【编译连接】 as -g --32 -o hello.o hello.s ld -m elf_i386 -o hello hello.o linux下的这个文件下有很多汇编的包含目录，比如unistd_32.h文件里面定义了所有的系统调用号对应的常量 /usr/include/asm 【指令】 addl subl imull 计算结果一般存在第二个参数中 decl incl pushl popl do pushl , %esp gets subtracted by 4 so that it points to the new top of the stack movl movb call ret je jg jge jl jle jmp shrl 向右移动 directive .section .lcomm 声明一个.bss段的变量 .lcomm my_buffer, 500 .equ allows you to assign names to numbers .equ LINUX_SYSCALL, 0x80 .include .globl read_record .type read_record, @function .rept .ascii "Fredrick\0" .rept 31 #Padding to 40 bytes .byte 0 .endr Table of Contents 1 Introduction Welcome to Programming Your Tools 2 Computer Architecture Structure of Computer Memory The CPU Some Terms Interpreting Memory Data Accessing Methods immediate mode movl $1, %eax $1代表数字1 register addressing mode direct addressing mode movl 1, %eax 把地址1的值移到%eax movl ADDRESS, %eax 把ADDRESS地址的值移到%eax中 indexed addressing mode multiplier movl BEGINNINGADDRESS(,%INDEXREGISTER,WORDSIZE) movl string_start(,%ecx,1), %eax indirect addressing mode base pointer addressing mode 3 Your First Programs Entering in the Program Outline of an Assembly Language Program general-purpose registers • %eax • %ebx • %ecx • %edx • %edi 可能是data idex的缩写 • %esi 变址寄存器是指寄存器ESI、EDI、SI和DI的寄存器，它们主要用于存放存储单元在段内的偏移量 %cl first part of %ecx special-purpose • %ebp the current base pointer register • %esp the stack register, %esp , always contains a pointer to the current top of the stack • %eip the instruction point • %eflags the status register，别的指令执行完的状态码会存在这里面 e代表extend，为了跟之前的16位的寄存器区别，64位寄存器以r开头 寄存器通常会作为指令的参数 Planning the Program Finding a Maximum Value jump je jg jge jl jle jmp Addressing Modes general form ADDRESS_OR_OFFSET(%BASE_OR_OFFSET,%INDEX,MULTIPLIER) FINAL ADDRESS = ADDRESS_OR_OFFSET + %BASE_OR_OFFSET + MULTIPLIER * %INDEX direct addressing mode movl ADDRESS, %eax indexed addressing mode movl string_start(,%ecx,1), %eax 如果%ecx的值是2的话，那就是 access the third one， 因为计数是从0开始 indirect addressing mode movl (%eax), %ebx 把%eax的地址的值移到%ebx base pointer addressing mode movl 4(%eax), %ebx %eax地址加4然后取地址 immediate mode movl $12, %eax $12代表数字12 movl $my_buffer, %ecx $my_buffer代表my_buffer的地址 register addressing mode movl %eax, %ebx 4 All About Functions Dealing with Complexity How Functions Work Assembly-Language Functions using the C Calling Convention 1.pushes all of the parameters onto the stack in the reverse order 2.issues a call instruction pushes the address of the next instruction onto the stack modifies the instruction pointer (%eip) to point to the start of the function 3.the function itself has some work to do pushl %ebp # 把调用者的栈帧底部地址保存起来 movl %esp, %ebp # 把调用者的栈帧顶部地址, 设置为本栈帧的底部，for access the parameters from the base pointer. subl $8, %esp the function reserves space on the stack for any local variables 局部变量有指针，寄存器不会有指针的 4.When a function is done executing stores it’s return value in %eax resets the frame stack. 即reset %esp %ebp use ret. It returns control back to wherever it was called from movl %ebp, %esp popl %ebp ret This pops the top value(return address) off of the stack, and then jumps to it. 5.after call deal return value, return values are always stored in %eax clean up your stack parameters after a function call returns. addl $8, %esp #move the stack pointer back 如果调用的时候有参数的话要恢复栈 stack layout Parameter #N <--- N*4+4(%ebp) ... Parameter 2 <--- 12(%ebp) Parameter 1 <--- 8(%ebp) Return Address <--- 4(%ebp) Old %ebp <--- (%ebp) Local Variable 1 <--- -4(%ebp) Local Variable 2 <--- -8(%ebp) and (%esp) argument nums 8(%esp) program name 12(%esp) first agrs 16(%esp) A Function Example Recursive Functions 5 Dealing with Files The UNIX File Concept Buffers and bss .text .data .bss Standard and Special Files Using Files in a Program The number of arguments is stored at 8(%esp) , the name of the program is stored at 12(%esp) , and the arguments are stored from 16(%esp) on. 6 Reading and Writing Simple Records Writing Records Reading Records Modifying the Records 7 Developing Robust Programs Where Does the Time Go? Some Tips for Developing Robust Programs Handling Errors Effectively Making Our Program More Robust 8 Sharing Functions with Code Libraries Using a Shared Library 编译指令 as helloworld-lib.s -o helloworld-lib.o ld -dynamic-linker /lib/ld-linux.so.2 -o helloworld-lib helloworld-lib.o -lc How Shared Libraries Work ldd ./helloworld-lib show all dynamic lib Finding Information about Libraries Most of your system libraries are in /usr/lib or /lib Useful Functions Building a Shared Library 9 Intermediate Memory Topics How a Computer Views Memory The Memory Layout of a Linux Program environment variables ... command-line arguments 2 command-line arguments 1 program name the number of arguments <--%esp .bss .data .text Every Memory Address is a Lie Earlier we talked about the inaccessible memory between the .bss and the stack, but we didn’t talk about why it was there. The reason is that this region of virtual memory addresses hasn’t been mapped onto physical memory addresses. in order to make the process more efficient, memory is separated out into groups called pages. you should try to keep most memory accesses within the same basic range of memory, so you will only need a page or two of memory at a time Getting More Memory brk A Simple Memory Manager The allocate_init function The allocate function The deallocate function Performance Issues and Other Problems 1.每次都要循环一遍 2.当内存满时，循环每个块的内存时，都要从disk中load出来去检查是否可用 3.brk的系统调用的次数 They aren’t like functions, because the processor has to switch modes. 4.空间浪费 Using our Allocator More Information 10 Counting Like a Computer Counting Counting Like a Human Counting Like a Computer Conversions Between Binary and Decimal Truth, Falsehood, and Binary Numbers boolean operators：AND OR NOT XOR These operations are useful for two reasons: • The computer can do them extremely fast • You can use them to compare many truth values at the same time xorl %eax, %eax 等价于 movl $0, %eax XOR的意义：判断两个数的位不同，不同的用1表示 Shift left 10010111 = 00101110 Rotate left 10010111 = 00101111 左边的移到右边 The Program Status Register carry flag 两个register相加溢出了会设置成这个flag Other Numbering Systems Floating-point Numbers Negative Numbers 首位表示符号的问题 1.电路设计更复杂 2.会出现两个0，一个正的0和一个负的0。比较的时候就会出问题 two’s complement representation(二进制补码) 1. Perform a NOT operation on the number 2. Add one to the resulting number 特殊处： 首位0为正数，1为负数 0在二进制补码中视为正数 把32位的负数转换成64位的时候，左边的要用符号位填上 x86 processor有一些指令是根据符号不同而不同的 Octal and Hexadecimal Numbers 0x 0b Order of Bytes in a Word The x86 processor is a little-endian processor 当从寄存器写到内存的时候需要转换成大端 Converting Numbers for Display 11 High-Level Languages Compiled and Interpreted Languages Your First C Program Perl Python 12 Optimization When to Optimize Optimization is not necessary during early development When you optimize, your code generally becomes less clear, because it becomes more complex Where to Optimize running a profiler to determine which function is cost most Local Optimizations(微观层面，比如代码片段上) Global Optimization(宏观层面，比如架构上) 13 Moving On from Here From the Bottom Up From the Top Down From the Middle Out Specialized Topics Further Resources on Assembly Language Appendix A GUI Programming B Common x86 Instructions C Important System Calls D Table of ASCII Codes E C Idioms in Assembly Language F Using the GDB Debugger G Document History H GNU Free Documentation License I Personal Dedication