ldfcn man page on DigitalUNIX

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ldfcn(4)							      ldfcn(4)

       ldfcn - Common object file access routines

       #include	 <stdio.h>  #include  <filehdr.h>  #include  <syms.h> #include

       The common object file access routines are a  collection	 of  functions
       for  reading  an object file that is in common object file form (COFF).
       Although the calling program must know the detailed  structure  of  the
       parts  of  the  object file that it processes, the routines effectively
       insulate the calling program from knowledge of the overall structure of
       the object file.

       The  interface  between	the calling program and the object file access
       routines is based  on  the  defined  type  LDFILE  (defined  as	struct
       ldfile), which is declared in the header file ldfcn.h.  Primarily, this
       structure provides uniform access to simple  object  files  and	object
       files that are members of an archive file.

       The  function  ldopen  allocates	 and initializes the LDFILE structure,
       reads in the symbol table header, if present, and returns a pointer  to
       the  structure to the calling program.  The fields of the LDFILE struc‐
       ture can be accessed individually through macros	 defined  in  ldfcn.h.
       The  fields  contain  the following information: The file magic number,
       used to distinguish between archive members and	simple	object	files.
       Not  used  because  files  are  memory mapped.  The file address of the
       beginning of the object file or archive entry; if the object file is  a
       member  of  an  archive	file,  the offset is nonzero.  The file header
       structure of the object file.  The symbolic header  structure  for  the
       symbol  table  associated with the object file.	The file table associ‐
       ated with the symbol table.  A pointer to a copy of the symbol table in
       memory.	  It   is   accessed   through	 the   pCHDR   structure  (see
       /usr/include/cmplrs/stsupport.h).  If no symbol table is present,  this
       field  is  NULL.	 (Note: This macro causes the whole symbol table to be
       read.)  If the header and symbol table structures  are  swapped	within
       the object file and all access requires using libsex, this field is set
       to true.	 (Note: If you use libmld routines, all structures except  the
       optional header and auxiliaries are swapped.)

       The  object  file access functions can be divided into four categories:
       Functions that open or close an object file: ldopen and ldaopen open an
       object  file.   ldclose	and  ldaclose close an object file.  Functions
       that return header or symbol table information: ldahread reads the  ar‐
       chive  header  of a member of an archive file.  ldfhread reads the file
       header of an object file.  ldshread and ldnshread read a section header
       of  an  object  file.  ldtbread reads a symbol table entry of an object
       file.  ldgetname retrieves a symbol name from a symbol table  entry  or
       from the string table.  ldgetaux retrieves a pointer into the aux table
       for the specified ldptr.	 ldgetpd  retrieves  a	procedure  descriptor.
       Functions  that	seek to specified portions of an object file: ldohseek
       seeks to the optional file  header  of  an  object  file.  ldsseek  and
       ldnsseek	 seek  to  a  section of an object file.  ldrseek and ldnrseek
       seek to the relocation information for a section	 of  an	 object	 file.
       ldlseek	and ldnlseek seek to the line number information for an object
       file.  ldlseek and ldnlseek ignore section number and  name  arguments,
       respectively.   ldtbseek	 seeks	to the symbol table of an object file.
       Miscellaneous functions ranhashinit (see	 ranhash(3))  initializes  the
       tables  and  constants so that the archive hash and lookup routines can
       work.  Given a string, ranhash returns the hash	index  for  it.	  ran‐
       lookup  returns	an  archive  hash  bucket that is empty or matches the
       string argument.	 disassembler prints assembly instructions.

       These functions are described in detail in their own reference pages.

       The ldopen and ldaopen functions	 both  return  pointers	 to  a	LDFILE

       Additional access to an object file is provided through a set of macros
       defined in ldfcn.h.  These macros  parallel  the	 standard  inputoutput
       file reading and manipulating functions.	 They translate a reference of
       the LDFILE structure into a reference to its file descriptor field.

       The following macros are provided: GETC(ldptr) FGETC(ldptr) GETW(ldptr)
       UNGETC(c, ldptr) FGETS(s, n, ldptr) FREADM((char *) ptr, sizeof (*ptr),
       nitems, ldptr) FSEEK(ldptr, offset, ptrname) FTELL(ldptr) REWIND(ldptr)
       FEOF(ldptr)  FERROR(ldptr)  FILENO(ldptr)  SETBUF(ldptr,	 buf)  STROFF‐

       The STROFFSET macro calculates the address of the local symbol's string
       table in an object file.	 See the reference pages for the corresponding
       standard input/output library functions for details on the use of these

       The  program must be loaded with the object file access routine library

       The FSEEK macro defined in the header file ldfcn.h  translates  into  a
       call  to the standard input/output function fseek.  FSEEK should not be
       used to seek from the end of an archive file because the end of an  ar‐
       chive file cannot be the same as the end of one of its object file mem‐

       Commands: ar(1)

       Functions: fopen(3), fseek(3),  ldahread(3),  ldclose(3),  ldfhread(3),
       ldgetname(3),	ldlseek(3),    ldohseek(3),   ldopen(3),   ldrseek(3),
       ldshread(3), ldtbread(3), ldtbseek(3).  delim off


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