include/aout/sun4.h

   1 /* SPARC-specific values for a.out files
   2
   3    Copyright 2001 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, 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 /* This differs from the version in aout64.h (which we override by defining
  47    it here) only for NMAGIC (we return TEXT_START_ADDR+EXEC_BYTES_SIZE;
  48    they return 0).  */
  49
  50 #define N_TXTADDR(x) \
  51     (N_MAGIC(x)==OMAGIC? 0 \
  52      : (N_MAGIC(x) == ZMAGIC && (x).a_entry < TEXT_START_ADDR)? 0 \
  53      : TEXT_START_ADDR+EXEC_BYTES_SIZE)
  54
  55 /* When a file is linked against a shared library on SunOS 4, the
  56    dynamic bit in the exec header is set, and the first symbol in the
  57    symbol table is __DYNAMIC.  Its value is the address of the
  58    following structure.  */
  59
  60 struct external_sun4_dynamic
  61 {
  62   /* The version number of the structure.  SunOS 4.1.x creates files
  63      with version number 3, which is what this structure is based on.
  64      According to gdb, version 2 is similar.  I believe that version 2
  65      used a different type of procedure linkage table, and there may
  66      have been other differences.  */
  67   bfd_byte ld_version[4];
  68   /* The virtual address of a 28 byte structure used in debugging.
  69      The contents are filled in at run time by ld.so.  */
  70   bfd_byte ldd[4];
  71   /* The virtual address of another structure with information about
  72      how to relocate the executable at run time.  */
  73   bfd_byte ld[4];
  74 };
  75
  76 /* The size of the debugging structure pointed to by the debugger
  77    field of __DYNAMIC.  */
  78 #define EXTERNAL_SUN4_DYNAMIC_DEBUGGER_SIZE (24)
  79
  80 /* The structure pointed to by the linker field of __DYNAMIC.  As far
  81    as I can tell, most of the addresses in this structure are offsets
  82    within the file, but some are actually virtual addresses.  */
  83
  84 struct internal_sun4_dynamic_link
  85 {
  86   /* Linked list of loaded objects.  This is filled in at runtime by
  87      ld.so and probably by dlopen.  */
  88   unsigned long ld_loaded;
  89
  90   /* The address of the list of names of shared objects which must be
  91      included at runtime.  Each entry in the list is 16 bytes: the 4
  92      byte address of the string naming the object (e.g., for -lc this
  93      is "c"); 4 bytes of flags--the high bit is whether to search for
  94      the object using the library path; the 2 byte major version
  95      number; the 2 byte minor version number; the 4 byte address of
  96      the next entry in the list (zero if this is the last entry).  The
  97      version numbers seem to only be non-zero when doing library
  98      searching.  */
  99   unsigned long ld_need;
 100
 101   /* The address of the path to search for the shared objects which
 102      must be included.  This points to a string in PATH format which
 103      is generated from the -L arguments to the linker.  According to
 104      the man page, ld.so implicitly adds ${LD_LIBRARY_PATH} to the
 105      beginning of this string and /lib:/usr/lib:/usr/local/lib to the
 106      end.  The string is terminated by a null byte.  This field is
 107      zero if there is no additional path.  */
 108   unsigned long ld_rules;
 109
 110   /* The address of the global offset table.  This appears to be a
 111      virtual address, not a file offset.  The first entry in the
 112      global offset table seems to be the virtual address of the
 113      sun4_dynamic structure (the same value as the __DYNAMIC symbol).
 114      The global offset table is used for PIC code to hold the
 115      addresses of variables.  A dynamically linked file which does not
 116      itself contain PIC code has a four byte global offset table.  */
 117   unsigned long ld_got;
 118
 119   /* The address of the procedure linkage table.  This appears to be a
 120      virtual address, not a file offset.
 121
 122      On a SPARC, the table is composed of 12 byte entries, each of
 123      which consists of three instructions.  The first entry is
 124          sethi %hi(0),%g1
 125          jmp %g1
 126          nop
 127      These instructions are changed by ld.so into a jump directly into
 128      ld.so itself.  Each subsequent entry is
 129          save %sp, -96, %sp
 130          call <address of first entry in procedure linkage table>
 131          <reloc_number | 0x01000000>
 132      The reloc_number is the number of the reloc to use to resolve
 133      this entry.  The reloc will be a JMP_SLOT reloc against some
 134      symbol that is not defined in this object file but should be
 135      defined in a shared object (if it is not, ld.so will report a
 136      runtime error and exit).  The constant 0x010000000 turns the
 137      reloc number into a sethi of %g0, which does nothing since %g0 is
 138      hardwired to zero.
