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Control

Control. Outline. PC-relative Address Suggested reading Chap 3.6.3. Example. jle .L2 .L5: movl % edx , % eax sarl $1, % eax subl % eax , % edx Leal (% edx , % edx , 2), % edx testl % edx , % edx jg .L5 9 .L2: 10 movl % edx , % eax.

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Control

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  1. Control

  2. Outline • PC-relative Address • Suggested reading • Chap 3.6.3

  3. Example • jle .L2 • .L5: • movl %edx, %eax • sarl $1, %eax • subl %eax, %edx • Leal (%edx, %edx, 2), %edx • testl %edx, %edx • jg .L5 9 .L2: 10 movl %edx, %eax

  4. PC-relative in the Relocatable Object • 8: 7e 0d jle 17<silly+0x17> • a: 89 d0 mov %edx, %eax dest1: 3 c: c1 f8 sar %eax • e: 29 c2 sub %eax, %edx • 10: 8d 14 52 lea (%edx, %edx, 2), %edx 6 13: 85 d2 test %edx, %edx • 15: 7f f3 jg a<silly+0x10> • 17: 89 d0 movl %edx, %eax dest2: d+a = 17 17+f3(-d) =a

  5. PC-relative in the Executable Object • 804839: 7e 0d jle 17<silly+0x17> • 804839e: 89 d0 mov %edx, %eax dest1: 3 80483a0: c1 f8 sar %eax • 80483a2: 29 c2 sub %eax, %edx • 80483a4: 8d 14 52 lea (%edx, %edx, 2), %edx 6 80483a7: 85 d2 test %edx, %edx • 80483a9: 7f f3 jg a<silly+0x10> • 80483ab: 89 d0 movl %edx, %eax dest2: d+804849e = 80483ab 80483ab+f3(-d) = 804839e

  6. Procedure Call

  7. Outline • Procedure call • Stack frame • Calling conventions • Recursive • Suggested reading • Chap 3.7

  8. Execution within Procedure/Function • Data Movement (e.g., movl $-17, (%esp)) • Arithmetic Operations (e.g., incl 8(%eax)) • Logical Operations (e.g., xorl 8(%esp), %eax) • Condition Codes (e.g., cmpl %eax, %edx) • Jump Instructions (e.g., jg .L5) How to execute cross procedures?

  9. Procedure/Function call • Another type of unconditional JUMP • SAME: • Control from one part to another • DIFF: • Return • Passing data (arguments, return values) • Local variable • Registers

  10. Basic Concept • Terminology • Caller • Callee f() call-1 g() h() call-2 • call-1 • Caller: f • Callee: g • call-2 • Caller: g • Callee: h

  11. Basic Concept • Terminology • Caller: g • Callee: f • Control Flow e.g. int g() { return 1 ; } int f() { return g() ; } int main() { g(); return f(); } g() call main() f() g() f() g()

  12. Procedure/Function Implementation • Invoke callee • Return to caller • Passing data • Registers • Local variable

  13. Procedure/Function Implementation • Invoke callee: call (new instructions) • Return to caller • Passing data • Registers • Local variable

  14. Invoke Callee • Instruction • call label (direct) • call *operand(indirect) • Behavior description (by hardware) • Save return address in the stack • Jump to the entryof callee call = push + jmp • push retaddr • jmpcallee

  15. Execution of call and ret //beginning of function sum • 08048394 <sum>: • 8048394: 55 push %ebp . . . • 80483a4: ret . . . //call to sum from main • 80483dc: e8 b3 ffffff call 8048394<sum> • 80483e1: 83 c4 14 add $0x14, %esp Executing call After call

  16. Procedure/Function Implementation • Invoke callee: call (new instructions) • Return to caller: ret (new instructions) • Passing data • Registers • Local variable

  17. Return to Caller • Instruction • ret • Behavior description (by hardware) • Pop return address from stack • Jump to return addressin caller ret = pop + jmp • pop retaddr • jmpretaddr

