In article <1150289464.309495.102720@f6g2000cwb.googlegroups.c om>,
"Chinlu" wrote:

> Hello,
>
> I'm a newbie programming in assembler, and I'm trying to implement a
> tiny-wget function in a program I'm doing.
>
> I'm also new to network programming, my target os is linux. One of the
> problems I'm facing is `connect'. it doesn't exist as such in assembler
> as it does in c. Though I've had hard times with google lookin for some
> sort of explanation to this regard, I haven't found anything that makes
> me understand.

How do you invoke other system calls that take structures as parameters,
like stat()? There's nothing different about connect() in this regard.
You need to determine the mapping from C structures to raw memory
layout, and then fill in a block of memory appropriately in your
program. You can do this by writing a C program that calls connect()
and then looking at the generated assembler from your compiler.

>
> Currently all that I'm able to do is this:
>
> http://es.geocities.com/ucho_trabajo/asm/tcp.s.txt
>
> Which is nothing but a call to `socket', aquiring a socket descriptor.
> For ease I'm curently trying to connect to my sendmail daemon, since
> being able to retrieve something from it, might mean that I would as
> well with a ftp or http addres.

Huh? You don't retrieve things from sendmail, it's used to send mail
out.

>
> Althought I've got nice examples like this:
>
> http://asm.sourceforge.net/articles/...rc.html#socket
>
> I just cannot figure out how a call that tries to connect to a website
> or ftp, trying to retrieve data could be done.
>
> I know I can link to libc and use `connect' but it's not what I'm
> trying to. So I'm wondering if any expert could roughly describe the
> process at such level for me, so I can implement it.

I'm not sure what else you expect to do. Connect() is the only
documented API for this. Internally it may perform other operations,
but that's system-dependent.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

Hello,

> How do you invoke other system calls that take structures as parameters,
> like stat()? There's nothing different about connect() in this regard.
> You need to determine the mapping from C structures to raw memory
> layout, and then fill in a block of memory appropriately in your
> program. You can do this by writing a C program that calls connect()
> and then looking at the generated assembler from your compiler.

I use to, but either, the output it's so verbose that I get lost in it,
or I'm not able to understand it. Too less experienced I'd say.

My confusion was more due to the overall structure and workflow, as I
was missing linux/net.h, where sys_connect is defined. I started
understanding when I saw it that there's an atomic system call which is
`socketcall', that gets driven by this definitions.

> Huh? You don't retrieve things from sendmail, it's used to send mail
> out.

I was refering to the greeting message or however it is called, as you
can see if you telnet almost any server. I achieved this yesterday, you
can see the first results in here:

http://es.geocities.com/ucho_trabajo/asm/connect2.s.txt
http://es.geocities.com/ucho_trabajo...ct2.strace.txt
http://es.geocities.com/ucho_trabajo...nnect2.out.txt

> I'm not sure what else you expect to do. Connect() is the only
> documented API for this. Internally it may perform other operations,
> but that's system-dependent.

Yes, and that leads me to another question. Yesterday, someone was kind
enough to post a daytime client program written in assembler, for
`gas'. And I could see how endianness was more or less handled.

Trying to get the best out of my flu, I started porting my app. to a
`.S' extension and compiling it through `gcc' instead of `as', so I can
get advantage on `gcc' and cpp's macro-proccesing capabilities, which
makes `gas' more flexible and powerfull, I might add.

I was also reading the autobook and autoconf/automake info pages, so I
could start looking at portability issues from other perspective, and
making this code more or less shareable from the begining. I'm using a
config header and included:

#if HAVE_CONFIG_H
# include
#endif

At the top of my assembler file. My question is, I guess I should get
to know target host's endiannes via some sort of m4 or autoconf macro,
and then write a:

#def big_endian
or
#def little_endian

in my `config.h'. Then, throughout all of my program I should split
code depending on endiannes, like this:

#ifdef big_endian
... big endian code ...
#else
... litle endian code ....
#endif

Shouldn't I? Also, could you please tell me other things I might be
aware of if trying to make this code shareable?

I haven't got a clue on how other systems handle tcp/ip, so by now it's
only for linuxes, but are there other potential portability issues that
would stop me from sharing this code with other linuxes?

Kind Regards,

In article <1150374780.733101.202510@y41g2000cwy.googlegroups. com>,
"Chinlu" wrote:

> I haven't got a clue on how other systems handle tcp/ip, so by now it's
> only for linuxes, but are there other potential portability issues that
> would stop me from sharing this code with other linuxes?

99.9% of programmers these days use a high-level language like C, not
assembler. In C the common way to handle endianness is with macros like
htons() and presentation libraries like XDR. I don't know if there's a
repository of similar techniques for assembly programming -- if there's
an assembly newsgroup, that would probably be the best place to start.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***