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assemblyx86gnu-assembler

Difference between two different variable declarations in asm

What's the difference between the following gas assembly?

x: .long 500

And:

x = 500

Can both be used interchangeably or, if not, why is one preferred over the other?

Solution

  • They’re not interchangeable. The first one:

        x:    .long 500

    creates a 4-byte space in memory initialized with the given value. The label x represents the address of that memory location.

    The second one:

        x = 500

    doesn’t create any memory. It sets the symbol x to the value 500, not to an address.