LDFCN(3)

NAME
ldfcn - common object file access routines

SYNOPSIS
#include <stdio.h>
#include <filehdr.h>
#include <ldfcn.h>

AVAILABILITY

Available only on Sun 386i systems running a SunOS 4.0.x release or earlier. Not a SunOS 4.1 release feature.

DESCRIPTION

These routines are for reading COFF object files and archives containing COFF object files. 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, declared in the header file ldfcn.h. The primary purpose of this structure is to provide uniform access to both simple object files and to object files that are members of an archive file.

The function ldopen(3X) allocates and initializes the LDFILE structure and returns a pointer to the structure to the calling program. The fields of the LDFILE structure may be accessed individually through macros defined in ldfcn.h and contain the following information:

LDFILE		*ldptr;

TYPE(ldptr)
    The file magic number used to distinguish between archive members and simple object files.

IOPTR(ldptr)
    The file pointer returned by fopen and used by the standard input/output functions.

OFFSET(ldptr)
    The file address of the beginning of the object file; the offset is non-zero if the object file is a member of an archive file.

HEADER(ldptr)
    The file header structure of the object file.

The object file access functions themselves may be divided into four categories:

    (1) Functions that open or close an object file

        ldopen(3X) and ldaopen() (see ldopen(3X))
            open a common object file
        ldclose(3X) and ldaclose() (see ldclose(3X))
            close a common object file

    (2) Functions that read header or symbol table information

        ldahread(3X)
            read the archive header of a member of an archive file
        ldfhread(3X)
            read the file header of a common object file
        ldshread(3X) and ldnshread() (see ldshread(3X))
            read a section header of a common object file
        ldtbread(3X)
            read a symbol table entry of a common object file
        ldgetname(3X)
            retrieve a symbol name from a symbol table entry or from the string table

    (3) Functions that position an object file at (seek to) the start of the section, relocation, or line number information for a particular section.

        ldohseek(3X)
            seek to the optional file header of a common object file
        ldsseek(3X) and ldnsseek() (see ldsseek(3X))
            seek to a section of a common object file
        ldrseek(3X) and ldnrseek() (see ldrseek(3X))
            seek to the relocation information for a section of a common object file
        ldlseek(3X) and ldnlseek() (see ldlseek(3X))
            seek to the line number information for a section of a common object file
        ldtbseek(3X)
            seek to the symbol table of a common object file

    (4) The unction ldtbindex(3X), which returns the index of a particular common object file symbol table entry.

These functions are described in detail on their respective manual pages.

All the functions except ldopen(3X), ldgetname(3X), ldtbindex(3X) return either SUCCESS or FAILURE, both constants defined in ldfcn.h. ldopen(3X) and ldaopen() (see ldopen(3X)) both return pointers to an LDFILE structure.

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, translating 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)
    FREAD((char *) ptr, sizeof (*ptr), nitems, ldptr)
    FSEEK(ldptr, offset, ptrname)
    FTELL(ldptr)
    REWIND(ldptr)
    FEOF(ldptr)
    FERROR(ldptr)
    FILENO(ldptr)
    SETBUF(ldptr, buf)
    STROFFSET(ldptr)

The STROFFSET macro calculates the address of the string table. See the manual entries for the corresponding standard input/output library functions for details on the use of the rest of the macros.

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

SEE ALSO
fseek(3S), ldahread(3X), ldclose(3X), ldgetname(3X), ldfhread(3X), ldlread(3X), ldlseek(3X), ldohseek(3X), ldopen(3X), ldrseek(3X), ldlseek(3X), ldshread(3X), ldtbindex(3X), ldtbread(3X), ldtbseek(3X), stdio(3V), intro(5)

WARNING

The macro FSEEK defined in the header file ldfcn.h translates into a call to the standard input/output function fseek(3S). FSEEK should not be used to seek from the end of an archive file since the end of an archive file may not be the same as the end of one of its object file members.