Mumbai University > Computer Engineering > Sem6 > System Programming and Compiler Construction

Marks: 5M

Year: May 2012

Assembler

• Assembler is the language translator that accepts inputs as assembly language (ALP) and obtains its machine equivalent code (Object code) along with the information required by the loader.
• ALP is low-level language .The execution of statements can be done line by line.
• Diagram

ALP Machine Language Information for Loader

Reasons for assembler to be Multipass

• Multipass assembler means more than one pass is used by assembler.
• Multipass assembler is used to eliminate forward references in symbol definition.
• Forward References Problem - The assembler specifies the symbols should be declared anywhere in the in the program.
• There may be a chances of using a symbol before its declaration which gives rise to a forward reference problem.
• Due to this problem assembler won’t be able to assemble the instruction and such a problem is called forward references problem
• The solution for forward references problem is having an assembler of two pass.
• It creates a number of passes that is necessary to process the definition of symbols.
• In pass one we find out all the Symbols and Literals.
• And in pass two we will perform assembling of code and the data (generating instruction and generating data).