Sunday, July 25, 2010

New utility program: uvstructoffset

Under util/uvstructoffset/
Here and there I find the need to verify the APIs I create have the correct structure alignment. I would do this manually with something like:
printf("some_member: 0x%.4X\n", offsetof(struct my_struct_t), some_member);
But this can be automated if there was a program to parse the C code. pycparser seemed like the most convenient C parser to use. After some coding, I could transform structures:

struct sig_header_t
uint8_t dell1800FP;
short atomicForceMicroscope;
uint16_t fearAndLoathingInLasVegas;
uint8_t oatmeal;
char paperTowels;
uint16_t jointedGlasswares;
uint8_t micrometer;
int orangina;
char accidentWaitingToHappen[16];
uint8_t SATADrive;
uint16_t fastSteeringMirror;
uint32_t hamburgers;
} __attribute__((__packed__));
Into this:
struct sig_header_t
dell1800FP @ 0x0000
atomicForceMicroscope @ 0x0001
fearAndLoathingInLasVegas @ 0x0003
oatmeal @ 0x0005
paperTowels @ 0x0006
jointedGlasswares @ 0x0007
micrometer @ 0x0009
orangina @ 0x000A
accidentWaitingToHappen @ 0x000E
SATADrive @ 0x001E
fastSteeringMirror @ 0x001F
hamburgers @ 0x0021

Formatting doesn't line up on the web, but you get the idea. The C parser only parses the structure and doesn't try to guess the actual offsets. This is done with gcc since this is really the only reliable way to do it based on all of the different data types and such are considered. For decompiler use, config files will have to be referenced for data sizes and alignment.
After working with JSON, I've decided it is the sort of data exchange format I've been looking for for a while. I've never been a fan of XML because I find it overcompicated to parse and work with for general use. If I need any sort of convient data exchange between programs where performance in't an issue but convenience is, I'll probably use it as the format. As required, these can be migrated to higher performance formats. This will include configuration files and structures definitions.
Eventually I will be needing to parse out structures in the decompiled/disassembled files. Since these files don't need to be parsed often and for other data exchange reasons, I will be using the aforementioned Python parser to output a JSON structure definition.

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