The error you're getting comes out from a very simple fact : the `push` instruction in 32-bit mode accepts 16-bit and 32-bit immediates as arguments. However, the `push` instruction used in 64-bit mode accepts only 16-bit and 64-bit immediates. Since you're clearly compiling your code as 64-bit, the assembler throws an error, since it cannot possibly encode such an instruction. Also, do keep in mind that you force the operand size yourself by adding the `l` suffix to the `push` instruction. Everything I just wrote here is exactly the same for `pop`, except that it accepts registers/memory, not immediates.
However, you also **need** to keep in mind the differences in the ABI between 32-bit and 64-bit Linux systems. The ABI specifies, among other things, how parameters are passed to functions, and how to call the kernel from user-mode applications. Your code is clearly written for 32-bit mode, seeing how it uses the stack for passing arguments and the (very) obsolete `int $0x80` way of invoking syscalls. In order to learn about the 64-bit ABI, see [this document][1].
Alternatively, you have the option of compiling 32-bit code on a 64-bit system. Such an executable will work if you have the necessary 32-bit runtime libraries installed on your 64-bit system. Most distributions allow you to do that in different ways. Your compiler, `as`, has the `--32` switch for emitting 32-bit code.
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