security study guide

, double Int→float will not overflow but may be roundedInt/float→double results retain exact valuesDouble→float may overflow to ±∞ and may be rounded due to small accuracyThe float/double→int rounds to 0 and can overflow.Problems encountered:1. Error in compiling the 28-page code in the bookCheck the code seems to be nothing wrong, do not know why ... at last, I commented out the line . The source code is as follows2. Exercise 2.52 do not understand, I hope the teacher can explain in classI

-point numbers，权重是2 的E次幂。Case 1: Normalized value. When exp is not full modulus is 1 or 0. The Order field is interpreted as a biased representation of a signed integer.Case 2: Non-normalized value: When the Order field is full 0 o'clock, the number represented is a non-normalized form. In this case, the order value is E = 1-bias, and the value of the mantissa is M = f, which is the value of the small number field, which does not contain the implied beginning of 1Case 3: Special Value: The Order

: Is where the last keyword is located.Space (SPACEBAR): Page turn.Enter: Scrolls down one line.J,k (Vim Editor's move key): Scrolls forward backward by one line.H key: Displays use Help (because man uses less as a reader, which is actually the help of the less tool).Q: Exit.Info command: Get more help, but it's usually enough to use man.--help: If you know the purpose of a command, just want to quickly see some of its specific parameters.4. HomeworkOperation Steps:Results:(The '-W ' parameter s

scoped than the custom variable, such as the shell environment variables acting on itself and its child process. In all Unix and Unix-like systems, each process has its own set of environment variables, and by default, when a process is created, it is explicitly specified in the process creation, and it inherits most of the environment settings of its parent process. The shell program also runs on the operating system as a process, and most of the commands we run in the shell will run as a chil

overlap. If one of the execution trajectories happens to reach the deadlock state D then there is no further progress, since overlapping blocks block progress in each legal direction. In other words, the program is deadlocked because each thread waits for a V operation that is not possible at all.Deadlock is a rather difficult problem because it is not always predictable. Some lucky lines of execution will bypass the deadlock area, while others will fall into the area.20135210 Ellis--The basic

frees the allocated blocks that the program no longer needs, called garbage , and the process of automatically reclaiming heap storage is called garbage collection . The garbage collector periodically identifies the garbage blocks and calls free accordingly, putting the blocks back into the idle listSecond, the garbage collector sees the memory as a forward-reaching graph, only when there is a path from any root node to reach p, it is said that node p is reachable, and the unreachable point is

that is a member of the size class.This method is fast and efficient for memory use.3. Partner Systems　　Each of these size classes is a power of 2Thus, given the size of the address and block, it is easy to calculate the address of its partner, that is to say: The address of a block and its partner's address only a different.Pros: Quick Search, quick merge.9.10 Garbage CollectionThe garbage collector is a dynamic storage allocator that automatically frees the allocated blocks that the program n

information is accessed relative to the frame pointer. Program register groups are the only resources that can be shared by all processes. 根据惯例寄存器%eax,%edx,%ecx被划分为调用者保存寄存器。 %ebx,%esi,%edi被划分为被调用者保存寄存器。 %ebp,%esp 惯例保持 %eax用来保存返回值 The call command has a target, which indicates the address of the instruction at the beginning of the called process, and the effect is to put the return address into the stack and jump to the beginning of the called procedure. The RET instruction pop

, such as read, are stopped in the Read function, and so on, the Read function is finished, in fact, the control is no longer in main, but through the read function to jump to the kernel. Also such as the signal, the process receives the signal, the trigger control jumps to the signal processing program.This is also true of the non-local jump that is now spoken. The control jumped away. The user-level exception control flow form, called a non-local jump, transfers control directly from one

manipulating processes:STRACE：打印一个正在运行的程序和它的子进程调用的每个系统调用的轨迹。对于好奇的的工具。用-StatiC编译你的程序，能传到一个更干净的、不带学生而言，这是一个令人着迷有大量与共享库相关的输出的轨迹。PS：列出当前系统中的进程（包括僵死进程）TOP：打印出关于当前进程资源使用的信息。PMAP：显示进程的存储器映射。proc:一个虚拟文件系统，以ASCII文本格式输出大量内核数数据结构的内容，用户程序可 cat 2 / proc / load avg” , 观察在Linux系统上的平均负载。SummarizeThis week to learn more content, the front also read more understand, behind some chaos, I hope the teacher in class to talk about non-local jump knowledge, I still do not understand here.ResourcesTextbook: "In-depth u

