【正文】 ignment with Structures Offsets Within Structure ? Must satisfy element’s alignment requirement Overall Structure Placement ? Each structure has alignment requirement K ? Largest alignment of any element ? Initial address amp。 j n。 A+i*C*4 A+(R1)*C*4 ? ? ? Nested Array Element Access Array Elements ? A[i][j] is element of type T ? Address A + i * (C * K) + j * K = A + (i * C + j)* K ? ? ? A [i] [j] A [i] [j] ? ? ? A[i] A [R1] [0] A [R1] [C1] ? ? ? A[R1] ? ? ? A A [0] [0] A [0] [C1] ? ? ? A[0] int A[R][C]。 } swap_ele_se: movslq %esi,%rsi Sign extend i leaq (%rdi,%rsi,8), %rdi amp。 while (Test ) { Body Update 。 } else { result = yx。 movl %eax,(%edx) *p = temp。 y 0 ??? x + y 0 ? x = 0 ?? x = 0 ? x = 0 ?? x = 0 ? (x|x)31 == 1 ? ux 3 == ux/8 ? x 3 == x/8 ? x amp。 Or any other pointer BitLevel Operations in C ?Operations amp。 unsigned ux = x。x[i]。 Test。 loop: Body Update 。 ret x8664 Call using Jump ? When swap executes ret, it will return from swap_ele ? Possible since swap is a “tail call” long scount = 0。 } int get_univ_digit (int index, int dig) { return univ[index][dig]。 } { int j。lowest 3 bits of address must be 0002 ? Linux: 187。 c i[0] i[1] v sp+0 sp+4 sp+8 sp+16 sp+24 (Windows alignment) Advanced Topics ? Linux Memory Layout ? Understanding Pointers ? Buffer Overflow IA32 Linux Memory Layout Stack ? Runtime stack (8MB limit) Heap ? Dynamically allocated storage ? When call malloc(), calloc(), new() Data ? Statically allocated data ? ., arrays amp。 c i[0] i[1] v up+0 up+4 up+8 struct S1 { char c。 } *p。 for (j = 0。 A [0] [0] A [0] [C1] ? ? ? A [1] [0] A [1] [C1] ? ? ? A [R1] [0] A [R1] [C1] ? ? ?? ? ? 4*R*C Bytes ? ? ? Nested Array Row Access Row Vectors ? A[i] is array of C elements ? Each element of type T requires K bytes ? Starting address A + i * (C * K) A [i] [0] A [i] [C1] ? ? ? A[i] A [R1] [0] A [R1] [C1] ? ? ? A[R1] ? ? ? A A [0] [0] A [0] [C1] ? ? ? A[0] int A[R][C]。 scount++。 Update ) Body Init。 if (x y) { result = xy。 movl %eax,%edx temp2 = temp1。amp。, |, ~, ^ Available in C Logic Operations in C ?amp。 unsigned uy = y。 ?Computing arithmetic expressions of the form x + k*y ? k = 1, 2, 4, or 8. %rax %rdx %rcx %rbx %rsi %rdi %rsp %rbp x8664 General Purpose Registers ? Extend existing registers. Add 8 new ones. ? Make %ebp/%rbp general purpose %eax %edx %ecx %ebx %esi %edi %esp %ebp %r8 %r9 %r10 %r11 %r12 %r13 %r14 %r15 %r8d %r9d %r10d %r11d %r12d %r13d %r14d %r15d Swap in 64bit Mode ? Operands passed in registers ? First (xp) in %rdi, second (yp) in %rsi ? 64bit pointers ? No stack operations required ? 32bit data ? Data held in registers %eax and %edx ? movl operation void swap(int *xp, int *yp) { int t0 = *xp。 Update ) Body Init。 middle: if (Test) goto loop。 /* Swap a[i] amp。 } 361601656164168univcmu1 5 2 1 316 20 24 28 32 36mit0 2 1 3 936 40 44 48 52 56ucb9 4 7 2 056 60 64 68 72 7676 96 116 136 1561 5 2 0 6 1 5 2 1 3 1 5 2 1 7 1 5 2 2 1Using Nested Arrays Strengths ? C piler handles doubly subscripted arrays ? Generates very efficient code ? Avoids multiply in index putation Limitation ? Only works if have fixed array size define N 16 typedef int fix_matrix[N][N]。 int result = 0。lowest 2 bits of address must be 002 187。 strings declared in code Text ? Executable machine instructions ? Readonly Upper 2 hex digits of address BF 00 Stack Text Data Heap 08 C pointer declarations int *p p is a pointer to int int *p[13] p is an array[13] of pointer to int int *(p[13]) p is an array[13] of pointer to int int **p p is a pointer to a pointer to an int int (*p)[13] p is a pointer to an array[13] of int int *f() f is a function returning a pointer to int int (*f)() f is a pointer to a function returning int int (*(*f())[13])() f is a function returning ptr to an array[13] of pointers to functions returning int int (*(*x[3])())[5] x is an array[3] of pointers to functions returning pointers to array[5] of ints Malicious Use of Buffer Overflow ? Inpu