《Programming from the Ground Up》阅读笔记：p88-p94

《Programming from the Ground Up》学习第5天，p88-p94总结，总计7页。

一、技术总结

1.touppercase.s

#PURPOSE: This program converts an input file 
#to an output file with all letters 
#converted to uppercase.

#PROCESSING:
#(1)Open the input file
#(2)Open the output file
#(3)While we're not at the end of the input file
#  (a)read part of file into our memory buffer
#  (b)go throught each byte of memory, if the byte is a lower-case letter, convert it to uppercase
#  (c)write the memory buffer to output file

 .section .data

#######CONSTANTS#######

 #system call numbers
 .equ SYS_OPEN, 5
 .equ SYS_WRITE, 4
 .equ SYS_READ, 3
 .equ SYS_CLOSE, 6
 .equ SYS_EXIT, 1
 
 #options for open (look at
 #/usr/incude/asm/fcntl.h for
 #various values. You can combine them
 #by adding them or ORing them)
 #This is discussed at greater length
 #in "Counting Like a Computer"
 .equ O_RDONLY, 0
 .equ O_CREAT_WRONLY_TRUNC, 03101
 
 #standard file descriptors
 .equ STDIN, 0
 .equ STDOUT, 1
 .equ STDERR, 2
 
 #system call interrupt
 .equ LINUX_SYSCALL, 0X80
 
 .equ END_OF_FILE, 0 #This is the return value 
                     #of read which means we've
                     #hit the end of the file
 
 .equ NUMBER_ARGUMENTS, 2

.section .bss
 #Buffer - This is where the data is loaded into 
 #from the data file and written from 
 #into the output file. This should 
 #never exceed 16000 for various
 #reasons.
 
 .equ BUFFER_SIZE, 500
 .lcomm BUFFER_DATA, BUFFER_SIZE
 
 .section .text
 
 #STACK POSITIONS
 .equ ST_SIZE_RESERVE, 8
 .equ ST_FD_IN, -4
 .equ ST_FD_OUT, -8
 .equ ST_ARGC, 0 #Number of arguments
 .equ ST_ARGV_0, 4 #Name of program
 .equ ST_ARGV_1, 8 #Input file name
 .equ ST_ARGV_2, 12 #Output file name

 .globl _start
_start:
 ###INITIALIZE PROGRAM###
 #save the stack pointer

 mov %rsp, %rbp
 
 #Allocate space for our file descriptors
 #on the stack
 sub $ST_SIZE_RESERVE, %rsp

open_files:
open_fd_in:
 ###OPEN INPUT FILE###
 #open syscall
 mov $SYS_OPEN, %rax
 #input filename into %rbx
 mov ST_ARGV_1(%rbp), %rbx
 #read-only flag
 mov $O_RDONLY, %rcx
 #this doesn’t really matter for reading
 mov $0666, %rdx
 #call Linux
 int $LINUX_SYSCALL

store_fd_in:
 #save the given file descriptor
 mov %rax, ST_FD_IN(%rbp)
 
open_fd_out:
 ###OPEN OUTPUT FILE###
 #open the file
 mov $SYS_OPEN, %rax
 #output filename into %rbx
 mov ST_ARGV_2(%rbp), %rbx
 #flags for writing to the file
 mov $O_CREAT_WRONLY_TRUNC, %rcx
 #mode for new file (if it’s created)
 mov $0666, %rdx
 #call Linux
 int $LINUX_SYSCALL
 
store_fd_out:
 #store the file descriptor here
 mov %rax, ST_FD_OUT(%rbp)
 
 ###BEGIN MAIN LOOP###
read_loop_begin:

 ###READ IN A BLOCK FROM THE INPUT FILE###
 mov $SYS_READ, %rax
 #get the input file descriptor
 mov ST_FD_IN(%rbp), %rbx
 #the location to read into
 mov $BUFFER_DATA, %rcx
 #the size of the buffer
 mov $BUFFER_SIZE, %rdx
 #Size of buffer read is returned in %rax
 int $LINUX_SYSCALL
 
 ###EXIT IF WE’VE REACHED THE END###
 #check for end of file marker
 cmp $END_OF_FILE, %rax
 #if found or on error, go to the end
 jle end_loop

continue_read_loop:
 ###CONVERT THE BLOCK TO UPPER CASE###
 push $BUFFER_DATA #location of buffer
 push %rax #size of the buffer
 call convert_to_upper
 pop %rax #get the size back
 add $4, %rsp #restore %rsp
 
 ###WRITE THE BLOCK OUT TO THE OUTPUT FILE###
 #size of the buffer
 mov %rax, %rdx
 mov $SYS_WRITE, %rax
 #file to use
 mov ST_FD_OUT(%rbp), %rbx
 #location of the buffer
 mov $BUFFER_DATA, %rcx
 int $LINUX_SYSCALL
 
