LDFCN(4) — Silicon Graphics not on PDP-11

NAME

ldfcn − common object file access routines

SYNOPSIS

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

DESCRIPTION

The common object file access routines are a collection of functions for reading an object file that is in VAX or 3B20S (common) object file form. 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.

OPTR(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

open a common object file

ldclose(3X) and ldaclose

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

read a section header of a common object file

ldtbread(3X)

read a symbol table entry of a common object file

(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

seek to a section of a common object file

ldrseek(3X) and ldnrseek

seek to the relocation information for a section of a common object file

ldlseek(3X) and ldnlseek

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 function ldtbindex(3X) which returns the index of a particular common object file symbol table entry

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

All the functions except ldopen, ldaopen and ldtbindex return either SUCCESS or FAILURE, both constants defined in ldfcn.h. Ldopen and ldaopen both return pointers to a LDFILE structure.

MACROS

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:

LDFILE∗ldptr;

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)

See the manual entries for the corresponding standard input/output library functions for details on the use of these macros.

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

CAVEAT

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!

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