As the title suggests, I want to better understand the following assembly code:
Code:
section .text
global main ; must be declared for linker (gcc)
main: ; tell linker entry point
mov edx, len ; message length
mov ecx, msg ; message to write
mov ebx, 1 ; file descriptor (stdout)
mov eax, 4 ; syscall for write (sys_write)
int 0x80 ; call kernel
mov edx, 9 ; message length
mov ecx, s2 ; message to write
mov ebx, 1 ; file descriptor (stdout)
mov eax, 4 ; syscall number for write (sys_write)
int 0x80 ; call kernel
mov eax, 1 ; system call (sys_exit)
int 0x80 ; call kernel
section .data
msg db 'Displaying 9 stars', 0xa ; a message
len equ $ - msg ; length of message
s2 times 9 db '*'
As you can see I already have descriptions in the comments from the tutorial I found here. Here are some of the things I don't understand:
1. - What is s2? Is this just a variable or a register I know nothing about?
2. When '1' is moved into ebx, is this a parameter to the sys_exit later called in eax? I found a listing of Linux syscalls here and it does seem sys_exit does take one parameter in ebx that's an integer. If this is the case why not exit cleanly with zero?
I just want to make sure I understand everything correctly in this. Thanks in advance!
My last assembler is quite some days ago, but I'd say
1) s2 is (the address of) a constant ("*********") defined in the last line of your listing
2) eax holds the call No. (function selector) for the linux kernel interrupt 0x80 see here. As the return value in ebx is not explicitly set, it seems to rely on the value returned by sys_write to be used as the exit code.
That actually makes a lot of sense. I think I had just been looking at it too long and over analyzing things. The link you provided seems to be the same as the pdf I'm reading, but with some extra information. Thanks for the clarity!
Hi guys,
I am still learning awk and much apprecated to shed some light on the following: the questions asked is below!
{
total = i = 0
do {
++i
total += $i
} while ( total <= 100 )
print i, ":", total
}
File used:
cat test.do
45 25 60 20
10 105 50 40
33 5 9 67
108 3 5 4 (2 Replies)
Hi,
I need to understand below perl code, can some one advise me.
perl -MDate::Parse -e'BEGIN{$main::now=time;$main::old=(time-60*30)}' -nE'if(/^(\w+\s+\d+\s+\d+:\d+:\d+)/) {$t=str2time $1; $t > $old && $t < $now && print}' (1 Reply)
Hi everybody
I'm working on a list of registers(flip-flops to be exact), now i need to extract some value from this list and use them as arguments to pass them to some assembly code
for example i have:
118 chain79 MASTER (FF-LE) FFFF 1975829 /TCK F FD1TQHVTT1 ... (1 Reply)
What is the difference between the two statements below?
A:
$a->{"$fruit"}->{"$color"}->{size} = $size
B:
$size = $a->{"$fruit"}->{"$color"}->{size}
Please assist. Thanks! (0 Replies)
Well, I found myself trying to fix some Perl code (Ive never done any Perl in my life) and I pinpointed the place where the bug could be. But to be sure I have to know what does a few line of code mean:
$files_lim =~ (/^\d*$/)
$files_lim =~ (/^\d*h$/)
$files_age =~ s/h//
The code where... (2 Replies)
Well, I found myself trying to fix some Perl code (Ive never done any Perl in my life) and I pinpointed the place where the bug could be. But to be sure I have to know what does a few line of code mean:
$files_lim =~ (/^\d*$/)
$files_lim =~ (/^\d*h$/)$files_age =~ s/h//The code where this was... (0 Replies)
I want make simple assembly code for some thing like this a^6+6a^2+2a and range of a is between -3 to 3. I tried but it is not working properly. As this is my first assembly program that I am going to try, I want some help with it.
I found this example online but i dont want this kind of... (2 Replies)
hello all,
May i know what is this "DEBUG_ME $DEBUG_CMD main" doing in the below code. I am confused with alias also "alias DEBUG_ME='#'". Thanks for your help.
set -x
alias DEBUG_ME='#'
if ; then
. /product/apps/informatica/v7/pc/ExtProc/debug.ksh "$1"
fi
# Declaring the... (1 Reply)
Hello All,
I would like to know and understand the difference between the below 3 IF loops and also if possible what are the different other parameters i could use other than those mentioed in the below lF LOOP conditions, appreciate your help.
Thanks,
Sam. (1 Reply)
