Questions tagged [gcc]
GNU Compiler Collection, it includes front ends for C, C++, Objective-C, Fortran, Java, Ada, and Go, as well as libraries for these languages (libstdc++, libgcj,...).
53
questions
1
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1
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Why this x64 shellcode doesn't work?(segmentation fault)
I found a simple shellcode on the internet.
Then, to test this shellcode, I make the simple ret overwrite code.
test.c
#include <stdio.h>
#include <string.h>
char buf[100];
int main(void)...
- 55
5
votes
1
answer
124
views
Zlib structure inside a GCC static library
I'm trying to analyze a GCC static library which is a part of a commercial software.
First, I used IDA Pro to analyze entire Lib file, but it could find only object files and was unable to disassemble ...
- 151
0
votes
1
answer
292
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Output from gcc containing all included source code?
Right now, I'm using a combination of gcc -g and the objdump -S modes to generate assembly code with debug source code interleaved. However, I'm having trouble correlating some of the functions that ...
- 1,016
1
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0
answers
90
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What change to the source code would produce an LT compare rather than an OLT compare in MIPS assembly?
I need some help reverse engineering a function in MIPS assembly. It was compiled for the PlayStation 2's EmotionEngine CPU. My goal is to produce a matching decomp of the function; it is the proof-of-...
- 11
2
votes
0
answers
164
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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 ...
- 105
1
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1
answer
380
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How to locate memory address in register $esp
000011d9 <main>:
11d9: 8d 4c 24 04 lea 0x4(%esp),%ecx
11dd: 83 e4 f0 and $0xfffffff0,%esp
11e0: ff 71 fc push -0x4(%ecx)
11e3: ...
- 11
1
vote
0
answers
63
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Is disassembly of standard gcc programs trivial, or just as difficult as video game ROMs?
I am attempting to do some reverse-engineering of ARM binaries, with the ultimate goal of reverse-engineering GBA ROMs. Of course, GBA ROMs contain a mixture of code and data, so a standard ...
- 133
1
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0
answers
151
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silvio packer for shared libray leads to error: "ELF load command address/offset not properly aligned"
I'm trying to implement a packer based on silvio infection. The packer works fine for ET_EXEC. However, it failed with "ELF load command address/offset not properly aligned" error for the ...
- 81
1
vote
0
answers
69
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failed to trigger packer's loader by overwritting the entry of rela.dyn on aarch64
I have implemented packer of x86_64 shared library.
Briefly, a loader is injected to a shared library, and
the rela.dyn entry is modified such that it points to the address of the loader. Once the ...
- 81
2
votes
0
answers
229
views
How can I tell ld to link to a local symbol in a shared object?
Symbols in shared objects can be either local or global. This is controlled by a flag in the symbol table. If the symbol is local, ld won't resolve to it.
Reverse engineering can often be aided by ...
- 187
2
votes
1
answer
3k
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How to disable relro while compilation?
My doubt is how to compile the binary without RELRO? and why it is enabling FULL-RELRO when we are not providing any flags?
This is the code.
#include <stdio.h>
#include <stdlib.h>
int ...
- 33
2
votes
1
answer
276
views
Comparing the static address of the vtable of a class, to the pointer to it held by the object
I know this is compiler/ABI dependent, not necessarily standardized, etc. I've always assumed, from what I've read in several places (e.g. an answer here or the example in wikipedia), that a typical ...
2
votes
2
answers
413
views
Changing value of parameter with gdb
I have a file named exploit.c inside which:
#include <stdbool.h>
#include <stdio.h>
const char y1 = 'a';
const char y2 = 'b';
const char y3 = 'x';
const char y4 = 'y';
const char y5 = 'i';...
- 121
0
votes
0
answers
81
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 = ...
- 45
0
votes
2
answers
224
views
What is the first argument (rdi) to operator+ on x86_64 SystemV?
I'm looking through a block of disassembled C++ which works with several std::string instances. I had been confused by several calls to various versions of std::operator+, but this call seems ...
- 137
0
votes
1
answer
888
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main function not found in GCC compiled code
I'm trying to learn reverse engineering using Radare2.
For this I compiled a hello world program with GCC on Ubuntu (version: gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0).
#include <stdio.h>
int ...
- 3
0
votes
1
answer
68
views
What is the use of moving a variable 3 times only to pass it back to the original register, with no calculations in between?
