我正在解决this这本书中的练习部分。
我的问题是关于本书中的toupper示例。
问题：
重写程序，以便它使用.bss节中的存储空间，而不是 而不是用于存储文件描述符的堆栈。
可以在website上找到默认代码。
我的代码：
#Rewrite the program so that it uses storage in the .bss section rather than the
#stack to store the file descriptors.
#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 through 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/include/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 16,000 for various
# reasons.
.equ BUFFER_SIZE, 500
.lcomm BUFFER_DATA, BUFFER_SIZE
.equ ST_FD_IN, 10
.equ ST_FD_OUT, 10
.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
movl %esp, %ebp
#Allocate space for our file descriptors
#on the stack
subl $ST_SIZE_RESERVE, %esp
open_files:
open_fd_in:
###OPEN INPUT FILE###
#open syscall
movl $SYS_OPEN, %eax
#input filename into %ebx
movl ST_ARGV_1(%ebp), %ebx
#read-only flag
movl $O_RDONLY, %ecx
#this doesn't really matter for reading
movl $0666, %edx
#call Linux
int $LINUX_SYSCALL
store_fd_in:
#save the given file descriptor
movl %eax, ST_FD_IN(%ebp)
open_fd_out:
###OPEN OUTPUT FILE###
#open the file
movl $SYS_OPEN, %eax
#output filename into %ebx
movl ST_ARGV_2(%ebp), %ebx
#flags for writing to the file
movl $O_CREAT_WRONLY_TRUNC, %ecx
#permission set for new file (if it's created)
movl $0666, %edx
#call Linux
int $LINUX_SYSCALL
store_fd_out:
#store the file descriptor here
movl %eax, ST_FD_OUT
###BEGIN MAIN LOOP###
read_loop_begin:
###READ IN A BLOCK FROM THE INPUT FILE###
movl $SYS_READ, %eax
#get the input file descriptor
movl ST_FD_IN, %ebx
#the location to read into
movl $BUFFER_DATA, %ecx
#the size of the buffer
movl $BUFFER_SIZE, %edx
#Size of buffer read is returned in %eax
int $LINUX_SYSCALL
###EXIT IF WE'VE REACHED THE END###
#check for end of file marker
cmpl $END_OF_FILE, %eax
#if found or on error, go to the end
jle end_loop
continue_read_loop:
###CONVERT THE BLOCK TO UPPER CASE###
pushl $BUFFER_DATA #location of buffer
pushl %eax #size of the buffer
call convert_to_upper
popl %eax #get the size back
addl $4, %esp #restore %esp
###WRITE THE BLOCK OUT TO THE OUTPUT FILE###
#size of the buffer
movl %eax, %edx
movl $SYS_WRITE, %eax
#file to use
movl ST_FD_OUT, %ebx
#location of the buffer
movl $BUFFER_DATA, %ecx
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
movl $SYS_CLOSE, %eax
movl ST_FD_OUT, %ebx
int $LINUX_SYSCALL
movl $SYS_CLOSE, %eax
movl ST_FD_IN, %ebx
int $LINUX_SYSCALL
###EXIT###
movl $SYS_EXIT, %eax
movl $0, %ebx
int $LINUX_SYSCALL
###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:
pushl %ebp
movl %esp, %ebp
###SET UP VARIABLES###
movl ST_BUFFER(%ebp), %eax
movl ST_BUFFER_LEN(%ebp), %ebx
movl $0, %edi
#if a buffer with zero length was given
#to us, just leave
cmpl $0, %ebx
je end_convert_loop
convert_loop:
#get the current byte
movb (%eax,%edi, 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, (%eax,%edi,1)
next_byte:
incl %edi #next byte
cmpl %edi, %ebx #continue unless
#we've reached the
#end
jne convert_loop
end_convert_loop:
#no return value, just leave
movl %ebp, %esp
popl %ebp
ret
我尝试在.bss节中定义（.equ）文件描述符（即，将它们保留10个空格），然后在代码中使用它们。但是，尽管尝试了不同的方法，但我还是无法使它起作用。
能帮我吗？谢谢你。
答案 0 :(得分：1)
.equ不保留空间。而是为标签分配一个值。要保留空间，请使用.space或.lcomm指令。