3.2.3 Notes on Formatting

• All of the lines beginning with ‘.’ are directives to guide the assembler and linker

3.3 Data Formats

• Due to its origins as a 16-bit architecture that expanded into a 32-bit one, Intel uses the term “word” to refer to a 16-bit data type. Based on this, they refer to 32- bit quantities as “double words,” and 64-bit quantities as “quad words

 

3.4 Accessing Information

• An x86-64 central processing unit (CPU) contains a set of 16 general-purpose registers storing 64-bit values. These registers are used to store integer data as well as pointers

3.4.1 Operand Specifiers

Computer Systems GE

• ource values can be given as constants or read from registers or memory.
• he different operand possibilities can be classified into three types.
• The first type, immediate, is for constant values
• for example, $-577 or $0x1F. Different instructions allow different ranges of immediate values; the assembler will automatically select the most compact way of encoding a value
• The second type, register, denotes the contents of a register, one of the sixteen 8-, 4-, 2-, or 1-byte low-order portions of the registers for operands having 64, 32, 16, or 8 bits, respectively.
• The third type of operand is a memory reference, in which we access some memory location according to a computed address, often called the effective ad- dress.
• The most general form is shown at the bottom of the table with syntax Imm(rb,ri,s). Such a reference has four components: an immediate offset Imm, a base register rb, an index register ri, and a scale factor s, where s must be 1, 2, 4, or 8