Login or Register to Ask a Question and Join Our Community

Sponsored Content
Full Discussion: Understanding Assembly Code
Top Forums Programming Understanding Assembly Code Post 302931995 by Azrael on Sunday 18th of January 2015 01:04:54 AM
Old 01-18-2015
Understanding Assembly Code
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!
 

10 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

Understanding Code in IF LOOP

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)
Discussion started by: Ariean
1 Replies

2. UNIX Desktop Questions & Answers

Understanding the code

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)
Discussion started by: Ariean
1 Replies

3. Programming

Need assembly code for C program

Dear Buddies, I need assembly code for a compiled c program in unix. Kindly help me.... Thanking you in advance. (1 Reply)
Discussion started by: karthik537
1 Replies

4. Programming

Help with assembly code

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)
Discussion started by: Learnerabc
2 Replies

5. Shell Programming and Scripting

Help understanding Perl code.

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)
Discussion started by: RedSpyder
0 Replies

6. Shell Programming and Scripting

Help understanding some Perl code.

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)
Discussion started by: RedSpyder
2 Replies

7. Programming

Understanding perl code

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)
Discussion started by: onlinelearner02
0 Replies

8. Shell Programming and Scripting

auto-generating assembly code by variables found by script

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)
Discussion started by: Behrouzx77
1 Replies

9. Shell Programming and Scripting

Help with perl code understanding

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)
Discussion started by: learnbash
1 Replies

10. Shell Programming and Scripting

[Solved] Help understanding this code!!

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)
Discussion started by: Apollo
2 Replies

LEARN ABOUT REDHAT

al

al(1)							      General Commands Manual							     al(1)

NAME

       al, al2 - Mono Assembly Linker

SYNOPSIS

       al [option] [source-files]

DESCRIPTION

       AL is the Mono assembly linkder.

       This linker is used to put together assemblies from a collection of modules (.netmodule files), assembly manifest files and resources.

       Do not confuse this with the monolinker, which is a tool to reduce the size of assemblies based on the code used.

       Use al for processing 1.0 assemblies, use al2 to process 2.0 assemblies.

OPTIONS

       @<filename>
	      Read response file for more options.

       -algid:<id>
	      Algorithm used to hash files. The <id> must be specified in hexadecimal.

       -base:<addr> | -baseaddress:<addr>
	      Base address for the library. THIS FEATURE ISN'T IMPLEMENTED.

       -bugreport:<filename>
	      Create a 'Bug Report' file. THIS FEATURE ISN'T IMPLEMENTED.

       -comp:<text> | -company:<text>
	      This  inserts  the company name into the assembly metadata.  This is equivalent to adding the [AssemblyCompany ("<text>")] attribute
	      into C# source code.

       -config:<text> | -configuration:<text>
	      This inserts the configuration string into  the  assembly  metadata.   This  is  equivalent  to  adding  the  [AssemblyConfiguration
	      ("<text>")] attribute into C# source code.

       -copy:<text> | -copyright:<text>
	      This  inserts  the  copyright  message  into the assembly metadata.  This is equivalent to adding the [AssemblyCopyright ("<text>")]
	      attribute into C# source code.

       -c:<text> | -culture:<text>
	      This inserts the supported culture into the assembly metadata.  This  is	equivalent  to	adding	the  [AssemblyCulture  ("<text>")]
	      attribute into C# source code.

       -delay | -delay+ | -delaysign | -delaysign+
	      The generated assembly will be delay signed.  This is equivalent to adding the [AssemblyDelaySignAttribute (true)] attribute into C#
	      source code.

       -delay- | -delaysign-
	      The generated assembly will be fully signed (i.e. not delay signed).  This is the default option when  signing  (-keyfile  or  -key-
	      name).

       -descr:<text> | -description:<text>
	      This  inserts  a	description  of  the  assembly	into the assembly metadata.  This is equivalent to adding the [AssemblyDescription
	      ("<text>")] attribute into C# source code.

       -e:<filename> | -evidence:<filename>
	      This embed into the assembly the specified file as assembly security evidences.

       -fileversion:<version>
	      Optional Win32 version. This overrides the normal assembly version.

       -flags:<flags>
	      Assembly flags. The <flags> must be specified in hexadecimal.

       -fullpaths
	      Display files using fully-qualified filenames.

       -keyf:<filename> | -keyfile:<filename>
	      Strongname (sign) the output assembly using the key pair present in the specified strong name key file (snk). A  full  key  pair	is
	      required unless the delay signing option is also specified (-delay+).  This is equivalent to adding the [AssemblyKeyFile ("<text>")]
	      attribute into C# source code.

       -keyn:<text> | -keyname:<text>
	      Strongname (sign) the output assembly using the key pair present in the specified container.  Delay  signing  isn't  supported  when
	      using key containers.  This is equivalent to adding the [AssemblyKeyName ("<text>")] attribute into C# source code.

       -main:<method>
	      Specifies the method name of the assembly entry point.

       -nologo
	      Suppress the startup banner and copyright message.

       -out:<filename>
	      Output file name for the assembly manifest.

       -prod:<text> | product:<text>
	      This  inserts  the product name into the assembly metadata.  This is equivalent to adding the [AssemblyProduct ("<text>")] attribute
	      into C# source code.

       -productv[ersion]:<text>
	      This inserts the product version into the assembly  metadata.   This  is	equivalent  to	adding	the  [AssemblyInformationalVersion
	      ("<text>")] attribute into C# source code.

       -t[arget]:<target> | -target=<target>
	      Valid <target>s are: lib | library to create a library (.dll), exe to create a console executable (.exe), and win | winexe to create
	      a Windows executable (.exe).

       -template:<filename>
	      Specifies an assembly to get default options from.

       -title:<text>
	      This inserts an assembly title into the assembly metadata.  This is equivalent to adding the  [AssemblyTitle  ("<text>")]  attribute
	      into C# source code.

       -trade:<text> | -trademark:<text>
	      This  inserts  a	trademark  message  into  the  assembly metadata.  This is equivalent to adding the [AssemblyTrademark ("<text>")]
	      attribute into C# source code.

       -v:<version> | -version:<version>
	      This inserts the assembly version into the assembly metadata. You can use * to auto-generate remaining numbers.  This is	equivalent
	      to adding the [AssemblyVersion ("<text>")] attribute into C# source code.

       -win32icon:<filename>
	      Use this icon for the output.

       -win32res:<filename>
	      Specifies the Win32 resource file.

       -? | -help
	      Display information about AL

SEE ALSO

       sn(1), monolinker(1)

COPYRIGHT

       Copyright (C) 2005 Novell, Inc (http://www.novell.com)

MAILING LISTS

       Visit http://lists.ximian.com/mailman/listinfo/mono-devel-list for details.

WEB SITE

       Visit: http://www.mono-project.com for details

																	     al(1)
All times are GMT -4. The time now is 11:03 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy