include/aout/sun4.h

   1 /* SPARC-specific values for a.out files
   2
   3    Copyright (C) 2001-2024 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 3 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,
  18    MA 02110-1301, USA.  */
  19
  20 /* Some systems, e.g., AIX, may have defined this in header files already
  21    included.  */
  22 #undef  TARGET_PAGE_SIZE
  23 #define TARGET_PAGE_SIZE        0x2000          /* 8K.  aka NBPG in <sys/param.h> */
  24 /* Note that some SPARCs have 4K pages, some 8K, some others.  */
  25
  26 #define SEG_SIZE_SPARC  TARGET_PAGE_SIZE
  27 #define SEG_SIZE_SUN3   0x20000         /* Resolution of r/w protection hw */
  28
  29 #define TEXT_START_ADDR TARGET_PAGE_SIZE        /* Location 0 is not accessible */
  30 #define N_HEADER_IN_TEXT(x) 1
  31
  32 /* Non-default definitions of the accessor macros... */
  33
  34 /* Segment size varies on Sun-3 versus Sun-4.  */
  35
  36 #define N_SEGSIZE(x)    (N_MACHTYPE(x) == M_SPARC?      SEG_SIZE_SPARC: \
  37                          N_MACHTYPE(x) == M_68020?      SEG_SIZE_SUN3:  \
  38                         /* Guess? */                    TARGET_PAGE_SIZE)
  39
  40 /* Virtual Address of text segment from the a.out file.  For OMAGIC,
  41    (almost always "unlinked .o's" these days), should be zero.
  42    Sun added a kludge so that shared libraries linked ZMAGIC get
  43    an address of zero if a_entry (!!!) is lower than the otherwise
  44    expected text address.  These kludges have gotta go!
  45    For linked files, should reflect reality if we know it.  */
  46
  47 #define N_SHARED_LIB(x) ((x)->a_entry < TEXT_START_ADDR \
  48                          && (x)->a_text >= EXEC_BYTES_SIZE)
  49
  50 /* This differs from the version in aout64.h (which we override by defining
  51    it here) only for NMAGIC (we return TEXT_START_ADDR+EXEC_BYTES_SIZE;
  52    they return 0).  */
  53
  54 #define N_TXTADDR(x) \
  55     (N_MAGIC(x)==OMAGIC? 0 \
  56      : (N_MAGIC(x) == ZMAGIC && (x)->a_entry < TEXT_START_ADDR)? 0 \
  57      : TEXT_START_ADDR+EXEC_BYTES_SIZE)
  58
  59 /* When a file is linked against a shared library on SunOS 4, the
  60    dynamic bit in the exec header is set, and the first symbol in the
  61    symbol table is __DYNAMIC.  Its value is the address of the
  62    following structure.  */
  63
  64 struct external_sun4_dynamic
  65 {
  66   /* The version number of the structure.  SunOS 4.1.x creates files
  67      with version number 3, which is what this structure is based on.
  68      According to gdb, version 2 is similar.  I believe that version 2
  69      used a different type of procedure linkage table, and there may
  70      have been other differences.  */
  71   bfd_byte ld_version[4];
  72   /* The virtual address of a 28 byte structure used in debugging.
  73      The contents are filled in at run time by ld.so.  */
  74   bfd_byte ldd[4];
  75   /* The virtual address of another structure with information about
  76      how to relocate the executable at run time.  */
  77   bfd_byte ld[4];
  78 };
  79
  80 /* The size of the debugging structure pointed to by the debugger
  81    field of __DYNAMIC.  */
  82 #define EXTERNAL_SUN4_DYNAMIC_DEBUGGER_SIZE (24)
  83
  84 /* The structure pointed to by the linker field of __DYNAMIC.  As far
  85    as I can tell, most of the addresses in this structure are offsets
  86    within the file, but some are actually virtual addresses.  */
  87
  88 struct internal_sun4_dynamic_link
  89 {
  90   /* Linked list of loaded objects.  This is filled in at runtime by
  91      ld.so and probably by dlopen.  */
  92   unsigned long ld_loaded;
  93
  94   /* The address of the list of names of shared objects which must be
  95      included at runtime.  Each entry in the list is 16 bytes: the 4
  96      byte address of the string naming the object (e.g., for -lc this
  97      is "c"); 4 bytes of flags--the high bit is whether to search for
  98      the object using the library path; the 2 byte major version
  99      number; the 2 byte minor version number; the 4 byte address of
 100      the next entry in the list (zero if this is the last entry).  The
 101      version numbers seem to only be non-zero when doing library
 102      searching.  */
 103   unsigned long ld_need;
 104
 105   /* The address of the path to search for the shared objects which
 106      must be included.  This points to a string in PATH format which
 107      is generated from the -L arguments to the linker.  According to
 108      the man page, ld.so implicitly adds ${LD_LIBRARY_PATH} to the
 109      beginning of this string and /lib:/usr/lib:/usr/local/lib to the
 110      end.  The string is terminated by a null byte.  This field is
 111      zero if there is no additional path.  */
 112   unsigned long ld_rules;
 113
 114   /* The address of the global offset table.  This appears to be a
 115      virtual address, not a file offset.  The first entry in the
 116      global offset table seems to be the virtual address of the
 117      sun4_dynamic structure (the same value as the __DYNAMIC symbol).
