Questions tagged [c]

General purpose programming language that uses the procedural and structured programming paradigm.

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249 views

Changing local variable in caller from callee in C? [closed]

I'm implementing a function which is going to perform some time-consuming task, and I'd like to hack the benchmarking part a bit by changing the variable indicating the CPU time my function has ...
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0answers
46 views

Ghidra - search for library usage?

Using Ghidra: if library A imports library B, is there a way to search for all function calls from A into B? And more specifically: if B exports function foo, how can I find where that specific ...
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1answer
107 views

MIPS assembly to C code

I think I'm really brain-dead and am not really sure what to do next, but I am trying to manually convert assembly code to a C program. It's not really working, but I'm not sure what is wrong. I would ...
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33 views

How do I view registers at a specific point of a binary's execution?

I have a binary that I'm attempting to reverse engineer to find a flag. From using ghidra I have found that the flag is stored in the program at a point called "check" and then run through ...
0
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1answer
66 views

ret2libc: problem getting exploit work without pwntools

I am trying to exploit this program test with ret2libc. Only NX is enabled. #include <stdio.h> void vuln() { char buffer[256]; gets(buffer); } int main() { vuln(); return 0; } ...
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40 views

How to hack fan control speed?

So I recently bought a new laptop (Acer Aspire A315-57g) on which I found that the cooling solution wasn't optimal and I decided that I want more RPMs from my fan. However I wasn't able to find a ...
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0answers
47 views

Confusing objdump with data as code

I am trying to confuse objdump to solve the first exercise of chapter 6 in Practical Binary Analysis. Admittedly I am super weak with inline assembler but I made a best-effort attempt and tried to get ...
0
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1answer
51 views

string pointer to byte conversion condition

I am trying to understand the following snippet. I understand that the first check would check if it is even if it would be an int, but I don't understand it in this context. Could someone explain to ...
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1answer
485 views

Reverse engineering android native packer

im trying to Reverse engineering an android app and the app have 4 folders in the /data/data/{package} folder ├───app_dexprotector │ 823517D25836B88F1C499C02370A047E.dat │ ...
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1answer
87 views

How to get the input necessary to get to the end

In short, I have a code that gets an input via stdin. Once it has the input string in memory, it verifies its integrity by calling a function for every condition, and exiting the program if those ...
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2answers
116 views

Using a buffer overflow to call a function

I'm new to reverse engineering C binaries but have been working on an old ctf and thought to ask for explanation of specific assembly commands and how a buffer overflow might force a function to be ...
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0answers
46 views

How to maintain function ordering in an executable when replacing machine code with C step by step?

I am working on reversing a DOS game consisting of 16-bit MZ EXE files. I was able to determine the exectuables were generated by Microsoft C v 5.10, and loading the signatures from the static ...
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0answers
79 views

How to create an algorithm in C...(or C# or C++, basically in "a programming language")

After a LOT of sending challenges and recording the responses I've 'broken' the "encryption" in my car's immobiliser...the reason for doing it is so I can use the engine and transmission in ...
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0answers
34 views

How do I disassemble mips .o object files in ida elf 64bit

So I’m trying to disassemble some object files in mips. I use IDA 7 on windows. These object files are loadable kernel modules. Mipself64 Is What ida auto sets to when they are dropped in. I’d like to ...
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1answer
102 views

How do I find missing/undefined vtable functions in IDA64?

I'm reverse engineering a game and came across some function calls like the ones shown below, how do I find where these functions are located / decompile them? (*(BaseClient->int640 + 304))(...
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0answers
50 views

Trying to call the Exit Shellcode in a c program

#include<stdio.h> #include<stdint.h> char shellcode[] = "\xb8\x3c\x00\x00\x00" "\xbf\x14\x00\x00\x00" "\x0f\x05"; int ...
2
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1answer
131 views

Extracting strings from binary files (.exe)

This question has been asked quite a lot especially on stackoverflow, but the solutions/replies are not clear or extensive. What I`m looking for is to build what Strings does from Sysinternals. My ...
3
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1answer
49 views

Confused about the use of the shl instruction in this disassembly

I created a code construct in C to see how it looks in x86. I'm confused about the use of the shl instructions. I'm confused about what is happening in between the lines <+39> and <+51> I ...
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2answers
77 views

Import header files in IDA to get the struct definitions?

