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Index > Windows > Simple compare and patch generator+patch programme

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bzdashek



Joined: 15 Feb 2012
Posts: 147
Location: Tolstokvashino, Russia
bzdashek
Good evening,

While experimenting with assembler, I ran into a problem of comparing two files of equal size. The "original" and "patched" version.

I wrote two simple programmes in order to do that:
1. fcompare - compares 2 files and writes the result to the *.fcp file.
2. fcp - opens the *.fcp file, searches for original programme with human help, and then turns it magically into fixed version.

I reused the error reporting technique that Tomasz used in FA.asm and some code regarding file operations from fasm\TOOLS\WIN32\SYSTEM.INC.

Structure of *.fcp file:
Code:
4 bytes - signature
2 bytes  - file version
2 bytes - number of entries
4 bytes - original file size
2 bytes - file name length
1..260 bytes - target filename
--- end of header ---
;1 entry
4 bytes - offset from the start of file
1 byte  - original byte
1 byte  - patched byte
....
;n-th entry
4 bytes - offset from the start of file
1 byte  - original byte
1 byte  - patched byte
--- end of file ---
    

Size of Entry - 6 bytes
Maximum number of entries in *.fcp file is 65536.

Hence, maximum *.fcp file size is 14 + (1..260) + 65536*6 = 393230..393489 bytes.

The limit for size of patched file to compare is 100 Mb. Programme reads the whole two files into memory, that might be bad practice, I did consider using 64k blocks for compare procedure, but I was lazy to implement it.

I tested it on number of files, but I might have missed some bugs, so it would be wonderful if you could report bugs in this thread. Or you can fix them yourself. Smile I'm attaching full sources.

I know I'm not the first to write such thing, but I want to hope that it will be useful for the ASM society.

Thanks for your attention.


Description: File Compare & Patch
Download
Filename: fcpatch.7z
Filesize: 8.59 KB
Downloaded: 96 Time(s)



Last edited by bzdashek on 09 Apr 2012, 08:39; edited 1 time in total
Post 08 Apr 2012, 21:00
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typedef



Joined: 25 Jul 2010
Posts: 2913
Location: 0x77760000
typedef
One way also is to use the hashing technique. Very Happy
Post 08 Apr 2012, 21:38
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shutdownall



Joined: 02 Apr 2010
Posts: 518
Location: Munich
shutdownall
I would sell this program to Microsoft. For the next patch day. Laughing
Post 08 Apr 2012, 23:51
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bzdashek



Joined: 15 Feb 2012
Posts: 147
Location: Tolstokvashino, Russia
bzdashek
This is the standalone patch generator. You compile it specifying a file include directive @ patch_data label (see source). After that patch file is included in exe. You can distribute it afterwards, for example.

At first I tried to combine them with copy /b, but when programme starts, windows loads just what is specified in the header of EXE file. I was lazy to dig the PE specification.


Description: File Patch
Download
Filename: fp.7z
Filesize: 2.06 KB
Downloaded: 103 Time(s)

Post 14 Apr 2012, 21:48
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