ldfcn - Common object file access routines
#include <stdio.h> #include <filehdr.h> #include <syms.h>
#include <ldfcn.h>
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 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), 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 structure to the calling program.
The fields of the LDFILE structure can be accessed
individually through macros defined in ldfcn.h. The
fields contain the following information: The file magic
number, used to distinguish between archive members and
simple object files. Not used because files are memory
mapped. 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. The file header
structure of the object file. The symbolic header structure
for the symbol table associated with the object file.
The file table associated with the symbol table. 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.) 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 are swapped.)
The object file access functions can be divided into four
categories: Functions that open or close an object file:
ldopen and ldaopen open an object file. ldclose and ldaclose
close an object file. 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 ldptr. ldgetpd retrieves a procedure
descriptor. 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 section 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 arguments, respectively. ldtbseek seeks
to the symbol table of an object file. 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 structure.
Additional access to an object file is provided through a
set of macros defined in ldfcn.h. These macros parallel
the standard inputoutput 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: GETC(ldptr)
FGETC(ldptr) GETW(ldptr) UNGETC(c, ldptr) FGETS(s, n,
ldptr) FREADM((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 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 macros.
The program must be loaded with the object file access
routine library libmld.a.
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.
Commands: ar(1)
Functions: fopen(3), fseek(3), ldahread(3), ldclose(3),
ldfhread(3), ldgetname(3), ldlseek(3), ldohseek(3),
ldopen(3), ldrseek(3), ldshread(3), ldtbread(3), ldtbseek(3). delim off
ldfcn(4)
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