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> Macroinstructions > Conditional definition based on type? |
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revolution 29 Oct 2009, 02:16
Code: macro push [args] { common local done done equ 0 match =esi=+=1,args \{ inc esi push esi dec esi done equ 1 \} match =0,done \{ push args \} } esi_plus_one equ esi+1 mov eax, [esi_plus_one] push esi_plus_one |
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29 Oct 2009, 02:16 |
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a rabbit 29 Oct 2009, 02:38
Thanks for the replay!
It won't work for the following situation, though: Code: mov eax, esi_plus_one Also I'd like it to support all the instructions. Is there any way to make a global macro or something like that? |
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29 Oct 2009, 02:38 |
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revolution 29 Oct 2009, 02:51
fasm does not support inline macros. Perhaps with fasm2 you may be able to do it.
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29 Oct 2009, 02:51 |
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a rabbit 29 Oct 2009, 03:13
Actually, what I'm trying to do is to write some position-independent code, which I'm going to inject to another process.
It's really easy to do on x64, as the addresses are relative to RIP by default, but a bit troublesome on 32-bit assembly. Here's my code: (position-dependent) Code: format PE GUI 4.0 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Code LoadDll: .LoadLibrary: dd 0xdeadbeef ; kinda variable 1 .GetProcAddress: dd 0xdeadbeef ; kinda variable 2 ; LoadLibrary(dll_str); push dll_str call dword [.LoadLibrary] ; *.LoadLibrary = eax; mov dword [.LoadLibrary], eax ; GetProcAddress(eax, import_name); push import_name push eax call dword [.GetProcAddress] ; *.GetProcAddress = eax; mov dword [.GetProcAddress], eax ; return; retn 4 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Data import_name db 'SetOptions',0 dll_str db 'C:\test.dll',0 And here is my solution to make the code position-independent: Code: format PE GUI 4.0 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Macros for position-independency macro _set_as_index reg ; will be set to .pstart and used, don't modify! { index_reg equ reg call $+5 pop index_reg delta = ($-1)-.pstart } macro _set_other_as_index reg { mov reg, index_reg restore index_reg index_reg equ reg } macro _label_cmd label, [cmd] { common _the_label equ index_reg if (label-.pstart)-delta <> 0 add index_reg, (label-.pstart)-delta end if cmd restore _the_label delta = (label-.pstart) } macro _laptr_cmd label, [cmd] { common _the_label equ index_reg+(label-.pstart)-delta cmd restore _the_label } ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Code LoadDll: .pstart: .LoadLibrary: dd 0xdeadbeef .GetProcAddress: dd 0xdeadbeef ; we use edi as our index! push edi _set_as_index edi ; LoadLibrary(dll_str); _label_cmd dll_str, push _the_label _laptr_cmd .LoadLibrary, call dword [_the_label] ; *.LoadLibrary = eax; _laptr_cmd .LoadLibrary, mov dword [_the_label], eax ; GetProcAddress(eax, import_name); _label_cmd import_name, push _the_label push eax _laptr_cmd .GetProcAddress, call dword [_the_label] ; *.GetProcAddress = eax; _laptr_cmd .GetProcAddress, mov dword [_the_label], eax ; return; pop edi retn 4 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Data import_name db 'SetOptions',0 dll_str db 'C:\test.dll',0 It works, and the produced binary isn't too junky, but the source is 
Maybe you have some suggestions for a better solution? P.S. revolution wrote: fasm does not support inline macros. Any assembler does? |
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29 Oct 2009, 03:13 |
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Fanael 29 Oct 2009, 07:08
Microsoft Macro Assembler does.
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29 Oct 2009, 07:08 |
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a rabbit 29 Oct 2009, 22:35
Thanks.
push esi+1 assembles as PUSH ESI/PUSH 1 Is that a feature? O_o push 1+1 assembles correctly. |
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29 Oct 2009, 22:35 |
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revolution 30 Oct 2009, 02:11
The expression parser is greedy. That mean that if it can evaluate an expression it will. So 1+1 evaluates to 2 and pushes 2. With esi+1 the evaluator can only parse esi and then the next try finds +1. 'push 1 2 3 4 +5 -6 +7' will push: 1, 2, 3, and then 2.
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30 Oct 2009, 02:11 |
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