Questions tagged [x86-64]

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28
votes
2answers
9k views

Why are machine code decompilers less capable than for example those for the CLR and JVM?

Java and .NET decompilers can (usually) produce an almost perfect source code, often very close to the original. Why can't the same be done for the native code? I tried a few but they either don't ...
25
votes
1answer
67k views

Reversing ELF 64-bit LSB executable, x86-64 ,gdb

I'm a newbie and just got into RE. I got a ELF 64-bit LSB executable, x86-64. I'm trying to reverse it. First I tried to set a break point on line 1 using gdb ./filename break 1 The gdb says No ...
20
votes
3answers
1k views

What are the qualitative differences in reverse engineering x64/Win64 code versus x32/Win32 code?

Many professional reverse engineers spend their days looking at 32-bit code compiled for Windows, and familiarity breeds proficiency. What are the high-level differences between reverse engineering 64-...
15
votes
3answers
9k views

Is it possible to access the higher part of the 32-bit and 64-bit registers? If so, which ones?

I don't know whether this is a silly question, but I couldn't find any answer. With the evolution of CPU architecture, register size was extended, from 8, to 16, 32, and eventually 64-bit. I was ...
12
votes
1answer
25k views

What does mov qword ptr ds:[rax+18], r8 mean?

mov qword ptr ds:[rax+18], r8 In the above code, where are we copying the value of r8 register into? I know that ds means data segment which is a segment in memory, but what does exactly [rax+18] ...
8
votes
1answer
3k views

How to investigate Windows 32/64bit (WOW64) transition

There is surprisingly little information about Windows WOW64 mechanism. I'm trying to investigate it. So when we have system call in 32-land, it calls an address that is stored in FS, which leads us ...
8
votes
1answer
752 views

Why are values passed through useless copies?

So, say that I have the following code, which gives three examples of what I believe to be unnecessary copies of values. mov QWORD PTR [rbp-0x18],rdi mov rdx,QWORD PTR [rbp-0x18] lea rax,[...
8
votes
3answers
775 views

What methodology can be used to change code flow atomically during program execution?

I have been reading a lot about the different techniques for Windows API hooking (a technique I'm particularly fascinated by and fond of), and it seems a major problem in implementing a realiable ...
7
votes
1answer
5k views

Problem while debugging with gdbserver in IDA Pro

I'm new to debugging with IDA Pro and I ran into the problem that my breakpoint is not hit while attempting to debug with gdbserver. The program is written by myself and it is simple to debug with gdb....
7
votes
2answers
2k views

32-bit binary stack layout on a x64 Linux OS

Stack layout is well documented in many ways. Especially for x86 systems as there were numerous tutorials on how to exploit stack overflow on old 32-bit systems many years ago. So far we can know ...
6
votes
3answers
68k views

How to obtain x86-64 pseudocode in IDA Pro?

Does anyone know about obtaining pseudocode for x86-64 in IDA Pro? I already tried the Hex-Rays plugin to obtain pseudocode, but when I try it, the following error pops up: "only 32bit code is ...
6
votes
1answer
3k views

ROP exploitation in x86_64 linux

I am working on return oriented programming exploitation on a x86_64 Linux. However, my research leads to impossibility of ROP exploitation in 64-bit Linux machine because all of code segments are ...
5
votes
1answer
1k views

Is IDA pulling my leg - or can REX.W sometimes not be determined in static analysis?

NB: I normally dabble with disassembly (i.e. mnemonics) and only ever look at the raw opcodes when I can't avoid it. I have the following line of disassembly of a Windows x64 kernel mode driver, ...
5
votes
1answer
3k views

xor eax, eax in x64

I have following code: sub rsp, 40 ; 00000028H lea rcx, OFFSET FLAT:$SG4237 call printf xor eax, eax add rsp, 40 ; 00000028H ret 0 Why there is xor eax, eax , ...
5
votes
2answers
260 views

Returning a C function to its grandfather

This is a homework assignment, so I'd appreciate it if I would get a hint only, not a full answer. I wrote this program which is supposed to print the following: Executing function_a Executing ...
5
votes
2answers
3k views

How many registers does an x86_64 CPU actually have?

