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NASM Forum => Using NASM => Topic started by: Banjobeni on November 30, 2010, 09:05:03 PM

Title: Storing addresses of initialized data in other initialized data
Post by: Banjobeni on November 30, 2010, 09:05:03 PM

Hi,

I need to embed some type information in my assembly program for a simple Object-Oriented language. I need to embed a virtual method table and information about the base class of an object.

I tried to embed it in the .data section of my assembly program, for each type in the following format:

address of the base type (or 0 if it does not have a base type)
for every method in that type, an id of the method and the address of the code of this method
0 to indicate end of methods and therefore end of type data

I end up with the following, actual code replaced by nops:

Code: [Select]

section .data
	type_Object dw 0, 0
	type_Object_array dw type_Object, 0
	type_A dw type_Object, 1, method_A_override, 2, method_A_base, 0
	type_A_array dw type_Object, 0
	type_B dw type_A, 1, method_B_override, 3, method_B_sub, 0
	type_B_array dw type_Object, 0
	type_Main dw type_Object, 4, method_Main_main, 0
	type_Main_array dw type_Object, 0

section .text

method_A_override:
	nop
method_A_base:
	nop
method_B_override:
	nop
method_B_sub:
	nop
method_Main_main:
	nop

I compile using -f win32, and I get:

Code: [Select]

VirtualMethod.javali.s:3: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:4: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:4: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:4: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:5: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:6: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:6: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:6: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:7: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:8: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:8: error: COFF format does not support non-32-bit relocations
VirtualMethod.javali.s:9: error: COFF format does not support non-32-bit relocations

I don't understand why these error messages are generated and am thankful for any explanations.

Title: Re: Storing addresses of initialized data in other initialized data
Post by: Frank Kotler on November 30, 2010, 09:41:47 PM

Code: [Select]

	type_Object dw 0, 0
	type_Object_array dw type_Object, 0
        ...

The first line stores two words (16-bit values). This line doesn't cause an error, but may not be what you want. Remaining lines attempt to store the address of "type_Object" in a word - but the address (pointer) is 32 bits, in 32-bit code. Won't fit. Change it to "dd" and it'll work. You may want "dd" throughout...

"dw" looks like it might mean "dword", but it means "data word" - you want "dd", "data dword". An easy mistake to make (ask me how I know). :)

Best,
Frank

Title: Re: Storing addresses of initialized data in other initialized data
Post by: Cyrill Gorcunov on November 30, 2010, 09:44:50 PM

Thanks Frank, indeed. dd should do the trick. we don't support 16bit relocations

Title: Re: Storing addresses of initialized data in other initialized data
Post by: Banjobeni on November 30, 2010, 09:52:27 PM

Thx guys, I interpreted "dw" as doubleword and therefore didn't see the problem. dd worked.