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The x86 Instruction Set

The x86 Instruction Set. Lecture 17 Fri, Mar 19, 2004. The Instruction Set. A table of x86 instructions: http://www.jegerlehner.ch/intel/IntelCodeTable.pdf. The Runtime Stack. The runtime stack is a portion of memory that used as a stack during program execution.

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The x86 Instruction Set

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  1. The x86 Instruction Set Lecture 17 Fri, Mar 19, 2004

  2. The Instruction Set • A table of x86 instructions: http://www.jegerlehner.ch/intel/IntelCodeTable.pdf

  3. The Runtime Stack • The runtime stack is a portion of memory that used as a stack during program execution. • The address of the top of the stack is stored in the register esp, called the stack pointer. • The stack grows in a “downward” direction. • When values are pushed, esp is decremented. • When values are popped, esp is incremented.

  4. The Runtime Stack • esp points to the “top” of the stack. Stack esp

  5. The Runtime Stack • Push a value and decrement esp. Stack esp

  6. The Runtime Stack • Push another value and decrement esp again. Stack esp

  7. The Runtime Stack • Pop a value and increment esp. Stack esp

  8. The Runtime Stack • Pop another value and increment esp again. Stack esp

  9. The Push and Pop Instructions • The push and pop instructions have the format push source pop destination • source is a register, a memory address, or an immediate value. • destination is a register or a memory address.

  10. The Push and Pop Instructions • The push instruction will decrement the stack pointer and then move source to the stack. • The pop instruction will move the value on the stack to destination and then increment the stack pointer.

  11. Processing the Syntax Tree • The syntax tree is processed in a post-order traversal. • At each node • Process the left subtree. • Process the right subtree. • Process the node.

  12. Using the Stack • As each node of the syntax tree is executed, it will leave its result on the run-time stack. • The next node will pop that result off the stack (if it needs it) and then push its own result onto the stack, and so on.

  13. ASSIGN NAME a MINUS PLUS NUM 5 DEREF DEREF NAME b NAME c Example • The syntax tree for a = b + c – 5 is

  14. Example • Order of execution • NAME – Push the address of a. • NAME – Push the address of b. • DEREF – Push the value of b. • NAME – Push the address of c. • DEREF – Push the value of c. • PLUS – Pop two values, add them, push the result. • NUM – Push 5. • MINUS – Pop two values, subtract them, push the result. • ASSIGN – Pop the value and the address, store the value at the address, push the result.

  15. A NUM Node • A NUM node loads the integer whose value is stored in the node. • For example, to load 5: push $5 • The $ sign means the “immediate” value 5.

  16. A NAME Node • A NAME node pushes the address of the name that is stored in the node. • For example, to push the address a: lea a,%eax push %eax • The instruction “push a,” would push the value at memory address a onto the stack, which is not what we want.

  17. A DEREF Node • A DEREF node expects to find a memory address on top of the stack. • It pushes the value stored at that address. pop %eax push (%eax) • The parentheses mean “the value at the address in the register.” • This is the indirect addressing mode.

  18. The Add Instruction • The add instruction has the format add source,destination • The value at source is added to the value at destination and the result is stored at destination. • source is a register, a memory address, or an immediate value. • destination is a register or a memory address.

  19. A PLUS Node • A PLUS node expects to find two numbers on the stack. • The right operand should be on top. • It pops the values, adds them, and pushes the result. pop %edx pop %eax add %edx,%eax push %eax

  20. An ASSIGN Node • An ASSIGN node expects to find an address and a value on the stack. • The value should be on top. • It pops the value and the address, stores the value at the address, and pushes the value. pop %eax pop %edx mov %eax,(%edx) push %eax

  21. The imul Instruction • The imul instruction performs multiplication of signed integers. • The first format imul source • source is one operand. • eax is the other operand. • The destination is edx:eax, which holds a 64-bit value.

  22. The imul Instruction • The second format imul register,source • source is one operand. • It is a register, a memory address, or an immediate value. • register is the other operand and the destination.

  23. The imul Instruction • The third format imul register,source,immediate • register is the destination. • source is one operand. • It is a register, a memory address, or an immediate value. • immediate is the other operand.

  24. A TIMES Node • A TIMES node expects to find two values on the stack. • It pops them, multiplies them, and pushes the result. pop %eax pop %ecx imul %ecx push %eax

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