Re: [DynInst_API:] Wrong memory write size?

[John Detter <jdetter@xxxxxxxx>]

Fredi,

Could you provide me with your GCC version? I'm looking into your issue now.

Sorry for the long wait,

-- John

On 7/10/2016 5:10 AM, Frederik Peukert wrote:

Hi all,

 

I use getMemoryWriteOperands() to get the _expression_ of Operands that write to memory and size() to get the actual size of the write. However, it always returns 4 byte, even if I write a single byte (char) like in the following program.

 

int main(void) {

   char x = 'A';

   return 0;

}

 

Even gdb disassembles it to a byte sized write: “mov BYTE PTR [ebp-0x1], 0x41”.

I know that EBP is a 4 byte register, but a 4 byte write would just overwrite the variable next to “x” (at least if layout is not 4 byte aligned). Tell me if I am wrong.

I am using a 32-Bit Linux mint (vmware) and Dyninst 9.2.0.

 

Relevant code:

 

int main(int argc, const char** argv) {

                BPatch bpatch;

                BPatch_addressSpace *app = bpatch.openBinary(“MUTATEE”, true);  

                BPatch_image *appImage = app->getImage();

 

                BPatch_Vector<BPatch_function *> functions;

                appImage->findFunction("main", functions);

 

                BPatch_function* f = functions[0];

                BPatch_flowGraph* fg = f->getCFG();

 

                std::set<BPatch_basicBlock *> blocks;

                fg->getAllBasicBlocks(blocks);

 

                for(auto bb_iter = blocks.begin(); bb_iter != blocks.end(); ++bb_iter){

                                std::vector<Instruction::Ptr> insns;

                                (*bb_iter)->getInstructions(insns);

                                for(auto ins_iter = insns.begin(); ins_iter != insns.end(); ++ins_iter){

                                                cout << (*ins_iter)->format() << endl;

                                                if((*ins_iter)->writesMemory()){

                                                                std::set<_expression_::Ptr> memAccessors;

                                                                (*ins_iter)->getMemoryWriteOperands(memAccessors);

                                                                if (memAccessors.size())

                                                                {

                                                                                for(auto it = memAccessors.begin(); it != memAccessors.end(); ++it)

                                                                                {

                                                                                                std::cout << "\tmem write (size: " << (*it)->size() << ")" << endl;;

                                                                                }

                                                                }

                                                }

                                }

                }

BPatch_binaryEdit *appBin = dynamic_cast<BPatch_binaryEdit *>(app);

                appBin->writeFile(“MUTATEE_PATCHED”);

 

                return 0;

}

 

Thanks!

 

--Fredi

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