Far Calls in 64-bit

[ironman]

Hello all.

I was looking at the test files, in particular far64.asm. I was experimenting with the following line:

Code: [Select]

call qword far [rax]
In particular, I tried replacing rax with an immediate:

Code: [Select]

call qword far [0x7ffff7c11ca0]
Oddly, this gives me an error:

far64.asm:5: warning: dword data exceeds bounds

But I am not using a dword. Also, I've checked to see if the warning has any bearing on the output. Indeed it does, the bytes output are incorrect. Thanks for any help.

[Rob Neff]

That is a known bug that we hope will be fixed by the next release.

[Cyrill Gorcunov]

Yeah, just ignore such warnings for a while.

[Frank Kotler]

Yeah, the warning is known, and should be ignored, but he says the bytes are wrong. Looks like signed 32-bit... which I think is correct... but I don't know enough 64-bit to be sure.

BTW, "call strict qword" doesn't "fix" it...

Thanks for the feedback, Matt.

Best,
Frank

[ironman]

I am finding that this problem extends to not just CALL instructions, but several others as well. For example, even

Code: [Select]

mov rbx,[0xaaaaaaaaaaaaaaaa]

creates incorrect bytes. This example is pulled directly from test/riprep.pl. These problems are all subverted by just moving the value of interest into a 64-bit register and then using as needed, but it is awkward to do it this way.

-Matt

[Cyrill Gorcunov]

In 64 bit mode the EA displacements are 4 bytes long (the parasite warning we have sometime due to sign extension is a different problem).

[Cyrill Gorcunov]

Ah, guys, you might be meaning moffsets (ie direct memory-offset MOVs)? If so such MOV requires qword inside square brackets.

For example

Code: [Select]

[bits 64]
mov rax, [qword 0x1111111111111111]
mov al,  [qword 0x1111111111111111]
mov eax, [qword 0x1111111111111111]


[Cyrill Gorcunov]

Ah, guys, you might be meaning moffsets (ie direct memory-offset MOVs)? If so such MOV requires qword inside square brackets.

For example

Code: [Select]

[bits 64]
mov rax, [qword 0x1111111111111111]
mov al,  [qword 0x1111111111111111]
mov eax, [qword 0x1111111111111111]


And it operates with r/e/ax register only.

[Cyrill Gorcunov]

Please check out "11.2 Immediates and Displacements in 64-bit Mode" of nasm manual.
http://www.nasm.us/xdoc/2.09.10/html/nasmdo11.html#section-11.2