I'm currently writing a token interpreter using Fasm 1.49, and I'm having some trouble encoding execution tokens based on a declared label, which is the address of the routine who's token I wish to encode.

The token is a 32-bit code, where the top 2 bits have special functions and are shifted out of the token by the inner interpreter, and the remaining bits (after the two shifts) is the address to a dword-align function.

So, a token is created by something like:

dd (FunctionLabel shr 2) + bits

BUT, when I include something like this in the source:

dd (Bye shr 2) + $80000000 ; execute Bye

fasm returns the following message:

"Error: Invalid Expression".

and highlights the line.

What am I doing wrong? I've tried many different ways, up to defining a macro to do the calculations.

Any help will be much appreciated.

-gustavo

Such thing happens when you use output format that uses the relocatable labels, like PE. If you are using PE and don't plan to include the relocations in your program, you can use the solution that was provided here: http://board.flatassembler.net/topic.php?t=37#395.

I have this problem with an ELF file that I don't need to be relocated. However, format ELF at 0x00100000 gives me "extra characters on line". What can I do?

If possible use "format elf executable" instead. I think there is no solution for object ELF since fasm always construct them relocatable.

Well, there is one, but no idea if you can trust the calculated address on run-time

good catch! "load" shouldn't be allowed from relocated data. But i am not sure if this is possible in current FASM

> If possible use "format elf executable" instead.
Then sections doesn't seem to work. But never mind, I just fill in the data at run time.

Plue, but you can use segments instead, no?

vid, that trick is ancient, I even robbed it from cris' assembly listing generator. I think it would be very painfull for fasm to keep tracking of memory content to check when load can be allowed so this "backdoor" will hardly dissapear.

And looking at the FAQ I see another much simpler method (but disables relocations completely)

But how do you ensure that section 'text' will be loaded at $8040000 is the question...

at runtime, "call / pop eax" and check address, no?

But then, for what was useful to precalc the XOR operation if then it must be corrected by a delta?

You can also check and exit if the address is not the desired one but that is not a very descent program and would be better to calculate operations with labels at run-time instead.

not corrected.


that is what i meant. and of course, it is a stupid idea