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=====Assembling/Compiling "first" code=====
There's been some trouble reported over the assembly and compilation of the first code sample, one that uses the files asm_io.asm, first.asm, and driver.c ... depending on how you go about it, it may work, or not work :) Following are some instructions you can follow so that it will in fact work:
====Obtain Files====
* Copy asm_io.asm, asm_io.inc, first.asm, cdecl.h, and driver.c to someplace in your home directory.
lab46:~/asm$ cp /var/public/asm/bookcode/asm_io.asm .
lab46:~/asm$ cp /var/public/asm/bookcode/asm_io.inc .
lab46:~/asm$ cp /var/public/asm/bookcode/first.asm .
lab46:~/asm$ cp /var/public/asm/bookcode/cdecl.h .
lab46:~/asm$ cp /var/public/asm/bookcode/driver.c .
lab46:~/asm$ ls
asm_io.asm asm_io.inc cdecl.h driver.c first.asm
lab46:~/asm$
asm_io.asm contains the actual assembly code for the various functionality being used in other programs (like first.asm).
asm_io.inc is similar in nature to a header file is in C and C++, identifying important symbols.
first.asm is the actual program.
cdecl.h is a header file which helps to set the appropriate calling conventions to allow interaction between the C and assembly files.
driver.c is a C program that calls the assembly program (not really necessary, but a great example showing you can mix C/C++ and assembly).
====Assemble the assembly files====
* Assemble asm_io.asm and first.asm.
lab46:~/asm$ nasm -f elf -d ELF_TYPE asm_io.asm
lab46:~/asm$ nasm -f elf -d ELF_TYPE first.asm
lab46:~/asm$ ls
asm_io.asm asm_io.inc asm_io.o cdecl.h driver.c first.asm first.o
lab46:~/asm$
Note that when you assemble a file, it creates a .o file, which is the corresponding object code. This is in the native binary code for the machine, but doesn't have the necessary code to actually run. We'd need to link it against the system libraries (using ld, or for the ease of this example, allow gcc to do it while we compile the C portion).
====Compile the C program and link all the object files together====
* We now have just the C file remaining to be processed, so we'll compile it, then link all the files together into an executable in one fell swoop!
lab46:~/asm$ gcc -o first driver.c asm_io.o first.o
lab46:~/asm$ ls
asm_io.asm asm_io.inc asm_io.o cdecl.h driver.c first first.asm first.o
lab46:~/asm$
You can now run "first", which is the executable as formed from the object files of all the assembled and compiled files (gcc sort of abstracts this away from us for the C files, as it does compiling to object and linking in that one step).
=====TODO=====
I announced this in class, but in case anyone missed it or didn't do it at the time.
At your next convenience, I'd like everyone to log into Lab46, and from the base of their home directory, run the following command (example command-line included for emphasis):
lab46:~$ ln -s /usr/local/etc/data/$USER data
This will bring you closer to the grade not-z, and allow you to bask in its infinite love, via your own personalized "data" symlink in your home directory.
Those who have already created their journals will notice the grade not-z has already paid you a visit.
=====RESOURCE LINKS=====
Intel Assembler 80x86 CodeTable http://www.jegerlehner.com/intel/IntelCodeTable.pdf\\
Hello World FAQ (some good notes in here): http://home.comcast.net/~fbkotler/clueless.html\\
Some sample nasm programs (with equivalent C code): http://www.csee.umbc.edu/portal/help/nasm/sample.shtml#Top\\
gdb (some commands and such for nasm): http://www.cs.umbc.edu/portal/help/nasm/nasm.shtml
By far the most useful sources I have found:\\
http://leto.net/writing/nasm.php\\
http://docs.cs.up.ac.za/programming/asm/derick_tut/
DokuWiki Wrap Plugin: http://www.dokuwiki.org/_media/plugin:wrap_plugin_example2.png
One more good resource can be found here: http://www.youtube.com/watch?v=4VNgd3WM95E
The above is a series of 12 or so videos that take you step by step through the basics of NASM (without a C interface!).
nasm x86 Assembly Quick Reference ("Cheat Sheet"): http://www.cs.uaf.edu/2006/fall/cs301/support/x86/
=====EAX register sys call=====
cd: /usr/include/asm-x86_64\\
edit or cat | less to view: unistd.h\\
[[http://bluemaster.iu.hio.no/edu/oca/lin-asm/syscalls.html|Great link for register syscall]]\\
=====Assembly Primes Example=====
http://lab46.corning-cc.edu/user/lleber/start#prime_number_assembly_solution_a
=====Hello World Example=====
1 ; Basic input/output functionality in assembly
2
3 %define SYS_exit 1
4 %define SYS_write 4
5
6 section .text
7
8 global _start
9
10 _start:
11 nop
12
13 write_hello:
14 mov edx, hello_len
15 mov ecx, hello
16
17 .loop:
18 mov eax, SYS_write
19 mov ebx, 1
20 int 80h
21
22 cmp eax, -4096
23 ja error
24
25 add ecx, eax
26 sub edx, eax
27 jnz .loop
28
29 ok:
30 mov eax, SYS_exit
31 xor ebx, ebx
32 int 80h
33 hlt
34
35 error:
36 mov eax, SYS_exit
37 mov ebx, 1
38 int 80h
39 hlt
40
41 section .rodata
42 hello: db "Hello, World!", 10
43 hello_len equ $-hello
=====WTF Does that mean?====
DB means "Define Byte and so it does"
ex.
prompt1 db "Enter a number: ", 0
this defines a variable prompt1 as the string "Enter a number: "
SECTION / SEGMENT is comparable to an "#include" in C or c++. It is used to read a library.
segment .text
EAX, EBX, ECX, ect... all these are registers, think of them as locations... that have commands...
,0 or ,0x..., or,[anything] this is how to end a variable it puts a character at the end, it is all in ascii code, 0x means using hex, so 0x0a would be the new line character. just a 0 would make it octal, so 012 would be new line character.
=====Getting Input from Users=====
mov eax, 3
mov ebx, 1
mov ecx, input ;input is the variable the input is to be stored to
mov edx, 4 ;size of the input in bytes
int 0x80
=====Do Not Argue With my Arguments!=====
The defaults assumed by NASM if you do not specify the qualifiers shown below:
section .text progbits alloc exec nowrite align=16
section .data progbits alloc noexec write align=4
section .bss nobits alloc noexec write align=4
section other progbits alloc noexec nowrite align=1
=====99 Bottles of Beer Example=====
This is an example of an assembly program to do the '99 Bottles of Beer' song.
http://99-bottles-of-beer.net/language-assembler-%28intel-x86%29-1144.html
=====Input Validator [Work In Progress]=====
Not done completely yet, makes use of the SYS_IOCTL invocation
http://lab46.corning-cc.edu/user/lleber/start#input_validator