Questions tagged [c]

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

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What is this CRC32 algorithm (written in C), and how can it be written in Java or Python?

I've been trying to convert this CRC32 algorithm to Java or Python, but I haven't been successful, I believe it's because I'm not familiar enough with c. Note that I believe DAT_804818d0 is the seed, ...
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80 views

is there a tool to decompile old exe to C?

I follow the free software implementation of OpenRCT2 from the beggining (when it was in other repository). And the first commits are a bunch of C files, these files has a lot of asm blocks of code ...
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Unable to redirect program because function address is not correctly written to the heap

I have a heap overflow example program (heap0.c)compiled as follows: gcc heap0.c -w -g -no-pie -z execstack -o heap0 In order to overwrite the instruction pointer with (BBBB = \x42\x42\x42\x42), I ...
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How can i read offset from branch opcode of thumb mode

I have a function that can make a branch opcode: uint32_t JMPCode(uintptr_t func, uintptr_t addr) { uint32_t code = ((addr-func-4) >> 12) & 0x7FF | 0xF000 | ((((addr-func-4) >> 1) &...
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Injecting class into the JNIEnv in android jni

void *handle = dlopen("/data/local/tmp/libnative-lib.so", RTLD_LAZY); if (!handle) { printf("\nFailed to load library\n"); } void *offset = dlsym(handle, "...
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Make avaible x64 C++ exceptions on manually mapped module

I am trying to bind Lua on manually mapped module. As you can see clearly on here. They are using C++ or C exceptions on their API and there is no way to avoid them. I wonder to know if there are ...
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Understanding Loop Statements: For & While [closed]

Background Hello! New user. I am working on a personal computer science project that involves research on loop statements such as the for and while loops in C - these loops can apply to other ...
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82 views

What is happening with this *param_1?

I am a bit of a starter, so bear with me as I can't find the answer through Google (a common thing in Ghidra work I noticed so far). I have a function that seems to read like it is a Constructor. But ...
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1answer
92 views

Useless instructions in a compiled getter

This is the second time I see this kind of function today : .text:00000000000010B0 sub_10B0 proc near ; CODE XREF: sub_1120:loc_1143↓p .text:00000000000010B0 lea ...
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1answer
179 views

Is there a way to name a flag for a bit field in Ghidra?

In a line like this: if ((my_variable & 0x80000000) == 0) { Is there a way to label 0x80000000 as e.g. FLAG_HAS_PROPERTY_GREEN, or would I have to rely on comments for that?
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45 views

Does psVar[-6] refer to 6*sizeof(psVar) bytes before psVar? Can you avoid the negative index?

In this decompiled code, does psVar8[-6] refer to 6*sizeof(psVar8) == 12 bytes before psVar8? psVar8 = (short *)(&DAT_1412345b4 + named_index * 0x20); do { if (psVar8[-6] == 0) break; // ... } ...
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123 views

Translate ASM code x86 32 bits in C

I have a exercise which i can't resolve it, and i need help. If anyone can help me it would be great. I have the next ASM code in x86 32 bits which i need to translate in C language: Dump of assembler ...
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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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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 ...
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132 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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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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80 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 ...
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1answer
59 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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2answers
179 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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2answers
141 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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49 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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1answer
114 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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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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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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57 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 ...
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1answer
211 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 ...
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1answer
69 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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1answer
115 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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2answers
267 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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61 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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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
147 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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1answer
84 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
154 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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3answers
427 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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35 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
68 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 [...
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1answer
193 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
49 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 ...
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1answer
62 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 ...
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1answer
83 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
59 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 ...
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1answer
49 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 ...
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1answer
505 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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127 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 = ...
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1answer
146 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
68 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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1answer
159 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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1answer
84 views

Why I get 0xc00000005?

I'm trying to use RunPE technique (For learning). First, I tried it on Windows XP(32-bit) and no error occurs but, the injected code for(HelloWorld) didn't run. Then, I tried to use it on Windows 7 ...
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68 views

Reverse an encryption algorithem in APK .so file

I try to reverse a cipher algorithm (I guess Tiny Encryption Algorithm (TEA)) in an android application. But I have a serious problem in initializing arguments. How I can understand that I have ...

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