  18. Execution of call and ret //beginning of function sum • 08048394 <sum>: • 8048394: 55 push %ebp . . . • 80483a4: ret . . . //call to sum from main • 80483dc: e8 b3 ffffff call 8048394<sum> • 80483e1: 83 c4 14 add $0x14, %esp executing ret After ret

  19. Procedure/Function Implementation • Invoke callee: call (new instructions) • Return to caller: ret (new instructions) • Passing data: stack, register • Registers • Local variable

  20. %ebp %esp Stack Frame Structure • The portion of stack allocated for a procedure • A stack frame is delimited by • The frame pointer %ebp • The stack pointer %esp • The stack pointer can move when the procedure is executing (dynamic) • The frame pointer is static

  21. %ebp %esp Stack Frame Structure • call: save return address in the stack • ret: pop return address from stack • The end of caller’s stack frame

  22. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe %ebp %esp

  23. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe • Frames are chained • 1. call callee %ebp %esp

  24. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe • Frames are chained • 1. call callee • callee: • 2. push %ebp • 3. mov %esp, %ebp %ebp %esp

  25. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe • Frames are chained • 1. call callee • callee: • 2. push %ebp • 3. mov %esp, %ebp %ebp %esp

  26. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe • Frames are chained • 1. call callee • callee: • 2. push %ebp • 3. mov %esp, %ebp %ebp %esp

  27. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe • Frames are chained • 1. call callee • callee: • 2. push %ebp • 3. mov %esp, %ebp • . . . • n-2. mov %ebp, %esp • n-1. pop %ebp • n. ret %ebp %esp

  28. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe • Frames are chained • 1. call callee • callee: • 2. push %ebp • 3. mov %esp, %ebp • . . . • n-2. mov %ebp, %esp • n-1. pop %ebp • n. ret %ebp %esp

  29. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe • Frames are chained • 1. call callee • callee: • 2. push %ebp • 3. mov %esp, %ebp • . . . • n-2. mov %ebp, %esp • n-1. pop %ebp • n. ret %ebp %esp

  30. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe • Frames are chained • 1. call callee • callee: • 2. push %ebp • 3. mov %esp, %ebp • . . . • n-2. mov %ebp, %esp • n-1. pop %ebp • n. ret %ebp %esp

  31. Frame Chain • Pointers (%ebp/%esp) only delimit topmostframe • Frames are chained %ebp %esp

  32. Restore Caller %ebp • Instruction • leave • Behavior description (by hardware) • Adjust %esp to callee %ebp • Pop caller %ebp from stack leave = mov + pop • mov %ebp, %esp • pop %ebp

  33. Execution of call and ret //beginning of function sum • 08048394 <sum>: • 8048394: 55 push %ebp . . . • 80483a4: ret . . . //call to sum from main • 80483dc: e8 b3 ffffff call 8048394<sum> • 80483e1: 83 c4 14 add $0x14, %esp Executing call After call After ret

  34. Memory Layout User stack

  35. %ebp %esp Passing Data: Arguments • Pushed by Caller • Saved in caller frame • Just upon of return address • From Nth to 1st (from right to left) • Used by Callee • Relative to %ebp • Offset: 4 + 4*i + %ebp

  36. %ebp %esp Passing Data: Arguments push argument N

  37. %ebp %esp Passing Data: Arguments push argument N . . . push argument 1

  38. %ebp %esp Passing Data: Arguments push argument N . . . push argument 1 call callee

  39. %ebp %esp Passing Data: Arguments push argument N . . . push argument 1 call callee push %ebp

  40. %esp / %ebp Passing Data: Arguments push argument N . . . push argument 1 call callee push %ebp mov %esp, %ebp . . .

  41. Passing Data: Return Value • Specific register to keep the return value • %eax is used to pass the result of callee to caller

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