I am reversing a program that has a lot of internal structs in it. The problem is that there are a lot of structs, so i can't import them manually using local types->insert. Lets say i have some ...
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36 views

How to reverse engineer structs in radare2?

Is there any way to indentify structs in radare2? when i tried to look them, they look like normal variables, i seen people using td and tl command but I don't know how to use them. If you know please ...
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0answers
56 views

Radare2 is showing weird disassembly as compared to disassembly of gcc

Today i was playing around with c code in r2. I compiled a file which had the following code. #include <stdio.h> int main(){ int a=9; float b=1.1; int sum; sum = ...
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1answer
76 views

Why compiler is doing this?

While I was disassembling my own C code for practice I saw an interesting point which I want to share with you guys and needs to know the answer as I always get from here. Now, the interesting point ...
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1answer
136 views

Arrays assembly

I'm reversing my C array's programs where I'm storing numbers in arrays like this... int marks[5]; marks[0] = 1; marks[1] = 3; marks[2] = 2; marks[3] = 7; marks[4] = 9; so the compiler showing me the ...
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3answers
264 views

How to extract machine code from a file(especially executable) in C

How to get machine code of a file(mainly executables) in C? I have written a C program to convert machine code to assembly. But how to get machine code of a file? How would I go about programming a c ...
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1answer
101 views

Not able to understand the C-switch statement in disassembly

While I'm trying to disassemble my own C code I am stuck in a problem of not understanding how this Switch statement is implemented in assembly code. Can anyone please help to figure it out? This the ...
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0answers
28 views

HexRay API - Programatically rebaseing program on firmware

I am working on several firmwares (mostly ARM and PPC) that have no structure that IDA can decipher and so far I have been guessing BASE address until the functions and strings align with what I see ...
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1answer
62 views

How to simplify a function "calling itself's reference"

I encounter often a function calling itself (in the pseudo code) such as: result = (**(__int64 (__fastcall ***)(volatile signed __int32 *))lambda)(lambda); Since the disassembly is call qword ptr [...
4
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1answer
186 views

Find Decryption algorithm of an encryption algorithm

I recently work on an algorithm that encrypt some data with 8 byte length. I worked hard and I successful to get this algorithm, but I need decryption of this algorithm. How I can invert it? I guess ...
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1answer
219 views

How to restrict angr to printable characters

I have a binary that scanfs and then does some checks and returns either FAIL or SUCCESS that has SUCCESS for multiple inputs. Although only one of the inputs has only printable characters. How do I ...
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1answer
422 views

winmain reversing the assembly to c code

this is I got so far #include <windows.h> int WinMain(HINSTANCE hlnst,HINSTANCE hPrev, LPSTR lpCmd,int nShow){ int k =0; int j= 0 ; MessageBox(0,"crackname","",0); int i; ...
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1answer
46 views

Reverse engineering mode X VGA function(s)

I'm trying to reverse engineer an old DOS game. At the moment I'm stuck at a function that implements some functionality of VGA running in mode X. My issue is that any of the available sample codes on ...
0
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1answer
54 views

Assuming x is a number smaller than 0xff what happens to x after the assignment LOBYTE(x)=x-1?

I understand that LOBYTE is an IDA macro for retrieving the lower byte of a variable. My question is what is the difference between the result of x=x-1 and LOBYTE(x)=x-1 when x is smaller than or ...
24
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4answers
14k views

Can I create an object file using gcc that cannot be reverse engineered?

