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title TARGET DECK FILE TAGS tags
Instructions Obsidian::STEM x86-64
x86-64

Overview

x86-64 instructions are designed so that commonly used instructions and those with fewer operands are encoded in a smaller number of bytes. Instructions range in length from 1 to 15 bytes.

x86-64 assembly comes in two flavors: ATT and Intel. ATT is most common in Linux systems so I focus on that. The most important distinction between the two is operand ordering: Intel syntax lists multiple operands in reverse order compared to ATT.

%%ANKI Basic x86-64 assembly comes in what two formats? Back: ATT and Intel. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic Which x86-64 assembly format does Linux use? Back: ATT. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic Which x86-64 assembly format does Microsoft use? Back: Intel. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the "most confusing" difference between ATT and Intel assembly? Back: Multiple operands in one are listed in reverse order relative to the other. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

Instruction Classes

There are three types of operands:

  • Immediates. These denote constant values. In ATT assembly, they are written with a $ followed by an integer using standard C notation.
  • Registers. These denote the contents of a register.
  • Memory. These denote some memory location according to a computed address (i.e. the effective address).
Type Form Operand Value Name
Immediate \textdollar Imm Imm Immediate
Register r_a R[r_a] Register
Memory Imm M[Imm] Absolute
Memory (r_a) M[R[r_a]] Indirect
Memory Imm(r_b) M[Imm + R[r_b]] Base + displacement
Memory (r_b, r_i) M[R[r_b] + R[r_i]] Indexed
Memory Imm(r_b, r_i) M[Imm + R[r_b] + R[r_i]] Indexed
Memory (,r_i,s) M[R[r_i] \cdot s] Scaled indexed
Memory Imm(,r_i,s) M[Imm + R[r_i] \cdot s] Scaled indexed
Memory (r_b,r_i,s) M[R[r_b] + R[r_i] \cdot s] Scaled indexed
Memory Imm(r_b,r_i,s) M[Imm + R[r_b] + R[r_i] \cdot s] Scaled indexed

%%ANKI Basic What are the types of source operands instructions can specify? Back: Immediates, registers, and memory addresses. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What are the types of destination operands instructions can specify? Back: Registers and memory addresses. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What does an immediate operand denote? Back: A constant value. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic In ATT syntax, how is an immediate written? Back: As a $$ followed by an integer using standard C notation. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic In ATT syntax, how is a register written? Back: As a % followed by the name of the register. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form \textdollar Imm? Back: Imm Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form r_a? Back: R[r_a] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form Imm? Back: M[Imm] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form (r_a)? Back: M[R[r_a]] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form Imm(r_b)? Back: M[Imm + R[r_b]] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form (r_b, r_i)? Back: M[R[r_b] + R[r_i]] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form Imm(r_b, r_i)? Back: M[Imm + R[r_b] + R[r_i]] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form (,r_i,s)? Back: M[R[r_i] \cdot s] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form Imm(,r_i,s)? Back: M[Imm + R[r_i] \cdot s] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form (r_b,r_i,s)? Back: M[R[r_b] + R[r_i] \cdot s] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the operand value of form Imm(r_b,r_i,s)? Back: M[Imm + R[r_b] + R[r_i] \cdot s] Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What distinguishes operand value r_a from (r_a)? Back: The former denotes the register value. The latter denotes the value in memory at the address stored in r_a. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What values can s take on in operand form Imm(r_b,r_i,s)? Back: 1, 2, 4, or 8. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What operand form is named "immediate"? Back: \textdollar Imm Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What operand form is named "register"? Back: r_a Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What operand form is named "absolute"? Back: Imm Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What operand form is named "indirect"? Back: (r_a) Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What operand form is named "base + displacement"? Back: Imm(r_b) Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the most general operand form named "indexed" (not "scaled indexed")? Back: Imm(r_b, r_i) Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the most general operand form named "scaled indexed" (not indexed)? Back: Imm(r_b, r_i, s) Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic Consider scaled index operand form Imm(r_b, r_i, s). What values can r_b take on? Back: Any 64-bit register. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic Consider scaled index operand form Imm(r_b, r_i, s). What values can r_i take on? Back: Any 64-bit register. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic Consider scaled index operand form Imm(r_b, r_i, s). What values can s take on? Back: 1, 2, 4, or 8. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

Bibliography

  • Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.