LI (12, (Elf32_Word) map);
	      tramp[8] = OPCODE_ADDIS_HI (12, 12, (Elf32_Word) map);

	      /* Call _dl_runtime_resolve.  */
	      tramp[9] = OPCODE_BCTR ();
	    }

	  /* Set up the lazy PLT entries.  */
	  offset = PLT_INITIAL_ENTRY_WORDS;
	  i = 0;