include/aout/sun4.h

   1 /* SPARC-specific values for a.out files
   2
   3    Copyright 2001, 2009 Free Software Foundation, Inc.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, write to the Free Software
  17    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.  */
  18
  19 /* Some systems, e.g., AIX, may have defined this in header files already
  20    included.  */
  21 #undef  TARGET_PAGE_SIZE
  22 #define TARGET_PAGE_SIZE        0x2000          /* 8K.  aka NBPG in <sys/param.h> */
  23 /* Note that some SPARCs have 4K pages, some 8K, some others.  */
  24
  25 #define SEG_SIZE_SPARC  TARGET_PAGE_SIZE
  26 #define SEG_SIZE_SUN3   0x20000         /* Resolution of r/w protection hw */
  27
  28 #define TEXT_START_ADDR TARGET_PAGE_SIZE        /* Location 0 is not accessible */
  29 #define N_HEADER_IN_TEXT(x) 1
  30
  31 /* Non-default definitions of the accessor macros... */
  32
  33 /* Segment size varies on Sun-3 versus Sun-4.  */
  34
  35 #define N_SEGSIZE(x)    (N_MACHTYPE(x) == M_SPARC?      SEG_SIZE_SPARC: \
  36                          N_MACHTYPE(x) == M_68020?      SEG_SIZE_SUN3:  \
  37                         /* Guess? */                    TARGET_PAGE_SIZE)
  38
  39 /* Virtual Address of text segment from the a.out file.  For OMAGIC,
  40    (almost always "unlinked .o's" these days), should be zero.
  41    Sun added a kludge so that shared libraries linked ZMAGIC get
  42    an address of zero if a_entry (!!!) is lower than the otherwise
  43    expected text address.  These kludges have gotta go!
  44    For linked files, should reflect reality if we know it.  */
  45
  46 #define N_SHARED_LIB(x) ((x).a_entry < TEXT_START_ADDR \
  47                          && (x).a_text >= EXEC_BYTES_SIZE)
  48
  49 /* This differs from the version in aout64.h (which we override by defining
  50    it here) only for NMAGIC (we return TEXT_START_ADDR+EXEC_BYTES_SIZE;
  51    they return 0).  */
  52
  53 #define N_TXTADDR(x) \
  54     (N_MAGIC(x)==OMAGIC? 0 \
  55      : (N_MAGIC(x) == ZMAGIC && (x).a_entry < TEXT_START_ADDR)? 0 \
  56      : TEXT_START_ADDR+EXEC_BYTES_SIZE)
  57
  58 /* When a file is linked against a shared library on SunOS 4, the
  59    dynamic bit in the exec header is set, and the first symbol in the
  60    symbol table is __DYNAMIC.  Its value is the address of the
  61    following structure.  */
  62
  63 struct external_sun4_dynamic
  64 {
  65   /* The version number of the structure.  SunOS 4.1.x creates files
  66      with version number 3, which is what this structure is based on.
  67      According to gdb, version 2 is similar.  I believe that version 2
  68      used a different type of procedure linkage table, and there may
  69      have been other differences.  */
  70   bfd_byte ld_version[4];
  71   /* The virtual address of a 28 byte structure used in debugging.
  72      The contents are filled in at run time by ld.so.  */
  73   bfd_byte ldd[4];
  74   /* The virtual address of another structure with information about
  75      how to relocate the executable at run time.  */
  76   bfd_byte ld[4];
  77 };
  78
  79 /* The size of the debugging structure pointed to by the debugger
  80    field of __DYNAMIC.  */
  81 #define EXTERNAL_SUN4_DYNAMIC_DEBUGGER_SIZE (24)
  82
  83 /* The structure pointed to by the linker field of __DYNAMIC.  As far
  84    as I can tell, most of the addresses in this structure are offsets
  85    within the file, but some are actually virtual addresses.  */
  86
  87 struct internal_sun4_dynamic_link
  88 {
  89   /* Linked list of loaded objects.  This is filled in at runtime by
  90      ld.so and probably by dlopen.  */
  91   unsigned long ld_loaded;
  92
  93   /* The address of the list of names of shared objects which must be
  94      included at runtime.  Each entry in the list is 16 bytes: the 4
  95      byte address of the string naming the object (e.g., for -lc this
  96      is "c"); 4 bytes of flags--the high bit is whether to search for
  97      the object using the library path; the 2 byte major version
  98      number; the 2 byte minor version number; the 4 byte address of
  99      the next entry in the list (zero if this is the last entry).  The
 100      version numbers seem to only be non-zero when doing library
 101      searching.  */
 102   unsigned long ld_need;
 103
 104   /* The address of the path to search for the shared objects which
 105      must be included.  This points to a string in PATH format which
 106      is generated from the -L arguments to the linker.  According to
 107      the man page, ld.so implicitly adds ${LD_LIBRARY_PATH} to the
 108      beginning of this string and /lib:/usr/lib:/usr/local/lib to the
 109      end.  The string is terminated by a null byte.  This field is
 110      zero if there is no additional path.  */
 111   unsigned long ld_rules;
 112
 113   /* The address of the global offset table.  This appears to be a
 114      virtual address, not a file offset.  The first entry in the
 115      global offset table seems to be the virtual address of the
 116      sun4_dynamic structure (the same value as the __DYNAMIC symbol).
