OBJECT(2) OBJECT(2)
NAME
objtype, readobj, objtraverse, isar, nextar, readar - object
file interpretation functions
SYNOPSIS
#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)
DESCRIPTION
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 exe-
cutable files and executing images.
Object files contain no formal symbol table; instead, refer-
ences to symbols must be extracted from the encoded object
representation and resolved. The resulting symbol informa-
tion is loaded into a dummy symbol table where it is avail-
able 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 defining 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 interme-
diate object file. If it is, a code indicating the archi-
tecture type of the file is returned and the second argu-
ment, 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 posi-
tion after decoding the header.
Readobj constructs a symbol table for the object file
Page 1 Plan 9 (printed 12/21/24)
OBJECT(2) OBJECT(2)
associated with bp. The second argument contains the type
code produced by function objtype. The file must be posi-
tioned at the start of the object file. Each invocation of
readobj destroys the symbol definitions 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 asso-
ciated 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 SARNAME 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 differ-
ence 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.
SOURCE
/sys/src/libmach
SEE ALSO
mach(2), symbol(2), bio(2), a.out(6)
DIAGNOSTICS
These routines set errstr.
Page 2 Plan 9 (printed 12/21/24)