I'm reverse engineering a C++ binary using IDA, and there's one function that I don't quite understand.
x = dword ptr -8
var_4 = dword ptr -4
push rbp
movss rbp, rsp
sub rsp, 10h
movss [...
- 13
0
votes
1
answer
2k
views
How to find function start in stripped binary?
Given C code, are the function addresses from the ELF the same as those in the stripped version?
I don't have any specific code in mind. Just trying to learn in general how to find the function ...
- 103
0
votes
0
answers
159
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Force gcc to use more complex instructions
I am reverse engineering a piece of assembly. I am trying to write the equivalent code in C, however, when I compile my code, gcc prefers to use simple instructions instead of the complex ones that ...
- 101
1
vote
1
answer
243
views
GCC is not recognizing symbol table in my hand-made ELF file
For learning purposes I've created (using a hex editor and some macros) the following ELF file:
hello.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped
xxd hello.o:
00000000: ...
- 11
1
vote
2
answers
350
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Detecting and solutions of stack smash protection
This video https://youtube.com/watch?v=4HxUmbOcN6Y presents how modern compilers protect stack overflows with stack cookies and function __stack_chk_fail.
How can one identify if a binary has stack ...
2
votes
1
answer
298
views
Arrangement of variables on the stack - out of order?
I was practicing some reverse engineering crack-mes as part of our university curriculum, and I have a question around the arrangement of variables on the stack.
I have a very basic C++ code, like ...
- 21
1
vote
3
answers
13k
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Use GCC and objdump to disassemble any hex to assembly code
What would be the best way (also fewer steps) to generate assembly code for a given hex code ? For e.g., if we know the architecture is x86, and given hex value 0x55, what is the best way to generate ...
- 111
1
vote
2
answers
157
views
Strings weirdly split in binary
Recently I have come across a few parts in a binary that looked odd to me, and I wanted to ask if this is something common compilers do, and if there is a way to undo it.
(The binary is from a raw ...
- 43
1
vote
1
answer
789
views
Find functions names in .init_array section in unstripped library
Is it possible to find out all instances of static initialization in a elf dynamic library.
I can dump the array of function pointers in .init_array section via objdump command like this.
objdump -s -...
- 111
1
vote
1
answer
135
views
Unknown parameters in custom signal handler on Linux
0x0000000008001946: mov 0xa8(%rdx),%rax
0x000000000800194d: lea 0x28(%rdx),%rsi
0x0000000008001951: lea 0x2(%rax),%rdi
0x0000000008001955: add $0xe,%rax
0x0000000008001959: ...
1
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0
answers
63
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GCC adds code involving `ecx` in main? [duplicate]
I have two pieces of code, one of which is compiled by me the other of which is supplied in binary-only. The code I am compiling has added instructions pertaining to ecx. What does this code do? The ...
- 1,769
1
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2
answers
6k
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Can't find the password anywhere in the binary
This is my first post here. I was recently involved in a capture the flag preparation test which involved decompiling an ELF 32-bit LSB executable, Intel 80386 file for Linux compiled with GCC. The ...
user25783
2
votes
1
answer
2k
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How to override c++ string class with LD_PRELOAD
i am trying to override predefined functions such as strcmp, getenv, etc.
i already override some of them using LD_PRELOAD options.
but i can't override string class, how can i override c++ string ...
2
votes
1
answer
317
views
What does __return_ptr do in IDA?
Let's say I have this program:
struct A {
int x;
};
struct A func1(int z) {
struct A result;
result.x = z+1;
return result;
}
int main() {
return func1(1).x;
}
When compiling ...
- 123
3
votes
1
answer
303
views
Basic hello world stack manipulation troubles
I'm a beginner in reverse engineering, and as a beginner I started to read "Reverse Engineering for beginers".
Here is the hello world program from the book (taken from chapter 3, page 12) :
Now ...
- 281
7
votes
5
answers
2k
views
How to find out if PE executable was compiled with gcc or VisualStudio?
I looked at two ways so far. Both did not convince me in regard to false positives or false negatives:
Using strings: How to retrieve the GCC version used to compile a given ELF executable?
Using the ...
- 1,540
1
vote
1
answer
1k
views
How do you compile a C program with missing symbols?
In Learning Linux Binary Analysis by Ryan "elfmaster" O'Neill. On Page 33, the author compiles a program with a symbol reference and no definition,
Let's take a look at the source code:
_start()
...
- 1,769
-1
votes
1
answer
685
views
Shells CTF segfault - wrong address
PicoCTF 2017 Shells
I have a binary and source:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#define AMOUNT_OF_STUFF 10
//TODO: Ask IT ...