I am currently learning reverse engineering and am studying the flags register. I had in my mind that rflags was just another name for one of the 16 general purpose registers, for example rax or rbx. ...
5
votes
3answers
2k views

IDA Pro Renaming Imports

This PE file destroys its import address table. However, all the function addresses are in this _rdata segment here: Any straight forward way to rename these functions?
4
votes
3answers
4k views

Determind length of instructions in bytes

Where is it possible to find a list of x86 instructions (and x64 instructions) with the (hex) opcode and the length/size in bytes of the instructions, such as: 0x90 = NOP = 1 byte 0xE9 = JMP = 5 ...
4
votes
3answers
437 views

What is the difference between MOV and LEA in example?

Looking at an assembly code snippet I see: lea rax, [rbp-0x50] Which tells me that the rax register now points to whatever value is in rbp-hex(50). Question. Would I achieve the same result doing ...
4
votes
1answer
161 views

rasm2 giving different output each time for x64

Disassembling is great but when trying to re-assemble to opcode it gives different results each time. Example: C:\>rasm2 -a x86 -b 64 -d "48898D80FEFFFF" mov qword [rbp - 0x180], rcx C:\>...
4
votes
2answers
1k views

Automating pattern-based de-obfuscation of x64 code using IDA plugins

Trying to deobfuscate x64 code. You can skim/skip most of this, since it mainly exists to prove I have tried and exhausted all avenues. Burning Purpose To massively automate the deobfuscation within ...
4
votes
0answers
438 views

What does this multi mov instruction do? [closed]

I came across the following multi mov instruction: mov eax, 1, 2, 3 What does this instruction do? Where can I find the correct documentation for this instruction?
3
votes
2answers
22k views

IDA cannot launch debugger for 64-bit exe files

I want to launch IDA debugger for one 64-bit exe file and it fails, have tried with more samples, but result always the same. Here is that I do. Launch IDA Pro (64-bit) Select Debugger -> Run -> ...
3
votes
1answer
553 views

What is the proper way to deal with an x86/64 instruction containing multiple prefixes from the same group?

Olly, specifically, will only accept the last prefix it finds if there are more than one from the same group. For example lock rep add dword ptr[eax],eax ; f0 f3 01 00 becomes ??? ...
3
votes
1answer
626 views

XCHG RAX, RAX: 0x09, what does this code do and how does it work?

Given the following short assembly snippet: shr rax, 3 adc rax, 0 I worked this out a bit: We know SHR sets the CF with the last bit shifted. We know ADC dest, 0 is just adding the CF. So ...
3
votes
2answers
17k views

64 bit Pseudocode decompiler

I have a 64 bit program im debugging. I found the function i need to learn more about to potentially "fix" the problem (there is no source code available for the program). To speed things up, i ...
3
votes
2answers
1k views

Purpose of NOP immediately after CALL instruction

There are a lot of ... code ... call sub_... nop ... code ... patterns in an executable dump I am working on. They appear in the middle of subroutines and I believe don't serve alignment purposes. I ...
3
votes
1answer
361 views

How can I convert this assembly code (x64) to C?

I have the following assembly (x64) function: 400700: sub rsp,0x18 400704: mov QWORD PTR [rsp+0x8],rdi 400709: cmp QWORD PTR [rsp+0x8],0x0 40070f: jne 400718 <bar+0x18> 400711: mov eax,0x0 ...
3
votes
1answer
583 views

Deobfuscating overlapping x86 assembly instructions

I'm trying to solve a reverse engineering challenge (http://crackmes.cf/users/beatrix/beaba/) and am having trouble with the obfuscation. Below is a piece of code that gets executed almost immediately ...
3
votes
1answer
202 views

How does GPROF hook to the program?

I compiled a simple helloworld and took a look at the disassembly using objdump. At the beginning there is the _init: 0000000000400600 <_init>: 400600: 48 83 ec 08 sub rsp,...
3
votes
2answers
4k views

What is an effective way to debug a 32 bits application within a 64 bits OS?

Currently I am on an x64-based system and have been doing some reverse engineering for a while. However I'm still a newbie, and the biggest issue I keep running into is the memory layout differences. ...
3
votes
1answer
360 views

IDA 7.0 - combine sequence of assembly instructions to a macro

I'm solving this CTF with IDA Pro 7.0. At some point there is an offset calculation by index, it simply multiply an index by 48 and write/read some data to it. The main problems are: the ...
3
votes
1answer
571 views

Question about the limit and base address in x86-64 segmentation model?

