[Solved] Assembly - Passing Integer Command Line Parameters

Question

This is as good a place to ask as any I suppose, so here goes.
I'm really only interested in knowing if it is at all possible to push actual values, in this case integers, on the stack from the command Line, i.e. passing arguments and if so how, because as far as I can gather, it is simply impossible to pass anything other than strings.
Yes I am a noob at assembly, if anyone should doubt that.
Best regards.
I thought the best thing to do is simply to explain what I'm actually doing.
In short, I need to derive the Lightness/Luminance level of a pixel. This of course can be done a number of way. Initially I experimented with image magic, but when I couldn't figure it out, I thought: "Hey, why not learn something along the way?"
So here I an, trying to do some assembly under linux.
For those interested the process is actually rather sinbple:
1. get and convert the rgb input as needed.
2. Determine the highest and lowest channel (progress so far):
mov ax, $1;
mov cx, $2;
mov dx, $3;
cmp ax, cx;
jng else;
mov ax, ax;
mox bx, cx;
jmp next;
else:
mov ax, cx;
mov bx, ax;
next:
cmp dx, ax;
jng else2;
mov ax, dx;
jmp end;
else2:
cmp bx, dx;
jnl end;
mov bx, dx
end:
3. add the two values and divide by two. possible implement a way to check if the addition is even or not, so to enable proper rounding.
4. output the result in one form or another.
Last edited by zacariaz (2012-09-03 20:30:14)

Answer 1

Lux Perpetua wrote:
zacariaz wrote:
Well, at the same time it makes sense and it don't.
I makes sense to have a "common language", so to speak, so that various applications can be piped together.
At the same time however, it's a waste to have the majority of the code dedicated to making conversions. First one for the input and then one for the output.
But that life I guess.
Thanks for now.
When you run a program on a Linux system, it ultimately all boils down to the following function:
int execve(const char *path, char *const argv[], char *const envp[]);
Without going into full detail: the first argument is the path to the program being executed. The second argument is literally the "argv" argument list the program sees (which is a null-pointer-terminated array of pointers to null-character-terminated strings). The third argument is the environment. Relevant to you is the second argument. It doesn't matter if it's an assembly program, a C program, or a shell script; the "command-line" arguments to the program, i.e., the argv array, are pointers to strings.
Lest you have the brilliant idea to take an integer apart into bytes and stick them in a string as one of the argument as some others have suggested, you should consider the following: what if one of the bytes of the integer is 0? That technically ends the "string," and everything following that byte is discarded by execve. Adding 1 to all the bytes wouldn't work, since 0xff would wrap around to 0 again. To make it work, you'd need to encode the integer in some other complicated way to avoid null characters and then decode it inside your program. In other words, you might as well just pass an ordinary string and parse it with atoi or strtol.
You are of course right, and thanks for the very nice explanation, however it's still a pain in the but.
I like working with number, not with letters, but enough of this.
Thanks to all and to all a good night, day or whatever you please.
Best regards