 117      The global offset table is used for PIC code to hold the
 118      addresses of variables.  A dynamically linked file which does not
 119      itself contain PIC code has a four byte global offset table.  */
 120   unsigned long ld_got;
 121
 122   /* The address of the procedure linkage table.  This appears to be a
 123      virtual address, not a file offset.
 124
 125      On a SPARC, the table is composed of 12 byte entries, each of
 126      which consists of three instructions.  The first entry is
 127          sethi %hi(0),%g1
 128          jmp %g1
 129          nop
 130      These instructions are changed by ld.so into a jump directly into
 131      ld.so itself.  Each subsequent entry is
 132          save %sp, -96, %sp
 133          call <address of first entry in procedure linkage table>
 134          <reloc_number | 0x01000000>
 135      The reloc_number is the number of the reloc to use to resolve
 136      this entry.  The reloc will be a JMP_SLOT reloc against some
 137      symbol that is not defined in this object file but should be
 138      defined in a shared object (if it is not, ld.so will report a
 139      runtime error and exit).  The constant 0x010000000 turns the
 140      reloc number into a sethi of %g0, which does nothing since %g0 is
 141      hardwired to zero.
 142
 143      When one of these entries is executed, it winds up calling into
 144      ld.so.  ld.so looks at the reloc number, available via the return
 145      address, to determine which entry this is.  It then looks at the
 146      reloc and patches up the entry in the table into a sethi and jmp
 147      to the real address followed by a nop.  This means that the reloc
 148      lookup only has to happen once, and it also means that the
 149      relocation only needs to be done if the function is actually
 150      called.  The relocation is expensive because ld.so must look up
 151      the symbol by name.
 152
 153      The size of the procedure linkage table is given by the ld_plt_sz
 154      field.  */
 155   unsigned long ld_plt;
 156
 157   /* The address of the relocs.  These are in the same format as
 158      ordinary relocs.  Symbol index numbers refer to the symbols
 159      pointed to by ld_stab.  I think the only way to determine the
 160      number of relocs is to assume that all the bytes from ld_rel to
 161      ld_hash contain reloc entries.  */
 162   unsigned long ld_rel;
 163
 164   /* The address of a hash table of symbols.  The hash table has
 165      roughly the same number of entries as there are dynamic symbols;
 166      I think the only way to get the exact size is to assume that
 167      every byte from ld_hash to ld_stab is devoted to the hash table.
 168
 169      Each entry in the hash table is eight bytes.  The first four
 170      bytes are a symbol index into the dynamic symbols.  The second
 171      four bytes are the index of the next hash table entry in the
 172      bucket.  The ld_buckets field gives the number of buckets, say B.
 173      The first B entries in the hash table each start a bucket which
 174      is chained through the second four bytes of each entry.  A value
 175      of zero ends the chain.
 176
 177      The hash function is simply
 178          h = 0;
 179          while (*string != '\0')
 180            h = (h << 1) + *string++;
 181          h &= 0x7fffffff;
 182
 183      To look up a symbol, compute the hash value of the name.  Take
 184      the modulos of hash value and the number of buckets.  Start at
 185      that entry in the hash table.  See if the symbol (from the first
 186      four bytes of the hash table entry) has the name you are looking
 187      for.  If not, use the chain field (the second four bytes of the
 188      hash table entry) to move on to the next entry in this bucket.
 189      If the chain field is zero you have reached the end of the
 190      bucket, and the symbol is not in the hash table.  */
 191   unsigned long ld_hash;
 192
 193   /* The address of the symbol table.  This is a list of
 194      external_nlist structures.  The string indices are relative to
 195      the ld_symbols field.  I think the only way to determine the
 196      number of symbols is to assume that all the bytes between ld_stab
 197      and ld_symbols are external_nlist structures.  */
 198   unsigned long ld_stab;
 199
 200   /* I don't know what this is for.  It seems to always be zero.  */
 201   unsigned long ld_stab_hash;
 202
 203   /* The number of buckets in the hash table.  */
 204   unsigned long ld_buckets;
 205
 206   /* The address of the symbol string table.  The first string in this
 207      string table need not be the empty string.  */
 208   unsigned long ld_symbols;
 209
 210   /* The size in bytes of the symbol string table.  */
 211   unsigned long ld_symb_size;
 212
 213   /* The size in bytes of the text segment.  */
 214   unsigned long ld_text;
 215
 216   /* The size in bytes of the procedure linkage table.  */
 217   unsigned long ld_plt_sz;
 218 };
 219
 220 /* The external form of the structure.  */
 221
 222 struct external_sun4_dynamic_link
 223 {
 224   bfd_byte ld_loaded[4];
 225   bfd_byte ld_need[4];
 226   bfd_byte ld_rules[4];
 227   bfd_byte ld_got[4];
 228   bfd_byte ld_plt[4];
 229   bfd_byte ld_rel[4];
 230   bfd_byte ld_hash[4];
 231   bfd_byte ld_stab[4];
 232   bfd_byte ld_stab_hash[4];
 233   bfd_byte ld_buckets[4];
 234   bfd_byte ld_symbols[4];
 235   bfd_byte ld_symb_size[4];
 236   bfd_byte ld_text[4];
 237   bfd_byte ld_plt_sz[4];
 238 };