assmbly. Oh my goodness

alaios · 11-14-2003, 01:37 AM

Hi there iam trying to start reading linux assembly but i am really confused. I am trying to see what i must follow, something like a standars.
For example so many programs nasm,yasm,*asm,*asm* with different syntax and different operations. I want to know what is the most popular of them and where i must turn my attention

moved to the Programming forum

worldmagic · 11-14-2003, 06:20 AM

The most used one has to be the "as" program. The GNU Compiler translates C into Asm and then hand it over to "as" to create the objectfiles that later can be linked with "ld". If you want to look at the syntax, the easyest way is actualy to compile a very simple C program, but tell the compiler to output the assembler data as files instead of objectfiles.

This command:
gcc -S mytest.c

Will result in the files mytest.s (This is the assembly file)

Happy Hacking =)

kev82 · 11-14-2003, 10:36 AM

by worldmagic
The most used one has to be the "as" program

is it? i thought it wasnt designed for human use and is a real pain in the ass to use? but i might be wrong. if you like intel syntax then i would reccomend nasm, if you prefer AT&T syntax then the only assembler i know of is as but im sure there are more, check out the linux assembly howto hosted on tldp.org somewhere.

alaios · 11-14-2003, 11:26 AM

I have just read it but still i can not define the most usable assembler

LogicG8 · 11-14-2003, 01:25 PM

Definately go with nasm.
gas (gnu as) might be the most used,
but it's only b/c gcc uses it behind the
scenes. at&t syntax is a real pain.

Plus as a bonus if you ever need to code
a win32 platform you won't have to
struggle to remember which way operands
work.

Intel
mov dest, src

gas
mov src, dest

Most asm tutorials on the web use
intel and only a handful discuss
gas. Your life will be easier if you
use nasm.

LogicG8 · 11-14-2003, 01:29 PM

Oh yeah, just remembered, while one of the biggest reasons
to learn at&t syntax has been that gcc can output the compilation
of C program in it so you can study the code it generates. Since
version 3.0 GCC also puts out assembly language in intel format
with the -mintel-syntax switch...

alaios · 11-14-2003, 02:34 PM

what is at&t syntax?

infamous41md · 11-14-2003, 02:57 PM

att syntax is a pain? lmao, what makes more sense?

move eax into edx:

a) movl %eax, %edx ---ATT
b) mov %edx, [dword ptr] %eax ---intel

?
reading right to left and using a single letter prefix for operand size? or reading backwards and using a "cast" for operand size?

kev82 · 11-14-2003, 05:07 PM

depends what your used to i suppose

with intel you dont need the cast unless storing/load from memory location, AT&T has a cast with each instruction as it must be postfixed with with either b, w, or l also AT&T has $ and % everywhere wheras intel doesnt which makes it easier to read, as for src, dest or dest, src i think that should be left to usenet wars.

infamous41md · 11-15-2003, 02:06 PM

i agree it is somewhat of a religious war, but COME ON we read from left to right!

ok im just causing trouble i'll shut up

alaios · 11-15-2003, 02:44 PM

A conclusion? What to decide? Do u know any visual debugger like code view . I want to view the values of the registers.....
Info about debuggers?
Thx guys

infamous41md · 11-15-2003, 05:03 PM

view the registers? gdb <exe>; set a breakpoint somewhere 'br <function/memaddr>'; run the program 'r'; view the regs 'info registers'

alaios · 11-16-2003, 01:36 AM

Something more visual?

/bin/bash · 11-16-2003, 04:12 AM

http://webster.cs.ucr.edu/