Questions tagged [arm]

A family of instruction set architectures based on a RISC architecture developed by British company ARM Holdings. Heavily used in embedded devices such as mobile phones, tablets, set-top boxes, ...

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264 views

Need help understanding XOR cipher

I am trying to modify a save file for a game. I think it is using an XOR cipher to encrypt it. Looking though the disassembly I think I found the function that decrypts it. I ran the assembly ...
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1answer
439 views

ELF - The start address of .got section is different from the entry point address of the GOT(global offset table)

I used readelf to read the information of the ELF file. I found the address of .got section in the section header is different from the GOT entry point address read from the dynamic section. Is the ...
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2answers
201 views

Reverse engineer a ARM-v7a function

Currently I am trying to reverse engineer the following armeabi-v7a function: I already wrote the following Java code: static double getFunc(double param0, double param1, double param2, double ...
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Disassemble ELF - PC is set to 0?

I tried to disassemble a ELF file which is a shared object file executed on armv7a (Android). I saw a strange block. It seems that the PC, program counter register, is set to 0. Did I miss something ...
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1answer
651 views

Finding RegisterNatives function calls in JNI_OnLoad's assembly code

My goal is to see what a native method m does. It doesn't have a direct counterpart in the so file, but I've found the JNI_OnLoad function's ARM assembly code. It starts with AAAAAAAA <JNI_OnLoad@@...
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762 views

How to Modify this Branch in ARM64?

I try to modify the branch of this disassembly in a binary: SUB SP, SP, #0x60 STP X26, X25, [SP,#0x50+var_40] STP X24, X23, [SP,#0x50+var_30] STP X22, ...
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1answer
121 views

Could someone explain how this ARM instructions works compared to the actual Objective-C code?

I'm trying to understands how it works by decompiling my own Objective-C code. Here's the decompiled instruction: var_8= -8 var_4= -4 SUB SP, SP, #8 MOVS R2, #1 STR ...
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0answers
394 views

Patching an ipa (iPhone app) using Hopper Disassembler

I have learned in the past to patch some iOS apps to bypass jailbreak detection. Today, I decided to change the UI elements in the Spotify app on iOS Platform (ios 11). I downloaded a .ipa file of ...
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1answer
170 views

Which ARM command is influencing the SP position?

I do static analysis of ARM assembly code (I can't debug it). When I look on argument that in SP+0x<SomeOffset> I can find what I'm looking for, but if I look a few lines further down I see ...
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1answer
89 views

Why would an ELF SHT_REL section contain relocations outside the section its sh_info refers to?

I have a .so from an Android JNI/NDK application. Here are two of its sections: [Nr] Name Type Addr Off Size ES Flg Lk Inf Al [10] .rel.plt REL ...
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2answers
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How can I make sense of an Android NDK library?

So I'm currently trying to understand how an Android app interprets the data sent from a Bluetooth-enabled scale. Understanding the Java code was relatively easy. The code was obfuscated but I found ...
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1answer
4k views

Why is this ARM binary throwing an 'Illegal instruction' error and quitting?

Issue I'm hoping someone can help me determine why this binary won't execute. It is a closed-source, stripped ARM binary. That said, it is freely downloadable on the internet so there is a link to ...
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2answers
145 views

ARM Thumb2 register usage

I am reversing ARM Thumb2 code. I am looking for a table that shows which registers are used to pass arguments to functions, and which registers must be saved after the function ends. By the way, if ...
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1answer
708 views

How to write [sp+local_variable] in radare2

Hello I'm playing with my native android library, everything was going smoothly till now. I have problem with opcodes, i don't know how to tell radare2 to write str opcode with specifc registry, and ...
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1answer
348 views

how to understand branch arm instruction

I have this instruction F6F700B8 I know that it b #-0xA000 but how I can understand from F6F700B8 that is b #-0xA000 ? . When I tried to translate it on http://armconverter.com/hextoarm/ I get B.W #...
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544 views

Best Way to Identify Statically Linked Functions in Firmware

I have a piece of firmware that I pulled off an NXP LPC17XX series chip. Through reviewing the processor manual, I was able to identify the entry point of the code and disassemble the code without any ...
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1answer
62 views

Ldr arm thumb2 must be multiple of 4?

