ldfcn - Common object file access routines
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 cal-
ling program from knowledge of the overall structure of the object file.
The interface between the calling program and the object file access rou-
tines 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 struc-
ture to the calling program. The fields of the LDFILE structure can be
accessed individually through macros defined in ldfcn.h. The fields con-
tain the following information:
TYPE(ldptr) The file magic number, used to distinguish between archive
members and simple object files.
IOPTR(ldptr) Not used because files are memory mapped.
OFFSET(ldptr) 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.
HEADER(ldptr) The file header structure of the object file.
The symbolic header structure for the symbol table associ-
ated with the object file.
PFD(ldptr) The file table associated with the symbol table.
SYMTAB(ldptr) 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.)
LDSWAP(ldptr) 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
The object file access functions can be divided into four categories:
1. Functions that open or close an object file:
- ldopen and ldaopen open an object file.
- ldclose and ldaclose close an object file.
2. Functions that return header or symbol table information:
- ldahread reads the archive 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
- ldgetpd retrieves a procedure descriptor.
3. 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 sec-
tion 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
- ldtbseek seeks to the symbol table of an object file.
4. 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.
- ranlookup 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 struc-
Additional access to an object file is provided through a set of macros
defined in ldfcn.h. These macros parallel the standard input/output 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:
FGETS(s, n, ldptr)
FREADM((char *) ptr, sizeof (*ptr), nitems, ldptr)
FSEEK(ldptr, offset, ptrname)
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 archive file
cannot be the same as the end of one of its object file members.
Functions: fopen(3), fseek(3), ldahread(3), ldclose(3), ldfhread(3), ldget-
name(3), ldlseek(3), ldohseek(3), ldopen(3), ldrseek(3), ldshread(3),