Is it possible to create an object file using gcc that cannot be reverse engineered to its source code ?
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1answer
65 views

Link decompiled C code to Assembly (retdec decompiled object into C code, but with many errors, i found the kill switch which i need to edit)

I am using retdec to decompile a piece of software. It has a "kill switch" to detect if it's being run in an untrusted environment, in the decompiled code it just a simple if (env_untrusted()...
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1answer
51 views

Call libc functions from the payload statically injected into ELF binary

I am working on ELF-injector, which given some payload (currently it's an assembly file with .text section only) will inject it into ELF binary. I had related post here. Now I would like to make it ...
0
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1answer
39 views

Visual c compiler options

I ask if exist some c compiler option that can "keep" some imformation after compile that can be visible when I disassamble with IDA. This because I need to find a particular funciton with ...
1
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1answer
128 views

how could i follow a system call from a dll -> kernel driver syscall

basically i would like to follow (system calls / internal calls) that basically lands in the kernel i would like for example to debug a specific dll ex : ntdll.dll and follow it to (NtXXX) function ...
45
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8answers
31k views

How do I add functionality to an existing binary executable?

I want to add some functionality to an existing binary file. The binary file was created using gcc. Do I need to decompile the binary first, even though I sufficiently understand the functioning of ...
2
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1answer
2k views

Basic Buffer Overflow Help

I am currently practicing for a CTF competition and one of the practice challenges is a buffer overflow exploit. Before this challenge I knew absolutely nothing about these exploits, but I've been ...
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1answer
1k views

what is best forum to ask about hex reversing? [closed]

i want to create c script extract encrypt package. just can open it in hex editor to view and need knowledge and technique for write script for extract it. Script will work in command-line ( window 10 ...
4
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1answer
326 views

ELF binary injection

I am currently working on an ELF-injector and my approach is standard: find code cave (long enough sequence of 0's), rewrite it with the instructions I want to execute and then jump back to the start ...
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0answers
95 views

How the return address of the notesearch program was calculated in "The Art Of Exploitation"

I am reading the book "The Are Of Exploitation" 2nd Edition by Jon Erikson and there is something I don't understand about the calculation of the return address. In page 137 it covers the ...
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0answers
103 views

Delphi mt38 CRC (Tricore 1766 Arch)

I want to calculate CRC32 for Delphi mt38 and found the below assembly algorithm and converted it to C. It seems that this algorithm is defined for n = 256 or 1024. I want to calculate CRC32 for n = ...
2
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2answers
110 views

Newbie problems exploiting a format string vulnerability

I encountered a print format vulnerability challenge in a CTF. I don't know anything about these vulnerabilities, so I'm working my way through Saif El-Sherei's format string exploitation tutorial ...
0
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1answer
101 views

Converting rep movsd to to C without memcpy

So I am currently in the stages of creating binexact version of functions in decompiled code. I noticed that in this function the rep movsd is called and logically this is translated as Qmemcpy/memcpy ...
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1answer
61 views

Custom IDA Decompilation Format

Is there a way to customize the format of IDA's decompiled code? e.g. char buf[7]; // [rsp+5h] [rbp-1Fh] to char buf[ 7 ]; // [ rsp + 5h ] [ rbp - 1Fh ] or switch (c) to switch( c )
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2answers
387 views

how to use class member function defined in a exe within a dll

I have an executable (.exe) containing some classes and functions definition and plan on using those functions from within a DLL, although I know to call a regular C style function using calling ...
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0answers
161 views

Binary bomb lab, can't find starting number and having problem recognizing pattern

The following is the assembly dump of a binary bomb from bomb lab Basically, you have to come up with a 6 number sequence to defuse the bomb, however, I am having trouble finding the first number and ...
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4answers
138k views

Converting assembly code to c

I have the following assembly code over Linux distro: # using the .data section for write permission # instead of .text section .section .data .globl _start _start: # displaying some characters ...
2
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1answer
136 views

Why can't find hardcoded string in the disassembled program?

I've wrote a simple program to print something on the screen as below: ebra@him:/tmp/tuts$ cat sample.c #include <stdio.h> int main() { puts("Sample!"); } ebra@him:/tmp/tuts$ ...

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