Subversion Repositories openrisc_2011-10-31

/* SPARC-specific values for a.out files

   Copyright 2001 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 2 of the License, or

   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program; if not, write to the Free Software

   Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.  */

/* Some systems, e.g., AIX, may have defined this in header files already

   included.  */

#undef  TARGET_PAGE_SIZE

#define TARGET_PAGE_SIZE        0x2000          /* 8K.  aka NBPG in <sys/param.h> */

/* Note that some SPARCs have 4K pages, some 8K, some others.  */

#define SEG_SIZE_SPARC  TARGET_PAGE_SIZE

#define SEG_SIZE_SUN3   0x20000         /* Resolution of r/w protection hw */

#define TEXT_START_ADDR TARGET_PAGE_SIZE        /* Location 0 is not accessible */

#define N_HEADER_IN_TEXT(x) 1

/* Non-default definitions of the accessor macros... */

/* Segment size varies on Sun-3 versus Sun-4.  */

#define N_SEGSIZE(x)    (N_MACHTYPE(x) == M_SPARC?      SEG_SIZE_SPARC: \

                         N_MACHTYPE(x) == M_68020?      SEG_SIZE_SUN3:  \

                        /* Guess? */                    TARGET_PAGE_SIZE)

/* Virtual Address of text segment from the a.out file.  For OMAGIC,

   (almost always "unlinked .o's" these days), should be zero.

   Sun added a kludge so that shared libraries linked ZMAGIC get

   an address of zero if a_entry (!!!) is lower than the otherwise

   expected text address.  These kludges have gotta go!

   For linked files, should reflect reality if we know it.  */

/* This differs from the version in aout64.h (which we override by defining

   it here) only for NMAGIC (we return TEXT_START_ADDR+EXEC_BYTES_SIZE;

   they return 0).  */

#define N_TXTADDR(x) \

    (N_MAGIC(x)==OMAGIC? 0 \

     : (N_MAGIC(x) == ZMAGIC && (x).a_entry < TEXT_START_ADDR)? 0 \

     : TEXT_START_ADDR+EXEC_BYTES_SIZE)

/* When a file is linked against a shared library on SunOS 4, the

   dynamic bit in the exec header is set, and the first symbol in the

   symbol table is __DYNAMIC.  Its value is the address of the

   following structure.  */

struct external_sun4_dynamic

{

  /* The version number of the structure.  SunOS 4.1.x creates files

     with version number 3, which is what this structure is based on.

     According to gdb, version 2 is similar.  I believe that version 2

     used a different type of procedure linkage table, and there may

     have been other differences.  */

  bfd_byte ld_version[4];

  /* The virtual address of a 28 byte structure used in debugging.

     The contents are filled in at run time by ld.so.  */

  bfd_byte ldd[4];

  /* The virtual address of another structure with information about

     how to relocate the executable at run time.  */

  bfd_byte ld[4];

};

/* The size of the debugging structure pointed to by the debugger

   field of __DYNAMIC.  */

#define EXTERNAL_SUN4_DYNAMIC_DEBUGGER_SIZE (24)

/* The structure pointed to by the linker field of __DYNAMIC.  As far

   as I can tell, most of the addresses in this structure are offsets

   within the file, but some are actually virtual addresses.  */

struct internal_sun4_dynamic_link

{

  /* Linked list of loaded objects.  This is filled in at runtime by

     ld.so and probably by dlopen.  */

  unsigned long ld_loaded;

  /* The address of the list of names of shared objects which must be

     included at runtime.  Each entry in the list is 16 bytes: the 4

     byte address of the string naming the object (e.g., for -lc this

     is "c"); 4 bytes of flags--the high bit is whether to search for

     the object using the library path; the 2 byte major version

     number; the 2 byte minor version number; the 4 byte address of

     the next entry in the list (zero if this is the last entry).  The

     version numbers seem to only be non-zero when doing library

     searching.  */

  unsigned long ld_need;

  /* The address of the path to search for the shared objects which

     must be included.  This points to a string in PATH format which

     is generated from the -L arguments to the linker.  According to

     the man page, ld.so implicitly adds ${LD_LIBRARY_PATH} to the

     beginning of this string and /lib:/usr/lib:/usr/local/lib to the

     end.  The string is terminated by a null byte.  This field is

     zero if there is no additional path.  */

  unsigned long ld_rules;

  /* The address of the global offset table.  This appears to be a

     virtual address, not a file offset.  The first entry in the

     global offset table seems to be the virtual address of the

     sun4_dynamic structure (the same value as the __DYNAMIC symbol).

