Stack Frame Components. Using the Stack (4) Stack Structure. Updated Stack Structure. Caller Frame Arguments 7+ Return Addr Old %rbp

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$+ Local Variables rgument Build 1 Using the Stack (4) Stack Structure long call_incr() { long v1 = 15213; long v2 =$ incr(&v1, 3000); return v1+v2; Rtn address 18213 Unused +8 call_incr: subq $16, movq $15213, 8() movl $3000, %esi

incr(&v1, 3000); return v1+v2; Rtn address 18213 Unused +8 call_incr: subq $16, movq $15213, 8() movl $3000, %esi

1 Stack Frame Components Frame pointer %rbp Stack pointer Caller Frame rguments 7+ Return ddr Old %rbp Saved Registers + Local Variables rgument Build 1 Using the Stack (4) Stack Structure long call_incr() { long v1 = 15213; long v2 = incr(&v1, 3000); return v1+v2; Rtn address Unused +8 call_incr: subq $16, movq $15213, 8() movl $3000, %esi leaq 8(), %rdi call incr addq 8(), %rax addq $16, ret Register Use(s) %rax Return value Updated Stack Structure Rtn address 2

2 Stack Frame Components Frame pointer %rbp Stack pointer Caller Frame rguments 7+ Return ddr Old %rbp Saved Registers + Local Variables rgument Build 3 Register Conventions Return value (caller-saved) rguments (caller-saved) Caller-saved temporaries %rax %rdi %rsi %rdx %rcx %r8 %r9 %r10 %r11 Callee-saved Temporaries Special %rbx %r12 %r13 %r14 %r15 %rbp 4

3 Callee-Saved Example (1) long call_incr2(long x) { long v1 = 15213; long v2 = incr(&v1, 3000); return x+v2; call_incr2: subq $16, movq $15213, 8() movl $3000, %esi leaq 8(), %rdi call incr addq $16, ret Ini$al Stack Structure Rtn address Resul$ng Stack Structure Rtn address Saved %rbx Unused 5 Callee-Saved Example (2) Resul3ng Stack Structure long call_incr2(long x) { long v1 = 15213; long v2 = incr(&v1, 3000); return x+v2; call_incr2: subq $16, movq $15213, 8() movl $3000, %esi leaq 8(), %rdi call incr addq $16, ret Rtn address Saved %rbx Unused Pre-return Stack Structure Rtn address 6

4 Stack Frame Components Frame pointer %rbp Stack pointer Caller Frame rguments 7+ Return ddr Old %rbp Saved Registers + Local Variables rgument Build 7 Recursion Example 8

5 Recursion Base Case %rdi x rgument %rax Return value Return value 9 Recursion Register Save %rdi x rgument Rtn address Saved %rbx 10

6 Recursion Call Setup %rdi x >> 1 Rec. argument %rbx x & 1 Callee-saved 11 Recursive Call %rbx x & 1 Callee-saved %rax Recursive call return value 12

7 Recursion Result %rbx x & 1 Callee-saved %rax Return value 13 Recursion Result %rax Return value Return value 14

8 rray llocation char string[12]; x x + 12 int val[5]; x x + 4 x + 8 x + 12 x + 16 x + 20 double a[3]; x x + 8 x + 16 x + 24 char* p[3]; x x + 8 x + 16 x rray ccess int get_val(int a[], int i) { return a[i]; # %rdi = a # %rsi = i movl (%rdi,%rsi,4), %eax # a[i] 16

9 rray Looping void inc5(int a[]) { size_t i; for (i = 0; i < 5; i++) a[i]++; # %rdi = a # i = 0 jmp.l3 # goto middle.l4: # loop: addl $1, (%rdi,%rax,4) # a[i]++ addq $1, %rax # i++.l3: # middle cmpq $4, %rax # i:4 jbe.l4 # if <=, goto loop 17 Multi-Level rray int* zips[3]; zips[0] = (int*) malloc(sizeof(int)*5); zips zips[1] zips[0] zips[2]

10 Multi-Level rray Example zips zips[1] zips[0] zips[2] int get_zip_digit (size_t index, size_t digit) { return zips[index][digit]; salq $2, %rsi # 4*digit addq 160(,%rdi,8), %rsi # p = zips[index] + 4*digit movl (%rsi), %eax # return *p ret 19 Nested rray int [R][C]; [0] [0] [0] [C-1] [1] [0] [1] [C-1] [R-1] [0] [R-1] [C-1] 4*R*C Bytes 20

11 Nested rray Example int zips[4][5]; int* get_zip(int index) { return zips[index]; # %rdi = index leaq (%rdi,%rdi,4),%rax # 5 * index leaq 76(,%rax,4),%rax # zips + (20 * index) 21

Machine-level Programs Procedure

Computer Systems Machine-level Programs Procedure Han, Hwansoo Mechanisms in Procedures Passing control To beginning of procedure code Back to return point Passing data Procedure arguments Return value