 ###CONTINUE THE LOOP###
 jmp read_loop_begin

end_loop:
 ###CLOSE THE FILES###
 ##NOTE - we don’t need to do error checking on these, because error conditions
 #don’t signify anything special here
 mov $SYS_CLOSE, %rax
 mov ST_FD_OUT(%rbp), %rbx
 int $LINUX_SYSCALL
 mov $SYS_CLOSE, %rax
 mov ST_FD_IN(%rbp), %rbx
 int $LINUX_SYSCALL
 ###EXIT###
 mov $SYS_EXIT, %rax
 mov $0, %rbx
 int $LINUX_SYSCALL
 #PURPOSE: This function actually does the
 # conversion to upper case for a block
 #
 #INPUT:The first parameter is the location

 #of the block of memory to convert
 #The second parameter is the length of
 #that buffer
 #
 #OUTPUT: This function overwrites the current
 #buffer with the upper-casified version.
 #
 ##VARIABLES: %rax - beginning of buffer
 #%rbx - length of buffer
 #%rdi - current buffer offset
 #%cl - current byte being examined
 #(first part of %rcx)
 #


 ###CONSTANTS##
 #The lower boundary of our search
 .equ LOWERCASE_A, 'a'
 #The upper boundary of our search
 .equ LOWERCASE_Z, 'z'
 #Conversion between upper and lower case
 .equ UPPER_CONVERSION, 'A' - 'a'
 
 
 ###STACK STUFF###
 .equ ST_BUFFER_LEN, 8 #Length of buffer
 .equ ST_BUFFER, 12 #actual buffer
 
convert_to_upper:
 push %rbp
 mov %rsp, %rbp
 ###SET UP VARIABLES###
 mov ST_BUFFER(%rbp), %rax
 mov ST_BUFFER_LEN(%rbp), %rbx
 mov $0, %rdi

 #if a buffer with zero length was given
 #to us, just leave
 cmp $0, %rbx
 je end_convert_loop

convert_loop:
 #get the current byte
 movb (%rax,%rdi,1), %cl

 #go to the next byte unless it is between
 #’a’ and ’z’
 cmpb $LOWERCASE_A, %cl
 jl next_byte
 cmpb $LOWERCASE_Z, %cl
 jg next_byte

 #otherwise convert the byte to uppercase
 addb $UPPER_CONVERSION, %cl
 #and store it back
 movb %cl, (%rax,%rdi,1)

next_byte:
 inc %rdi #next byte
 cmp %rdi, %rbx #continue unless
                #we’ve reached the
                #end
                
 jne convert_loop

end_convert_loop:
 #no return value, just leave
 mov %rbp, %rsp
 pop %rbp
 ret

按照书上代码敲的，但是没有结果，也不报错，心累，先这样吧。

2.64位计算机上不同寄存器的作用

不同位数计算机上寄存器(register)：

r8 = AL AH BL BH CL CH DL DH

r16 = AX BX CX DX BP SP SI DI

r32 = EAX EBX ECX EDX EBP ESP ESI EDI

r64 = RAX RBX RCX RDX RBP RSP RSI RDI R8 R9 R10 R11 R12 R13 R14 R15

个人认为，其实作者应该先把各个寄存器的作用列出来，这样读者才能知道代码里为什么使用这个寄存器，不然自己写的时候根本不知道使用哪个寄存器。寄存器的作用可以搜索《System V Application Binary Interface AMD64 Architecture Processor Supplement》手册(如：https://refspecs.linuxbase.org/elf/x86_64-abi-0.99.pdf)，手册里面“Figure 3.4: Register Usage”有介绍。这里把它列出来，方便查看：

Register	Usage	callee saved
%rax	temporary register; with variable arguments passes information<br/>about the number of vector registers used; 1st return register	No
%rbx	callee-saved register	Yes
%rcx	used to pass 4th integer argument to functions	No
%rdx	used to pass 3rd argument to functions; 2nd return register	No
%rsp	stack pointer	Yes
%rbp	callee-saved register; optionally used as frame pointer	Yes
%rsi	used to pass 2nd argument to functions	No
%rdi	used to pass 1st argument to functions	No
%r8	used to pass 5th argument to functions	No
%r9	used to pass 6th argument to functions	No
%r10	temporary register, used for passing a function’s static chain<br/>pointer	No
%r11	temporary register	No
%r12-r14	callee-saved registers	Yes
%r15	callee-saved register; optionally used as GOT base pointer	Yes
%xmm0–%xmm1	used to pass and return floating point arguments	No
%xmm2–%xmm7	used to pass floating point arguments	No
%xmm8–%xmm15	temporary registers	No
%tmm0–%tmm7	temporary registers	No
%mm0–%mm7	temporary registers	No
%k0–%k7	temporary registers	No
%st0,%st1	temporary registers, used to return long double arguments	No
%st2–%st7	temporary registers	No
%fs	thread pointer	Yes
mxcsr	SSE2 control and status word	partial
x87 SW	x87 status word	No
x87 CW	x87 control word	Yes
tilecfig	Tile control register	No

二、英语总结

无。

三、其它

先追求完成，再追求完美，每天看一点。

四、参考资料

1. 编程

(1)Jonathan Bartlett，《Programming From The Ground Up》：https://book.douban.com/subject/1787855/

2. 英语

(1)Etymology Dictionary：https://www.etymonline.com

(2) Cambridge Dictionary：https://dictionary.cambridge.org

欢迎搜索及关注：编程人(a_codists)