Assembler Questions | Compiler Design

1st pass: scan label definitions and assign addresses
2nd pass: actual translation (object code)

Pass 1 : define symbols (assign addresses)

• Assign addresses to all statements in the program
• Save the values assigned to all labels for use in Pass 2
• Process some assembler directives
• Table creation , Adding literals to literal table
• Allocate space for literals
• Compute total length of a program

Pass 2 : assemble instructions and generate object program

• Assemble instructions
• Generate data values defined by BYTE, WORD, etc.
• Process the assembler directives not done in Pass 1
• Write the object program and the assembly listing

Finally, assembler must write the generated object code to some output device
- Called object program
- Will be later loaded into memory for execution

A single pass assembler scans the program only once and creates the equivalent binary program

Pseudo Instructions are special commands to the assembler about the positioning of the program, the address the program should presumed to be assembled at, the name of the module, data declarations, the title and printing options for the program, defining and calling macros, macro looping and test, and end of source code. Unless a machine instruction is issued, these do not generate executable code.

Refer : https://en.wikibooks.org/wiki/360_Assembly/Pseudo_Instructions

option A,B,C are included.

option A,B,C are included.

• In two pass assembler the symbol table is used to store memory locations
• The symbol table contains information to locate and relocate symbolic definitions and references. The assembler creates the symbol table section for the object file. It makes an entry in the symbol table for each symbol that is defined or referenced in the input file and is needed during linking.
• The symbol table is then used by the link editor during relocation. The symbol table's section header contains the symbol table index for the first non-local symbol.
• Instead of using an absolute memory address it uses a symbolic address.

• A general-purpose macro processor or general purpose preprocessor is a macro processor that is not tied to or integrated with a particular language or piece of software.
• A macro processor is a program that copies a stream of text from one place to another, making a systematic set of replacements as it does so.
• Macro processors are often embedded in other programs, such as assemblers and compilers. Sometimes they are standalone programs that can be used to process any kind of text.
• Macro processors have been used for language expansion (defining new language constructs that can be expressed in terms of existing language components), for systematic text replacements that require decision making, and for text reformatting (e.g. conditional extraction of material from an HTML file).

option A,B,C are included.

An assembler directive is a message to the assembler that tells the assembler something it needs to know in order to carry out the assembly process; for example, an assemble directive test the assembler where a program is to be located in memory.
Basic Assembly directives
EQU →Equate
ORG →Origin
START → Start (Define the start of the first control section in a program)
END → End (End of assembly language program and "starting address" for execution)

• Assembly languages are hardware dependent; there is a different one for each CPU series.
• Assembly language (or Assembler) is a compiled, low-level computer language. It is processor-dependent, since it basically translates the Assembler's mnemonics directly into the commands a particular CPU understands, on a one-to-one basis.
• These Assembler mnemonics are the instruction set for that processor

C is the useless variable as there is no production rule which replaces C with a terminal. Thus, it does not derive any non terminal.