1
vote
2
answers
3k
views
newbie trying to understand disassembled code
I have been writing small C programs and then disassembling them to try to understand what is actually happening under the hood.
I am using mingw-w64 on Windows 7 for my work, and I have run into a ...
- 379
2
votes
2
answers
5k
views
Changing Entrypoint in ELF executable
I wrote some code that does the following:
Searches for and finds an offset in a binary file to add code (looks for a sequence of 00s I can overwrite).
Then, I change the entrypoint of the ELF to ...
- 29
10
votes
2
answers
5k
views
What is the purpose of these instructions before the main preamble?
I wrote a small C program below:
#include <stdlib.h>
int sub(int x, int y){
return 2*x+y;
}
int main(int argc, char ** argv){
int a;
a = atoi(argv[1]);
return sub(argc,a);
}
Compiled ...
- 279
2
votes
0
answers
917
views
How can I control local variable ordering on stack in gcc?
I am writing a reversing challenge where I need to seed a bug. It's important to have a particular ordering of local variable on stack in a method. However, gcc seems to shuffle those around. How can ...
- 1,351
3
votes
1
answer
3k
views
GCC change the order of variable declaration
I have this very simple piece of code:
// test.c
int main(){
int a = 0;
char b[10];
int c = 0;
return 0;
}
Compiled with gcc (6.2.1):
$ gcc -g -o test test.c
And analysed with gdb:
$ gdb ...
- 199
1
vote
1
answer
5k
views
Passing argument through registers instead of the stack
I'm learning (and re-learning) C and assembly, and I came across a difference between what I've been taught and the actual result I have.
Some code:
int test(int a, int b){
return a + b;
}
int ...
- 199
1
vote
2
answers
1k
views
C/C++ to Assembly language
Is there any book or articles related to how C/C++ code is converted to assembly language, I mean common patterns for a specific compiler, etc?
- 95
1
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1
answer
822
views
C++ to assembly, GCC vs CL
I have following C++ code:
int main(){
int a = 1;
double d = 1.2;
return 0;
}
and get the following assembly using GCC 6.2 -m32:
main:
lea ecx, [esp+4]
and esp, -8
...
- 113
0
votes
1
answer
1k
views
Fixing weird no-sections embedded ELF binary for decompilation
I recently stumbled upon a weird binary, complied by a "Qualcomm Hexagon" compiler. The ELF binary seems fine, however section tables (section header size and string table index) seem empty. For those ...
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0
votes
0
answers
383
views
How to pass Obfuscated Elf binary to gcc optimization end
Currently I have a 2000+Line function to reverse engineer with many redundancies and appears to be obfuscated. It their a way to pass to pass this binary to gcc or clang to reassemble it and optimize ...
- 335
1
vote
1
answer
635
views
Problem to understand execution of payload (shellcode)
I know that there are lot of (good) tutorials regarding this topic, but after reading them, I really cant follow their thoughts (e.g.: Smashing The Stack For Fun And Profit):
The problem is that we ...
- 63
1
vote
1
answer
667
views
What is the difference between these two function prologue instruction sequences?
the test is on 32-bit x86. I compiled the code with gcc 4.2, optimization level o2. I compiled the C code into binary, and then use objdump to disassemble it.
Here are two sequences of instructions ...
- 2,465
1
vote
3
answers
989
views
Without push instructions [duplicate]
If I pass an argument to a function, it should be translated in assembly language into push something. I coded the following in C:
#include <stdio.h>
int sum(int a, int b,int c)
{
int ...
- 11
2
votes
1
answer
2k
views
How to get the information of "how many and which symbols are resolved by linker"?
The test is on 32-bit Linux, x86. With gcc 4.6.3 and GNU ld 2.22.
So I am trying to get the information of "how many symbols are resolved by linker" during link time? And how can I list the ...
- 2,465
3
votes
2
answers
3k
views
How can I write my main function as assembly opcodes in an integer array?
My OS is Windows 7 64-bit and my processor is an Intel Core i7-4700MQ running on the x64 architecture. My program is 32-bit.
Recently, I read an article here describing how it is possible and legal ...
- 398
1
vote
0
answers
102
views
VLAs in C++ - seemingly nonsential compiler code [duplicate]
I've been wondering, why all the hassle with variable length arrays (such as int x[n])? Theoretically, it's just another local variable, so it's merely a matter of subtracting the appropriate value ...
- 585