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OBJECT(2)										OBJECT(2)

       objtype, readobj, objtraverse, isar, nextar, readar - object file interpretation functions

       #include <u.h>
       #include <libc.h>
       #include <bio.h>
       #include <mach.h>

       int  objtype(Biobuf *bp, char **name)

       int  readobj(Biobuf *bp, int objtype)

       void  objtraverse(void(*)(Sym*, void*), void*)

       int isar(Biobuf *bp)

       int nextar(Biobuf *bp, int offset, char *buf)

       int readar(Biobuf *bp, int objtype, int end)

       These  functions  provide  machine-independent access to object files in a directory or an
       archive.  Mach(2) and symbol(2) describe additional  library  functions	for  interpreting
       executable files and executing images.

       Object  files  contain  no  formal  symbol  table;  instead, references to symbols must be
       extracted from the encoded object  representation  and  resolved.   The	resulting  symbol
       information is loaded into a dummy symbol table where it is available for processing by an
       application.  The organization of the dummy symbol table is identical to that produced  by
       the loader and described in symbol(2) and a.out(6): a vector of Sym data structures defin-
       ing the name, type and relative offset of each symbol.

       Objtype reads the header at the current position of  the  file  associated  with  bp  (see
       Bio(2))	to  see  if  it  is an intermediate object file.  If it is, a code indicating the
       architecture type of the file is returned and the second argument, if it is  non-zero,  is
       set pointing to a string describing the type of the file.  If the header does not indicate
       an object file, -1 is returned.	The header may be at the start of an object  file  or  at
       the  beginning  of  an archive member.  The file is rewound to its starting position after
       decoding the header.

       Readobj constructs a symbol table for the object file  associated  with	bp.   The  second
       argument contains the type code produced by function objtype.  The file must be positioned
       at the start of the object file.  Each invocation of readobj destroys the  symbol  defini-
       tions for any previous file.

       Objtraverse  scans  the	symbol	table previously built by readobj or readar.  Objtraverse
       requires two arguments: the address of a call-back function and a  generic  pointer.   The
       call-back function is invoked once for each symbol in the symbol table with the address of
       a Sym data structure as the first argument and the generic pointer as the second.

       Isar reads the header at the current point in the file associated with bp and returns 1 if
       it  is  an  archive  or	zero otherwise.  The file is positioned at the end of the archive
       header and at the beginning of the first member of the archive.

       Nextar extracts information describing the archive member stored at  offset  in	the  file
       associated with bp.  If the header describing the member can be extracted and decoded, the
       size of the member is returned.	Adding this value to offset  yields  the  offset  of  the
       beginning  of  the  next member in the archive.	On return the input file is positioned at
       the end of the member header and the name of the member is stored in buf, a buffer of SAR-
       NAME  characters.   If  there  are no more members, nextar returns zero; a negative return
       indicates a missing or malformed header.

       Readar constructs the symbol table of the object file stored at the  current  position  in
       the  archive associated with bp.  This function operates exactly as readobj; the only dif-
       ference is the extra argument, end, specifying the offset to the  beginning  of	the  next
       member in the archive.  Readar leaves the file positioned at that point.


       mach(2), symbol(2), bio(2), a.out(6)

       These routines set errstr.

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