PN —name of the program starting address of the program. What are the basic functions of loaders Loading — brings the object program into memory for execution Relocation — modifies the object program so that it can be loaded at an address different from the location originally specified Linking — combines two or more separate object programs and also supplies the information needed to reference them. Define absolute loader The loader, which is used only for loading, is known as absolute loader. Bootstrap loader What is meant by bootstrap loader?
|Published (Last):||28 June 2015|
|PDF File Size:||12.33 Mb|
|ePub File Size:||14.25 Mb|
|Price:||Free* [*Free Regsitration Required]|
The test device TD instruction tests whether the addressed device is ready to send or receive a byte of data. The condition code is set to indicate the result of this test.
Define the basic functions of assembler. What is meant by assembler directives. Give example. These are the statements that are not translated into machine instructions,but they provide instructions to assembler itself. What is forward references?
It is a reference to a label that is defined later in a program. If we attempt to translate the program line by line,we will unable to process the statement in line 10 because we do not know the address that will be assigned to RETADR.
The address is assigned later in line 80 in the program. What are the three different records used in object program? The header record,text record and the end record are the three different records used in object program. The header record contains the program name,starting address and length of the program. Text record contains the translated instructions and data of the program. End record marks the end of the object program and specifies the address in the program where execution is to begin.
The symbol table includes the name and value for each symbol in the source program,together with flags to indicate error conditions. Some times it may contains details about the data area.
The operation code table contain the mnemonic operation code and its machine language equivalent. Some assemblers it may also contains information about instruction format and length.
OPTAB is usually organized as a hash table,with mnemonic operation code as the key. What are the symbol defining statements generally used in assemblers? When this statement is encountered the assembler resets its location counter to the specified value. The general format is ORG value In the above two statements value is a constant or an expression involving constants and previously defined symbols.
Define relocatable program. An object program that contains the information necessary to perform required modification in the object code depends on the starting location of the program during load time is known as relocatable program.
Differentiate absolute expression and relative expression. If the result of the expression is an absolute value constant then it is known as absolute expression. Write the steps required to translate the source program to object program. This variable is used to assign addresses to the symbols.
Aftre each source statement is processed the length of the assembled instruction or data area to be generated is added to LOCCTR and hence whenever we reach a label in the source program the current value of LOCCTR gives the address associated with the label. Define load and go assembler.
One pass assembler that generate their object code in memory for immediate execution is known as load and go assembler. Here no object programmer is written out and hence no need for loader.
What are the two different types of jump statements used in MASM assembler. Near jump A near jump is a jump to a target in the same segment and it is assembled by using a current code segment CS. Far jump A far jump is a jump to a target in a different code segment and it is assembled by using different segment registers. What are the use of base register table in AIX assembler? A base register table is used to remember which of the general purpose registers are currently available as base registers and also the base addresses they contain.
USING statement causes entry to the table and. DROP statement removes the corresponding table entry. RESW —It reserves the indicated number of words for data area. If the memory is byte addressable then the address assigned for the next symbol is RESB —It reserves the indicated number of bytes for data area. Hence the address assigned for the next symbol is Define modification record and give its format This record contains the information about the modification in the object code during program relocation.
Object code generation b. Literals added to literal table c. Listing printed d. Address location of local symbols Answer: a. Object code generation - PASS 2 b. Literals added to literal table — PASS 1 c. Listing printed — PASS2 d. Address location of local symbols — PASS 1 What is meant by machine independent assembler features? The assembler features that does not depends upon the machine architecture are known as machine independent assembler features.
Eg: program blocks,Literals. How the register to register instructions are translated in assembler? In the case of register to register instructions the operand field contains the register name. During the translation first the object code is converted into its corresponding machine language equivalent with the help of OPTAB. What is meant by external references? Assembler program can be divided into many sections known as control sections and each control section can be loaded and relocated independently of the others.
If the instruction in one control section need to refer instruction or data in another control section. Such references between control are called external references. Define control section.
A control section is a part of the program that maintain its identity after assembly;each control section can be loaded and relocated independently of the others. Control sections are most often used for subroutines. The major benefit of using control sections is to increase flexibility. EXTDEF names external symbols that are defined in a particular control section and may be used by other sections. EXTREF names external symbols that are referred in a particular control section and defined in another control section.
Give the general format of define record. This record gives information about external symbols that are defined in a particular control section. The format is Col 1 D Col name of external symbol defined in this control section Col relative address of the symbol with in this control section Col name and relative address for other external symbols.
Describe the structure of a single pass assembler. Discuss the design aspects of a two pass assembler. Describe the various stages of an assembly process and explain how they are organized in two pass assembler. What is meant by program relocation?
What is conditional assembly? Explain with example. Discuss the merits of multipass assembler. What are the basic functions of loaders. Loading — brings the object program into memory for execution Relocation — modifies the object program so that it can be loaded at an address different from the location originally specified Linking — combines two or more separate object programs and also supplies the information needed to reference them.
Define absolute loader The loader, which is used only for loading, is known as absolute loader. Bootstrap loader 3.
What is meant by bootstrap loader? This is a special type of absolute loader which loads the first program to be run by the computer. What are relative relocative loaders? Loaders that allow for program relocation are called relocating relocative loaders. What is the use of modification record? Modification record is used for program relocation. Each modification record specifies the starting address and the length of the field whose value is to be altered and also describes the modification to be performed.
What are the 2 different techniques used forrelocation? Modification record method and relocation bit method. Bit value 0 indicates no modification is required. Define bit mask The relocation bits are gathered together following the length indicator in each text record and which is called as bit mask. For e. It is used to store the name and address of the each external symbol. It also indicates in which control section the symbol is defined. It gives the beginning address in memory where the linked program is to be loaded.
The starting address is obtained from the operating system.
Perform processing of assembler directives not done during pass 1. Write the program and the assembling listing. Object code generation. Literals added to literal table.
System Software two mark questions and answers - CS2304