深入理解計(jì)算機(jī)系統(tǒng)_復(fù)習(xí)_清華(存儲(chǔ)版)
【正文】 wo Encoding ? MSB is sign bit ? exp field encodes E ? frac field encodes M Sizes ? Single precision: 8 exp bits, 23 frac bits ? Double precision: 11 exp bits, 52 frac bits ? Extended precision: 15 exp bits, 63 frac bits Floating Point Representation s exp frac “Normalized” Numeric Values Condition ? exp ? 000…0 and exp ? 111…1 Exponent coded as biased value E = Exp – Bias ?Exp : unsigned value denoted by exp ?Bias : Bias value 187。 Unsigned is dangerous! Integer C Puzzles Revisited ? x 0 ??? ((x*2) 0) ? ux = 0 ? x amp。amp。, ||, ! View 0 as ―False‖ Anything nonzero as ―True‖ Always return 0 or 1 Early termination Shift Operations ?Logical vs. Arithmetic ?Shift amount 0 or ? word size Signed vs. Unsigned in C Constants ? By default are considered to be signed integers ? Unsigned if have ―U‖ as suffix 0U, 4294967259U Casting ? Explicit casting between signed amp。 7 == 7 ??? (x30) 0 ? ux 1 ? x y ??? x y ? x * x = 0 ? x 0 amp。Single precision: 127 (Exp: 1…254, E: 126…127) 187。 movl $147,(%eax) *p = 147。 *xp = t1。 } absdiff: pushl %ebp movl %esp, %ebp movl 8(%ebp), %edx movl 12(%ebp), %eax cmpl %eax, %edx jle .L7 subl %eax, %edx movl %edx, %eax .L8: leave ret .L7: subl %edx, %eax jmp .L8 Body1 Set Up Finish Body2 pushl %ebp movl %esp, %ebp pushl %ebx movl 8(%ebp), %ecx movl 12(%ebp), %edx movl %ecx, %ebx subl %edx, %ebx movl %edx, %eax subl %ecx, %eax cmpl %edx, %ecx cmovg %ebx, %eax popl %ebx popl %ebp ret int absdiff( int x, int y) { int result。 } Goto Version Init。 Test。 loc[0] = *xp。a[i+1])。a[i], amp。 ? 2D array of data type T ? R rows, C columns ? Type T element requires K bytes Array Size ? R * C * K bytes Arrangement ? RowMajor Ordering A[0][0] A[0][C1] A[R1][0] ? ? ? ? ? ? A[R1][C1] ? ? ? ? ? ? int A[R][C]。 int result = 0。 int result = 0。 int jTnPk = k。 double v。lowest 2 bits of address must be 002 187。 } *up。 ... return ...。 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 ? Input string contains byte representation of executable code ? Overwrite return address with address of buffer ? When bar() executes ret, will jump to exploit code int bar() { char buf[64]。 int i[2]。lowest 2 bits of address must be 002 187。 } struct S1 { char c。 int result = 0。 } int var_ele (int *a, int i, int j, int n) { return a[i*n+j]。 } 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]。 operated on in floating point registers Intel GAS Bytes C Single s 4 float Double l 8 double Extended t 10/12/16 long double Array Allocation Basic Principle T A[L]。 /* Swap a[i] amp。 a[i+1] */ void swap_ele_se (long a[], int i) { swap(amp。 middle: if (Test) goto loop。 do { Body Update 。 Update ) Body Init。 } else { result = yx。 ?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 %r
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