     The global offset table is used for PIC code to hold the

     addresses of variables.  A dynamically linked file which does not

     itself contain PIC code has a four byte global offset table.  */

  unsigned long ld_got;

  /* The address of the procedure linkage table.  This appears to be a

     virtual address, not a file offset.

     On a SPARC, the table is composed of 12 byte entries, each of

     which consists of three instructions.  The first entry is

         sethi %hi(0),%g1

         jmp %g1

         nop

     These instructions are changed by ld.so into a jump directly into

     ld.so itself.  Each subsequent entry is

         save %sp, -96, %sp

         call <address of first entry in procedure linkage table>

         <reloc_number | 0x01000000>

     The reloc_number is the number of the reloc to use to resolve

     this entry.  The reloc will be a JMP_SLOT reloc against some

     symbol that is not defined in this object file but should be

     defined in a shared object (if it is not, ld.so will report a

     runtime error and exit).  The constant 0x010000000 turns the

     reloc number into a sethi of %g0, which does nothing since %g0 is

     hardwired to zero.

     When one of these entries is executed, it winds up calling into

     ld.so.  ld.so looks at the reloc number, available via the return

     address, to determine which entry this is.  It then looks at the

     reloc and patches up the entry in the table into a sethi and jmp

     to the real address followed by a nop.  This means that the reloc

     lookup only has to happen once, and it also means that the

     relocation only needs to be done if the function is actually

     called.  The relocation is expensive because ld.so must look up

     the symbol by name.

     The size of the procedure linkage table is given by the ld_plt_sz

     field.  */

  unsigned long ld_plt;

  /* The address of the relocs.  These are in the same format as

     ordinary relocs.  Symbol index numbers refer to the symbols

     pointed to by ld_stab.  I think the only way to determine the

     number of relocs is to assume that all the bytes from ld_rel to

     ld_hash contain reloc entries.  */

  unsigned long ld_rel;

  /* The address of a hash table of symbols.  The hash table has

     roughly the same number of entries as there are dynamic symbols;

     I think the only way to get the exact size is to assume that

     every byte from ld_hash to ld_stab is devoted to the hash table.

     Each entry in the hash table is eight bytes.  The first four

     bytes are a symbol index into the dynamic symbols.  The second

     four bytes are the index of the next hash table entry in the

     bucket.  The ld_buckets field gives the number of buckets, say B.

     The first B entries in the hash table each start a bucket which

     is chained through the second four bytes of each entry.  A value

     of zero ends the chain.

     The hash function is simply

         h = 0;

         while (*string != '\0')

           h = (h << 1) + *string++;

         h &= 0x7fffffff;

     To look up a symbol, compute the hash value of the name.  Take

     the modulos of hash value and the number of buckets.  Start at

     that entry in the hash table.  See if the symbol (from the first

     four bytes of the hash table entry) has the name you are looking

     for.  If not, use the chain field (the second four bytes of the

     hash table entry) to move on to the next entry in this bucket.

     If the chain field is zero you have reached the end of the

     bucket, and the symbol is not in the hash table.  */

  unsigned long ld_hash;

  /* The address of the symbol table.  This is a list of

     external_nlist structures.  The string indices are relative to

     the ld_symbols field.  I think the only way to determine the

     number of symbols is to assume that all the bytes between ld_stab

     and ld_symbols are external_nlist structures.  */

  unsigned long ld_stab;

  /* I don't know what this is for.  It seems to always be zero.  */

  unsigned long ld_stab_hash;

  /* The number of buckets in the hash table.  */

  unsigned long ld_buckets;

  /* The address of the symbol string table.  The first string in this

     string table need not be the empty string.  */

  unsigned long ld_symbols;

  /* The size in bytes of the symbol string table.  */

  unsigned long ld_symb_size;

  /* The size in bytes of the text segment.  */

  unsigned long ld_text;

  /* The size in bytes of the procedure linkage table.  */

  unsigned long ld_plt_sz;

};

/* The external form of the structure.  */

struct external_sun4_dynamic_link

{

  bfd_byte ld_loaded[4];

  bfd_byte ld_need[4];

  bfd_byte ld_rules[4];

  bfd_byte ld_got[4];

  bfd_byte ld_plt[4];

  bfd_byte ld_rel[4];

  bfd_byte ld_hash[4];

  bfd_byte ld_stab[4];

  bfd_byte ld_stab_hash[4];

  bfd_byte ld_buckets[4];

  bfd_byte ld_symbols[4];

  bfd_byte ld_symb_size[4];

  bfd_byte ld_text[4];

  bfd_byte ld_plt_sz[4];

};