Questions tagged [c]
General purpose programming language that uses the procedural and structured programming paradigm.
316
questions
2
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0
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75
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What hints can x86 disassembly give as to GCC/G++ compiler version and options?
I've taken an interest to disassembling binaries and attempting to recreate 1:1 source code (logic) in C and C++ compiled with GCC. I say "logic" because this question does not pertain to ...
1
vote
1
answer
76
views
C instruction causing an address shift
I am trying to recreate a segment of assembly back into the C code. Below is the progress I've made so far, but I'm getting stumped on a specific section.
00000000000010049 <mysteryFunc>:
...
- 13
1
vote
1
answer
66
views
Why is Visual Studio compiling my EXE file with an entry point that is not in the file?
So I am trying to open my test app EXE file in ollydbg to study the assembly, the stack, registers and all that stuff for educational purposes and it gives me this message saying that the entry point ...
- 11
0
votes
1
answer
75
views
Crackmes challenge not validating all answers
I am playing with this crackme. The executable takes a numerical input (e.g., 123) and adds all the numbers. The total must be 50. However, I noticed that not all inputs adding up to 50 are validated. ...
1
vote
1
answer
59
views
Custom IDA Decompilation Coloring
Is there a way to customize the coloring of IDA's decompiled code?
IDA -> Options -> Colors -> Syntax doesn't seem to affect the coloring of decompilation.
- 113
2
votes
2
answers
393
views
Understanding a C code including CRT functions, decompiled with Ghidra
I am trying to learn software reverse engineering with Ghidra, though I have never used Visual Studio Compilers or the C runtime (CRT). I have a piece of decompiled C code:
<typeName> <...
- 159
0
votes
0
answers
16
views
Print CMarkupSTL object with GDB
CMarkupSTL is contain XML. How can I print that XML with GDB while I debug process?
I run on Arm Linux
1
vote
2
answers
145
views
Is it possible/feasible to decompile a program written in C++ to C?
I've not seen a lot of material on this. I've seen people attempting to bring a C++ program back to C++ code, and claiming how hard it is, but C code from C++ program? I don't know.
If it is possible, ...
- 21
0
votes
2
answers
184
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Reversing an obfuscation through a long linear switch statement
I have a program (ELF, 32 bits) that is probably quite short and simple, but which have been obfuscated with the following construction:
i = 0
switch(i):
case 0:
one small instruction
...
- 11
1
vote
1
answer
359
views
How to define "code" variable type in Ghidra
Of all the confusing parts of Ghidra, I'd like to ask about the "code" keyword. A similar question was asked here. However, I am not asking what the keyword is, but how to interpret/define ...
- 21
0
votes
0
answers
68
views
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, ...
- 101
1
vote
2
answers
214
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 ...
- 111
0
votes
0
answers
36
views
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 ...
- 1
0
votes
0
answers
85
views
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, "...
1
vote
0
answers
30
views
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 ...
- 11
0
votes
2
answers
77
views
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 ...
- 103
1
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0
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168
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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 ...
- 111
2
votes
1
answer
101
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 ...
- 23
2
votes
1
answer
290
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?
- 145
0
votes
1
answer
52
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;
// ...
} ...
- 145
0
votes
1
answer
242
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 ...
- 1
0
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0
answers
103
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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 ...
- 101
0
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0
answers
67
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
votes
1
answer
200
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;
}
...
- 33
1
vote
0
answers
103
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 ...
- 383
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0
answers
101
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 ...
- 111
0
votes
1
answer
63
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 ...
- 3
2
votes
2
answers
239
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 ...
- 21
1
vote
2
answers
320
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 ...
- 113
0
votes
0
answers
52
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 ...
- 101
0
votes
1
answer
169
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 ...
1
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0
answers
87
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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vote
0
answers
64
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 ...
1
vote
0
answers
65
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 ...
- 11
2
votes
1
answer
434
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 ...
- 141
3
votes
1
answer
91
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 ...
- 67
0
votes
1
answer
140
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))(...
- 11
0
votes
2
answers
716
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 ...
- 320
0
votes
1
answer
137
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 ...
- 25
0
votes
0
answers
64
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 = ...
- 25
1
vote
1
answer
163
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 ...
- 323
0
votes
1
answer
89
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 ...
- 323
2
votes
1
answer
203
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 ...
- 323
0
votes
3
answers
605
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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0
votes
1
answer
79
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 [...
- 123
4
votes
1
answer
208
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 ...
- 87
0
votes
1
answer
53
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 ...
- 57
0
votes
1
answer
73
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 ...
- 257
0
votes
1
answer
106
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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()...
0
votes
1
answer
101
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 ...