 118      The global offset table is used for PIC code to hold the
 119      addresses of variables.  A dynamically linked file which does not
 120      itself contain PIC code has a four byte global offset table.  */
 121   unsigned long ld_got;
 122
 123   /* The address of the procedure linkage table.  This appears to be a
 124      virtual address, not a file offset.
 125
 126      On a SPARC, the table is composed of 12 byte entries, each of
 127      which consists of three instructions.  The first entry is
 128          sethi %hi(0),%g1
 129          jmp %g1
 130          nop
 131      These instructions are changed by ld.so into a jump directly into
 132      ld.so itself.  Each subsequent entry is
 133          save %sp, -96, %sp
 134          call <address of first entry in procedure linkage table>
 135          <reloc_number | 0x01000000>
 136      The reloc_number is the number of the reloc to use to resolve
 137      this entry.  The reloc will be a JMP_SLOT reloc against some
 138      symbol that is not defined in this object file but should be
 139      defined in a shared object (if it is not, ld.so will report a
 140      runtime error and exit).  The constant 0x010000000 turns the
 141      reloc number into a sethi of %g0, which does nothing since %g0 is
 142      hardwired to zero.
 143
 144      When one of these entries is executed, it winds up calling into
 145      ld.so.  ld.so looks at the reloc number, available via the return
 146      address, to determine which entry this is.  It then looks at the
 147      reloc and patches up the entry in the table into a sethi and jmp
 148      to the real address followed by a nop.  This means that the reloc
 149      lookup only has to happen once, and it also means that the
 150      relocation only needs to be done if the function is actually
 151      called.  The relocation is expensive because ld.so must look up
 152      the symbol by name.
 153
 154      The size of the procedure linkage table is given by the ld_plt_sz
 155      field.  */
 156   unsigned long ld_plt;
 157
 158   /* The address of the relocs.  These are in the same format as
 159      ordinary relocs.  Symbol index numbers refer to the symbols
 160      pointed to by ld_stab.  I think the only way to determine the
 161      number of relocs is to assume that all the bytes from ld_rel to
 162      ld_hash contain reloc entries.  */
 163   unsigned long ld_rel;
 164
 165   /* The address of a hash table of symbols.  The hash table has
 166      roughly the same number of entries as there are dynamic symbols;
 167      I think the only way to get the exact size is to assume that
 168      every byte from ld_hash to ld_stab is devoted to the hash table.
 169
 170      Each entry in the hash table is eight bytes.  The first four
 171      bytes are a symbol index into the dynamic symbols.  The second
 172      four bytes are the index of the next hash table entry in the
 173      bucket.  The ld_buckets field gives the number of buckets, say B.
 174      The first B entries in the hash table each start a bucket which
 175      is chained through the second four bytes of each entry.  A value
 176      of zero ends the chain.
 177
 178      The hash function is simply
 179          h = 0;
 180          while (*string != '\0')
 181            h = (h << 1) + *string++;
 182          h &= 0x7fffffff;
 183
 184      To look up a symbol, compute the hash value of the name.  Take
 185      the modulos of hash value and the number of buckets.  Start at
 186      that entry in the hash table.  See if the symbol (from the first
 187      four bytes of the hash table entry) has the name you are looking
 188      for.  If not, use the chain field (the second four bytes of the
 189      hash table entry) to move on to the next entry in this bucket.
 190      If the chain field is zero you have reached the end of the
 191      bucket, and the symbol is not in the hash table.  */
 192   unsigned long ld_hash;
 193
 194   /* The address of the symbol table.  This is a list of
 195      external_nlist structures.  The string indices are relative to
 196      the ld_symbols field.  I think the only way to determine the
 197      number of symbols is to assume that all the bytes between ld_stab
 198      and ld_symbols are external_nlist structures.  */
 199   unsigned long ld_stab;
 200
 201   /* I don't know what this is for.  It seems to always be zero.  */
 202   unsigned long ld_stab_hash;
 203
 204   /* The number of buckets in the hash table.  */
 205   unsigned long ld_buckets;
 206
 207   /* The address of the symbol string table.  The first string in this
 208      string table need not be the empty string.  */
 209   unsigned long ld_symbols;
 210
 211   /* The size in bytes of the symbol string table.  */
 212   unsigned long ld_symb_size;
 213
 214   /* The size in bytes of the text segment.  */
 215   unsigned long ld_text;
 216
 217   /* The size in bytes of the procedure linkage table.  */
 218   unsigned long ld_plt_sz;
 219 };
 220
 221 /* The external form of the structure.  */
 222
 223 struct external_sun4_dynamic_link
 224 {
 225   bfd_byte ld_loaded[4];
 226   bfd_byte ld_need[4];
 227   bfd_byte ld_rules[4];
 228   bfd_byte ld_got[4];
 229   bfd_byte ld_plt[4];
 230   bfd_byte ld_rel[4];
 231   bfd_byte ld_hash[4];
 232   bfd_byte ld_stab[4];
 233   bfd_byte ld_stab_hash[4];
 234   bfd_byte ld_buckets[4];
 235   bfd_byte ld_symbols[4];
 236   bfd_byte ld_symb_size[4];
 237   bfd_byte ld_text[4];
 238   bfd_byte ld_plt_sz[4];
 239 };