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sub_123434 proc near 
mov esi, [ebp-1Ch] 
sub_123434 endp

What means proc near? Can someone possibly explain also the whole function?

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Insofar as proc and endp, start here. A good explanation for nearcan be found from this document, which states as follows:

Attribute is NEAR if the Procedure is in the same code segment as the calling program; or FAR if in a different code segment.

The meat of the code is this:

mov esi,[ebp-1Ch]

This bit of code is moving a value from the stack into the esi register. Depending on the compiler used and context, you might stand to glean additional information from register conventions where a value being moved into the esi register is concerned. More specifically, consider the accepted answer from this post.

Also, ebp- (as opposed to ebp+) is a typical sign of arguments that have been passed to a function--of which those values reside on the stack within memory addresses that can be referenced as long as that particular stack frame exists.

Regarding [ebp-1Ch], that's a pointer. In this case, the ebp register contains a memory address (or, more specifically, the value in ebp is treated as a reference to a memory address instead of a literal value), and -1Ch is an offset from that memory address. The lowercase 'h' is just a pneumonic meaning "hex," and to that end, you might also sometimes see offsets and/or hex-based values referenced with a preceding 0x, like this: [ebp-0x1C]. Bearing that in mind, you can really think of that as [ebp-1C].

Do note that ebp and [ebp] are different things. [ebp] means the value inside of ebp is treated as a reference to a memory address. Let's assume ebp has 0xD34DC0DE in it. Now consider the following:

mov esi,ebp
mov esi,[ebp]
mov esi,[ebp-1C]

The results of each of these would be the following:

mov esi,ebp // esi now contains the literal value 0xD34DC0DE

mov esi,[ebp] // esi now contains whatever is inside the memory address 0xD34DC0DE

mov esi,[ebp-1C] // esi now contains whatever is inside the memory address 0xD34DC0C2 (which is 0xD34DC0DE - 1C)

Overall, it looks like that subroutine isn't doing anything but moving data from the stack into a register. As a completely blind assumption, if we assume that each argument passed to its respective function is 4-bytes wide, then [ebp-1C] references the 8th argument passed to perhaps a parent routine of this subroutine. In this case, other values of interest could potentially reside in [ebp], [ebp-04], [ebp-08], [ebp-0C], [ebp-10], [ebp-14], and/or [ebp-18].

Ultimately, we're lacking context here to gather what the purpose of this function you've provided is--though, again, a combination of the aforementioned conventions can possibly tell you a lot about what that mov instruction is potentially a part of. Look into calling conventions for additional clarity. You should be able to infer and research the rest based on the information herein.

| improve this answer | |
  • @Yoonisj: please post a new question about that and provide relevant code snippets – Igor Skochinsky Jul 26 '17 at 9:00
  • call ds: RegOpenKyEx call ds: RegEnumKey mov edi,ds:RegCloseKey what this malware do in this function, if these three function are below each other – Yoonisj Jul 26 '17 at 9:01

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