64BIT invoke? problem

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@L.chemist

Joined: 08 Oct 2004
Posts: 14
Location: Russia, Vladimir, Suzdal

@L.chemist 22 May 2007, 09:10

As i understand

Code:

        invoke  Sleep, [P]

should be equivalent to

Code:

        sub     rsp, 0x10
        mov     rcx, [P]
        call    [Sleep]
        add     rsp, 0x10

But "invoke" works if "P" is local variable only.
Otherwise we get error: invalid use of symbol.
What's wrong?

22 May 2007, 09:10

Chewy509

Joined: 19 Jun 2003
Posts: 297
Location: Bris-vegas, Australia

Chewy509 22 May 2007, 23:08

Code:

mov     rcx, [P]

will work fine as long as P is within +-2GB of the function. (Displacements are still limited to 32bit even in Long Mode).

However FASM doesn't know where 'P' will end up if 'P' is a global variable, it needs to use a 64bit space so that the address of 'P' can be inserted by your image loader. But since displacements are limited to 32bits, FASM will generate an error. (Can't load a 64bit value into a 32bit space).

The only way to to load a register with the location of 'P' and pass the register to the function.

eg

Code:

mov rax, P
invoke Sleep, rax

22 May 2007, 23:08

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