I'm trying to understand how segmentation works under x86-64. From what I see, it's mostly disabled, but not entirely. It looks like GS and FS registers are still using it. So I was reviewing the ...
3
votes
1answer
210 views

Unable to use CreateRemoteThread in target process

I'm trying to get a debugger attached to a malware, but it seems to pick up whenever a new remote thread is created (which makes it so I can't use Scyllahide). Even if I suspend all threads, it does ...
3
votes
2answers
360 views

How to find location of environment variables in 64 bit binaries at runtime?

In the main function, program authors can choose to receive the char * array as a parameter to main that points to the environment variables int main(int argc, char **argv, char **envp) { ... } The ...
3
votes
2answers
782 views

x86_64 Calling convention

I am slightly confused by some x86_64 linux code here (generated by llvm): # BB#0: # %entry push RBP .Ltmp21: .cfi_def_cfa_offset 16 .Ltmp22: ....
2
votes
1answer
4k views

What does lea rdx,qword ptr ss:[rbp+50] mean?

What does the code below exactly mean? lea rdx,qword ptr ss:[rbp+50] I have difficulty in rbp+50. Is rbp the base pointer in the 64 bit CPU architecture? What is the base pointer refering to? how ...
2
votes
1answer
752 views

Converting Assembly x64 code to C

I have the following code: 0000000000400526 <main>: 400526: 55 push rbp 400527: 48 89 e5 mov rbp,rsp 40052a: 48 83 ec 20 sub ...
2
votes
3answers
244 views

Is the main function's name in the symbol table of C & C++ programs always 'main'? if not, how to find the name?

So I'm trying to write a reversing tool that parses symbol table to find the main function's address right now all the binaries I'm checking the name of main function is still main in symbol table ...
2
votes
3answers
346 views

Elf x86_64 adding function

I'm trying to see if I can append function code in the .text section of an ELF while still maintaining the execution flow of the original ELF. Ideally, I want to call the new function but that's it's ...
2
votes
1answer
120 views

Windows x86 compability on x64 operating system

I know some about wow64 system, in x64 windows version, and i looked up into this wow64* dlls, to see how the actual syscall transition happen, but something i can't find, and this is probably done by ...
2
votes
1answer
7k views

64-bit integers on 32-bit machines

Let's say I create a program in C like this and compile it on a regular 64-bit desktop machine: #include <stdint.h> int main(void) { uint64_t a = 0x12345679abcdefULL; uint64_t b = ...
2
votes
1answer
52 views

Correct my understanding on a basic allocation memory

Here is the function If I understand correctly: There is a buffer of size 256 bytes created (malloc) in this buffer, the first 32 bits are set to 0 (because dword designates 32bits size) the next 32 ...
2
votes
5answers
7k views

Run PE File - (Executable) From Memory

Would be grateful for your suggestion.Trying to run a 32/64bit on (Windows 10- 64 bit /Visual studio) program which tries to run an executable from memory.This is for my learning purpose. #include &...
2
votes
2answers
2k views

Windbg x64 setting breakpoint

My issue is all about setting the breakpoint on x64 Windbg. For x86 to combine IDA and Windbg analysis nothing is required. Just copy and paste the IDA address value and it works just fine. For ...
2
votes
1answer
200 views

Why do I get e8 00 00 00 00 for all libc function calls?

I just started learning reverse engineering. The near call instruction (e8) is very confusing to me. It took me a while to figure out how address calculation works for local functions. Now I'm ...
2
votes
1answer
102 views

How are __argc and __wargv globals exported from a 64-bit PE file compiled with Visual Studio?

I need to inject my code into a 64-bit process. I'm wondering, how can I access __argc and __wargv global variables once in the injected process? Are they always present at a static/preset address?
2
votes
1answer
100 views

How to break on a window creation

in x32/x64 debugger, how can I break when a new window is opened? When inside my application, I click the "File" button in the menu bar then select "options" I want to break on that call to open the ...
2
votes
1answer
890 views

How do I denote and use JMP /5 in byte code

I'm on the OSX platform working with x86_64. I've worked out how to do near jumps with the E9 byte code directive where my relative addresses have 4 bytes (teamed up with RIP) Now I have an instance ...
2
votes
1answer
128 views

Help understanding MOVSXD

I've tried reading the documentation but the functionality of this instruction is still cloudy to me. For an example, I would like to know what is stored in RDX after these instructions: mov edx, ...