flow is called a time slice. So multitasking is also called time slicing.A processor typically provides this functionality with a pattern bit in a control register that describes the privileges currently enjoyed by the process. When a pattern bit is set, the process runs in kernel mode (sometimes called Super User mode).When no mode bit is set, the process runs in user mode. A process in user mode does not allow the execution of privileged directives. It also does not allow processes in user mo

Learning tasks1. Read the textbook and complete the After-school practice (the book has a reference answer)3.1-3.7 in practice, Focus: 3.1,3.3,3.5,3.6,3.9,3.14,3.15,3.16,3.22,3.23,3.27,3.29,3.30,3.33,3.342. Examination: Exercises to change the data3. Experiment: Need to practice in the lab building4. Deepening, practical topics, extra pointsLearning process3.1 Historical view (textbook p103-p105)1978 8086 29K transistors to 2008 Corei7 781M transistors (38% per annum, doubling every 26 months)3.

control to the beginning of a function, and the RET instruction returns to the next instruction after the call instruction.stack frame of gdb command:BACKTRACE/BT Nn is a positive integer that represents only the stack information for the top n-tier of the stack.The-n table is a negative integer that prints only the stack information for the n-tier below the stack.Frame nN is an integer starting from 0, which is the layer number in the stack. For example: Frame 0, representing the top of the st

program uses a program stack to support procedure calls. The machine uses stacks to pass process parameters, store return information, save registers, and local storage. 2. Translation control (1) Call command The target is the address of the instruction that indicates the start of the called process The effect is to put the return address into the stack and jump to the beginning of the called procedure. (2) RET instruction POPs the address from the stack and

fast.The minimum number of cache misses is within each loop.2. Repeated references to local variables are good because the compiler is able to cache them in a register file (temporal locality).3. The reference pattern of step 1 is good because the cache at all levels in the memory hierarchy is storing the data as contiguous blocks (spatial locality).Reference: 1. "In-depth understanding of computer Systems", chapter sixth2. Experimental building course-in-depth understanding of computer system

s=2^s cache groups, each containing an e cache line, each row consists of a b=2^b byte block, a valid bit (indicating whether the row contains valid information), t=m-(B+s) Tag bits, which uniquely identify blocks stored in this cache line The cache determines whether a request is hit and then jerks the process of the requested word, divided into: Group selection, line matching, word extraction Group selection: Extracts the group index from the address of W, which is interpre

, which are placed in a sealed package.The entire device is often referred to as a disk drive, referred to as disk.Cylinder: The set of tracks that are equal to the center of the spindle on all disc surfaces.2. Disk capacityRecording density: The number of digits that can be placed in the segment of each inch of the trackTrack density: The number of tracks that can be in an inch from the center of the discSurface density: The product of recording density and track densityDisk Capacity: (bytes/se

recently referenced data items, or to the data item itself that has recently been referenced. This tendency, called the principle of locality, is a persistent concept(1) Time locality: In a program with good time locality, the memory location that has been quoted once is likely to be referenced more than once in the near future(2) Spatial locality: In a program with good spatial locality, if a memory location is referenced once, then the program is likely to refer to a nearby memory location in

double. On machines that support IEEE floating-point format, these data types correspond to single-precision and double-precision floating-point.The newer version of the C language, including the ISO C99, contains the third floating-point data type long double. For many machines and compilers, this data type is equivalent to a double data type. However, for Intel compatible machines, GCC uses the 80-bit "extended precision" format to implement this data type, providing a much larger range and p

Perform the default action Ignore signal Capture signal: Perform signal processing function, switch to user state. Snapping: Signal functionsIgnore signal: sig_ignDefault action: SIG_DFL(3) Multi-signal processingProcessing method:1. Recursive, call the same handler function2. Ignoring a second signal3. Block the second signal until the first one is processedSixth section non-local jumpThe C language, the user-level exception control flow form, is provided through the setj