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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: LDFILE *ldptr; 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. SYMHEADER(ldptr) The symbolic header structure for the symbol table associated 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 are swapped.) 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 ldptr. - 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 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. 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 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. 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), ldlread(3), ldlseek(3), ldohseek(3), ldopen(3), ldrseek(3), ldshread(3), ldtbread(3), ldtbseek(3).