Assembler source code file

The expressions accepted by the assembler are defined by their syntax and semantics. The following are the operators supported by the assembler:. Table shows syntactic rules, the non terminals are represented by lowercase letters, the terminal symbols are represented by uppercase letters, and the symbols enclosed in double quotes are terminal symbols.

There is no precedence assigned to the operators. You must use square brackets to establish precedence. Semantically, the expressions fall into two groups, absolute and relocatable. The equations later in this section show the legal combinations of absolute and relocatable operands for the addition and subtraction operators. All other operations are only legal on absolute-valued expressions. All numbers have the absolute attribute. Symbols used to reference storage, text, or data are relocatable.

In an assignment statement, symbols on the left side inherit their relocation attributes from the right side. In the equations below, a is an absolute-valued expression and r is a relocatable-valued expression. The resulting type of the operation is shown to the right of the equal sign. In the last example, you must declare the relocatable expressions before taking their difference. This section describes the instructions that the assembler accepts. The detailed specification of how the particular instructions operate is not included; for this, see Intel's Programmer's Reference Manual.

Instructions with two operands use the left one as the source and the right one as the destination. This is reversed from Intel's notation. Most instructions that can operate on a byte, word, or long may have b, w, or l appended to them. When an opcode is specified with no type suffix, it usually defaults to long. In general, the IA Assembler derives its type information from the opcode, where the Intel assembler can derive its type information from the operand types.

Where the type information is derived motivates the b, w, and l suffixes used in the IA Assembler. Three kinds of operands are generally available to the instructions: register , memory , and immediate. Indirect operands are available only to jump and call instructions. The assembler always assumes it is generating code for a bit segment. When bit data is called for e. Byte, word, and long registers are available on the IA processor. The names of the byte, word, and long registers available as operands and a brief description of each follow.

The segment registers are also listed. Stack segment register, the default segment register for memory operands in the stack i. General-purpose segment register; some string instructions use this extra segment as their default segment.

The assembler assumes it is generating code for a bit segment, therefore, it also assumes a bit address and automatically precedes word operations with a bit data prefix byte. All the items in the square brackets are optional, but at least one is necessary.

If you use any of the items inside the parentheses, the parentheses are mandatory. It may be any segment register. If a segment override prefix is present, you must follow it by a colon before the offset component of the address. An address must contain an offset component. It may be absolute or relocatable. A label is an example of a relocatable offset. A number is an example of an absolute offset. Its value may be 1, 2, 4, 8 to indicate the number to multiply by.

Analysis of source program statements may not be immediately followed by synthesis of equivalent target statements. This is due to forward references issue concerning memory requirements and organization of Language Processor LP. Forward reference of a program entity is a reference to the entity, which precedes its definition in the program. While processing a statement containing a forward reference, language processor does not posses all relevant information concerning referenced entity.

This creates difficulties in synthesizing the equivalent target statements. This problem can be solved by postponing the generation of target code until more information concerning the entity is available.

This also reduces memory requirements of LP and simplifies its organization. This leads to multi-pass model of language processing. It is the processing of every statement in a source program or its equivalent representation to perform language-processing function. There are three types of statements Imperative, Declarative, Assembly directives.

An imperative statement indicates an action to be performed during the execution of assembled program. Each imperative statement usually translates into one machine instruction. Declarative statement e. DS reserves areas of memory and associates names with them. DC constructs memory word containing constants. Assembler directives instruct the assembler to perform certain actions during assembly of a program, e. START directive indicates that the first word of the target program generated by assembler should be placed at memory word with address.

Tasks performed by the passes of two-pass assembler are as follows:. Synthesize the target code by processing the intermediate code generated during. It has the following fields.

OP- code : Operation code indicating the operation to be performed. Length : Length of instruction required for Location Counter Processing. Source code and script file type. The a file extension is associated with the Assembly programming language Assembler. An assembly language is a low-level language for programming computers.

It implements a symbolic representation of the numeric machine codes and other constants needed to program a particular CPU architecture. Previous file extension A file extension. Next file extension file extension A2W. Note: We try to keep all external and related links up-to-date, however we are not responsible for the content of any site linked, further links on sites linked, or any changes or updates to the the information found on these sites.