Implementing Examples By Prof Nousheen Taj Asst Professor

Implementing Examples By Prof. Nousheen Taj Asst. Professor, Dept. of CSE

MS DOS Linker Most MS-DOS compilers and assemblers produce object modules. n. OBJ files contain a binary image of the translated instructions and data program. n MS-DOS LINK is a linkage editor. n Produces. EXE files. n

MS DOS Linker n object file (. OBJ) n n generated by assembler (or compiler) format THEADR name of this object module PUBDEF external symbols defined in this module EXTDEF external symbols used here TYPDEF data types for pubdef and extdef SEGDEF describes segments in this module GRPDEF segment grouping LNAMES name list indexed by segdef and grpdef LEDATA binary image of code LIDATA repeated data FIXUPP modification record MODEND end

MS DOS Linker (cont’d) n LINK n pass 1: • allocates segments defined in SEGDEF • resolve external symbols n pass 2: • prepare memory image • if needed, disk space is also used • expand LIDATA • relocations within segment • write. EXE file

Sun. OS linkers for SPARC n n Linkers: link-editor and run-time linker Object files: n A relocatable object module, suitable for further linkediting. n A static executable, with all symbolic references bound and ready to run. n A dynamic executable, in which some symbolic references may need to be bound at run time. n A shared object, which provides services that can be bound at run time to one ore more dynamic executables.

Sun. OS linkers for n n n Object modules contain one or more sections. Sections has a set of attributes such as executable and writeable. Sections that have the same attributes are concatenated to form new sections with in the output file. The linker normally generates a new symbol table and new set of relocation instructions, with in output file, to represent the symbols that must be bound at run time. Uses 11 different relocation codes that reflects instruction formats and addressing modes too. Symbolic references from the input files that do not have matching definitions are processed by referring to archives and shared objects.

Cray MPP Linker for Cray T 3 E n n n T 3 E system contains a large number of processing elements. Each PE can access the memory of all other Pes. An application program is allocated to a partition that consists of several Pes. The work of the program is divided between the PEs in the partition. One common way to accomplish this is to distribute the elements of an array among the Pes.

Problems… n n There may be live objects that are instances of a class we want to reload. The application may be executing a method that belongs to a class we want to reload. v By organizing software components in separate class loaders, we can solve these problems.