 139
 140      When one of these entries is executed, it winds up calling into
 141      ld.so.  ld.so looks at the reloc number, available via the return
 142      address, to determine which entry this is.  It then looks at the
 143      reloc and patches up the entry in the table into a sethi and jmp
 144      to the real address followed by a nop.  This means that the reloc
 145      lookup only has to happen once, and it also means that the
 146      relocation only needs to be done if the function is actually
 147      called.  The relocation is expensive because ld.so must look up
 148      the symbol by name.
 149
 150      The size of the procedure linkage table is given by the ld_plt_sz
 151      field.  */
 152   unsigned long ld_plt;
 153
 154   /* The address of the relocs.  These are in the same format as
 155      ordinary relocs.  Symbol index numbers refer to the symbols
 156      pointed to by ld_stab.  I think the only way to determine the
 157      number of relocs is to assume that all the bytes from ld_rel to
 158      ld_hash contain reloc entries.  */
 159   unsigned long ld_rel;
 160
 161   /* The address of a hash table of symbols.  The hash table has
 162      roughly the same number of entries as there are dynamic symbols;
 163      I think the only way to get the exact size is to assume that
 164      every byte from ld_hash to ld_stab is devoted to the hash table.
 165
 166      Each entry in the hash table is eight bytes.  The first four
 167      bytes are a symbol index into the dynamic symbols.  The second
 168      four bytes are the index of the next hash table entry in the
 169      bucket.  The ld_buckets field gives the number of buckets, say B.
 170      The first B entries in the hash table each start a bucket which
 171      is chained through the second four bytes of each entry.  A value
 172      of zero ends the chain.
 173
 174      The hash function is simply
 175          h = 0;
 176          while (*string != '\0')
 177            h = (h << 1) + *string++;
 178          h &= 0x7fffffff;
 179
 180      To look up a symbol, compute the hash value of the name.  Take
 181      the modulos of hash value and the number of buckets.  Start at
 182      that entry in the hash table.  See if the symbol (from the first
 183      four bytes of the hash table entry) has the name you are looking
 184      for.  If not, use the chain field (the second four bytes of the
 185      hash table entry) to move on to the next entry in this bucket.
 186      If the chain field is zero you have reached the end of the
 187      bucket, and the symbol is not in the hash table.  */
 188   unsigned long ld_hash;
 189
 190   /* The address of the symbol table.  This is a list of
 191      external_nlist structures.  The string indices are relative to
 192      the ld_symbols field.  I think the only way to determine the
 193      number of symbols is to assume that all the bytes between ld_stab
 194      and ld_symbols are external_nlist structures.  */
 195   unsigned long ld_stab;
 196
 197   /* I don't know what this is for.  It seems to always be zero.  */
 198   unsigned long ld_stab_hash;
 199
 200   /* The number of buckets in the hash table.  */
 201   unsigned long ld_buckets;
 202
 203   /* The address of the symbol string table.  The first string in this
 204      string table need not be the empty string.  */
 205   unsigned long ld_symbols;
 206
 207   /* The size in bytes of the symbol string table.  */
 208   unsigned long ld_symb_size;
 209
 210   /* The size in bytes of the text segment.  */
 211   unsigned long ld_text;
 212
 213   /* The size in bytes of the procedure linkage table.  */
 214   unsigned long ld_plt_sz;
 215 };
 216
 217 /* The external form of the structure.  */
 218
 219 struct external_sun4_dynamic_link
 220 {
 221   bfd_byte ld_loaded[4];
 222   bfd_byte ld_need[4];
 223   bfd_byte ld_rules[4];
 224   bfd_byte ld_got[4];
 225   bfd_byte ld_plt[4];
 226   bfd_byte ld_rel[4];
 227   bfd_byte ld_hash[4];
 228   bfd_byte ld_stab[4];
 229   bfd_byte ld_stab_hash[4];
 230   bfd_byte ld_buckets[4];
 231   bfd_byte ld_symbols[4];
 232   bfd_byte ld_symb_size[4];
 233   bfd_byte ld_text[4];
 234   bfd_byte ld_plt_sz[4];
 235 };