Btukfyl

Here is my question:

I wrote a piece of code of assemble. It could read a file, transform the content to the uppercase and print the outputs in a newfile.

I complie and link the assemble code with:

as -gstabs read-files.s -o read-files.o

ld read-files.o -o read-files

And a test like "./read-files input-file output-file" works well.

But what if I want to debug this piece of code with gdb? I tried, but:

when I set the breakpoint and args of target code in gdb with:

(gdb) b *_start+1

(gdb) run test-file TEST-FILE

It will end with a segmentfault immediately.

Can I really debug this code like what I just stated aboved? Thanks

And the assemble code is here:

 .section .data

 .equ SYS_OPEN, 5

 .equ SYS_WRITE, 4

 .equ SYS_READ, 3

 .equ SYS_CLOSE, 6

 .equ SYS_EXIT, 1

 .equ O_RDONLY, 0

 .equ O_CREAT_WRONLY_TRUNC, 03101

 .equ STDIN, 0

 .equ STDOUT, 1

 .equ STDERR, 2

 .equ LINUX_SYSCALL, 0x80

 .equ END_OF_FILE, 0

 .equ NUMBER_ARGUMENTS, 2



 .section .bss

 .equ BUFFER_SIZE, 500

 .lcomm BUFFER_DATA, BUFFER_SIZE



 .section .text

 .equ ST_SIZE_RESERVE, 8

 .equ ST_FD_IN, -4

 .equ ST_FD_OUT, -8

 .equ ST_ARGC, 0

 .equ ST_ARGV_0, 4

 .equ ST_ARGV_1, 8

 .equ ST_ARGV_2, 12



 .globl _start

_start:

 movl %esp, %ebp

 subl $ST_SIZE_RESERVE, %esp



open_files:

open_fd_in:

 movl $SYS_OPEN, %eax

 movl ST_ARGV_1(%ebp), %ebx

 movl $O_RDONLY, %ecx

 movl $0666, %edx

 int $LINUX_SYSCALL



store_fd_in:

 movl %eax, ST_FD_IN(%ebp)



open_fd_out:

 movl $SYS_OPEN, %eax

 movl ST_ARGV_2(%ebp), %ebx

 movl $O_CREAT_WRONLY_TRUNC, %ecx

 movl $0666, %edx

 int $LINUX_SYSCALL



store_fd_out:

 movl %eax, ST_FD_OUT(%ebp)



read_loop_begin:

 movl $SYS_READ, %eax

 movl ST_FD_IN(%ebp), %ebx

 movl $BUFFER_DATA, %ecx

 movl $BUFFER_SIZE, %edx

 int $LINUX_SYSCALL



 cmpl $END_OF_FILE, %eax

 jle end_loop



continue_read_loop:

 pushl $BUFFER_DATA

 pushl %eax

 call convert_to_upper

 popl %eax

 addl $4, %esp



 movl %eax, %edx

 movl $SYS_WRITE, %eax

 movl ST_FD_OUT(%ebp), %ebx

 movl $BUFFER_DATA, %ecx

 int $LINUX_SYSCALL



 jmp read_loop_begin



end_loop:

 movl $SYS_CLOSE, %eax

 movl ST_FD_OUT(%ebp), %ebx

 int $LINUX_SYSCALL



 movl $SYS_CLOSE, %eax

 movl ST_FD_IN(%ebp), %ebx

 int $LINUX_SYSCALL



 movl $SYS_EXIT, %eax

 movl $0, %ebx

 int $LINUX_SYSCALL



 .equ LOWERCASE_A, 'a'

 .equ LOWERCASE_Z, 'z'

 .equ UPPER_CONVERSION, 'A' - 'a'

 .equ ST_BUFFER_LEN, 8

 .equ ST_BUFFER, 12



convert_to_upper:

 pushl %ebp

 movl %esp, %ebp



 movl ST_BUFFER(%ebp), %eax

 movl ST_BUFFER_LEN(%ebp), %ebx

 movl $0, %edi



 cmpl $0, %ebx

 je end_convert_loop



convert_loop:

 movb (%eax, %edi, 1), %cl

 cmpb $LOWERCASE_A, %cl

 jl next_byte

 cmpb $LOWERCASE_Z, %cl

 jg next_byte



 addb $UPPER_CONVERSION, %cl

 movb %cl, (%eax, %edi, 1)



next_byte:

 incl %edi

 cmpl %edi, %ebx

 jne convert_loop



end_convert_loop:

 movl %ebp, %esp

 popl %ebp

 ret