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redsock



Joined: 09 Oct 2009
Posts: 435
Location: Australia
redsock 05 Sep 2014, 03:42
Hey all, hoping for some assistance with my 32 bit string macro. It works well enough the way I have it, but surely there is a much, much better way to do it that I just haven't been able to work out.

Basically, there are two problems with it: 1) I couldn't figure out a better (or the proper) way to do it without wasting space in my end-resultant binary for my "scratch space" to promote normal strings to 32 bits. 2) I tried several things to get my macro to do comma-delimited lists, such as 'hello world',10,'hello again',10 but finally decided it is better to just ask you guys Smile hopefully y'all can enlighten me, hahah.

Code:
static_string_limit = 256

static_string_space:
        db static_string_limit dup 0

macro cleartext name*,val* {
        local AA,BB,.WTF,CC,DD,I,Si,J
        align 16
        name:
        dq      AA
        .WTF:
        db      val
        BB = ($ - .WTF)
        AA = BB
        if AA > static_string_limit
                display `name # " name is too long (static_string_limit setting)",13,10
                err
        end if
        ; so now, we have declared a straight byte version
        CC = AA shl 2
        ; CC now has how many bytes we really need for it
        DD = CC - BB
        ; so we can declare our extra space here:
        db      DD dup 0
        ; now we need to COPY the BB# of bytes stored at .WTF into the static_string_space (temporarily)
        ; and once it is there, we can them promote it to 32 bits back into the address at WTF
        ; and then clear the bytes we wrote into at static_string_space so they don't get dumped into
        ; our binary
        ; TODO: there has to be a way to do this without using the static_string_space
        I = 0
        repeat BB
                load Si byte from .WTF+I
                store byte Si at static_string_space+I
                I = I + 1
        end repeat
        I = 0
        J = 0
        repeat BB
                load Si byte from static_string_space+I
                store dword Si at .WTF+J
                I = I + 1
                J = J + 4
        end repeat
        I = 0
        J = 0
        repeat BB
                store byte J at static_string_space+I
                I = I + 1
        end repeat
}
    


It places a 64bit length preface before the 32bit promoted string, and all works well, other than the aforementioned issues with it.

cleartext .myvar, 'string'

works a treat... but with the static_string_space in the binary, as well as my inability to work out how to get 'string',10 to work properly, heheh.

Cheers and thanks as always
Post 05 Sep 2014, 03:42
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 20451
Location: In your JS exploiting you and your system
revolution 05 Sep 2014, 06:16
If you work through the string backwards then you won't need to copy the string to a temporary buffer.
Post 05 Sep 2014, 06:16
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l_inc



Joined: 23 Oct 2009
Posts: 881
l_inc 05 Sep 2014, 11:14
redsock
As for your first issue, I totally support the revolution's suggestion.
As for the second one, just put brackets around val* in your macro header. Almost forgot: and put the directive common in front of the local directive.

_________________
Faith is a superposition of knowledge and fallacy
Post 05 Sep 2014, 11:14
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redsock



Joined: 09 Oct 2009
Posts: 435
Location: Australia
redsock 05 Sep 2014, 21:45
Hah! Sometimes the simplest and most obvious ways to solve problems are the most elusive... haha, thx very kindly to both of you...

Here is the revised macro, much nicer:

Code:
macro cleartext name*, [val*] {
common
        local .DAT,CC,I,Si,J
        align 16
        name:
        dq      CC
        .DAT:
        db      val
        CC = ($ - .DAT)
        ; create filler for the diff
        db ((CC shl 2) - CC) dup 0
        ; next up: walk backward through the string and promote it to 32bits
        I = CC - 1
        J = I shl 2
        repeat CC
                load Si byte from .DAT+I
                store dword Si at .DAT+J
                I = I - 1
                J = J - 4
        end repeat
}
    


Smile Smile
Post 05 Sep 2014, 21:45
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