I saw here http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0489c/CIHDGFEG.html that on arm thumb2 ldr must be multiple of 4. I run on arm thumb 2 and want run this instruction ldr r0, ...
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658 views

translate arm instructions to hex

I looking for simple tool(not site) to translate arm instruction to hex like http://armconverter.com/. Without linker , I want put 1 instruction , and want get the hex . Do you know one please?
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1answer
560 views

Determining endianness of PE files (Windows on ARM?)

For ELF files, there is a field near the start of the ELF header that indicates the endianness of the file:e_ident[EI_DATA]. If an application wants to extract data from the header of a given ELF ...
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1answer
209 views

Arm function save registers r0 and r1

I see arm 32 bits assembly code. Usually each function do push { r4-r9,lr} ( save 6 registers on stack ). And in the end of function pop them . I see function that save push {r0,r1,r4-r9,lr} but ...
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2answers
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Edit arm thumb2 intelhex file

I have intelhex file to arm 32 bits thumb 2. I want edit this file add/ change instructions. Looking for easy and free tool (prefer gui windows tool ) to do it please.
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1answer
418 views

How ida choose arm Thumb/Thumb2

I load binary file to ida and choose arm cpu. How can I see if ida choose on arm/arm Thumb2 / arm Thumb? and how can I change it? Bytes translate is depend witch arm is it(arm/arm Thumb2 / arm ...
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2answers
396 views

Arm ldr diffrent between # and =

In ARM assembly, what is the difference between ldr r4, =0x44454433 and ldr r4, #0x44454433 ?
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1answer
481 views

Patching branch on assembly code

I compile this code 1. #include <stdio.h> 2. void F(int a, int b) 3. { 4. int c= a+b; 5. int d= a*b; 6. } 7. void printAll() 8. { 9. printf("test1"); 10. printf("test2"); 11. ...
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682 views

explain c compile code

I compile c code to arm with this site https://godbolt.org/ int F(int a, int b) { int c=0; for(int i=0;i<=10;i++) { c+=a+b; } return c; } the result was F(int, ...
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1answer
115 views

Newbie here: hidden values in assembly? [closed]

So i'm new to the whole reverse engineering thing with only experience in C#. So I wanted to try and change the framerate of applications (eg. this unity game) at an assembly level on iOS ( I have an ...
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3answers
5k views

What is an immediate value?

I just read this post. What does mean an "immediate value" ? Is there any string/ascii there? How can I find this value on the binary file? I have the same code and when I search on 0x28 address I ...
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3answers
5k views

How does the ldr instruction work on ARM?

ldr r0, #0x28 What does thw ldr instruction ? Does it load a string from some offset? How can I find the string/value that is actually loaded ?
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1answer
376 views

Undefined instruction in Go binary compiled for ARM

I'm reverse engineering an ARM binary written in Go, and the following code sequence occurs fairly often (from runtime.cgoIsGoPointer): BL runtime.panicindex DCD 0xF7FABCFD or, from runtime....
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1answer
471 views

Binary encryption

I'd like to ask your help to understand the algorithm used to encrypt these hex/bin firmware (for an ARM-Cortex M4 microcontroller). In the tar file above you can find different firmware versions. ...
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0answers
1k views

Arm hex firmware reverse

it has been a couple of months that I'm working on the firmware produced by a company that makes (not licensed) gamepad console adapters. One of my goal was to understand how they bypassed (hacked) ...
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1answer
567 views

How to change a string in a arm 32bit lsb executable binary using radare2?

I have a arm 32bit lsb executable which prints "hello world" to the screen. How do I change the string to "Good bye" using radare2. I believe this will teach me the basics of RE and radare2. Thank ...
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2answers
1k views

How can i start the RE process in radare2?(make changes to the registers) [closed]

I'm an absolute newbie to reverse engineering. I have a 32bit lsb arm binary which I would like to reverse engineer using radare2. How should I begin ?
2
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1answer
319 views

Hex-Rays function signature does not match demangled name

From the demangled name, I know that a function takes an std::string const& as a parameter but when generating psuedo-c code with Hex-Rays' decompiler it autodetects the parameters as (int a1, int ...
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1answer
156 views

ARM function start points look strange sometimes in IDA Pro

I am a little bit confused with this strange issue with ARM firmware. My original firmware file has no symbols, so I need to find them by myself trough the internet. But here I have a certain function ...
2
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1answer
2k views

Entry point for STM32 firmware

I'm trying to disassemble a firmware for a DIY project, open hardware but closed firmware. My question is how to initialize the disassembler properly (Hopper Disassembler). The values I try to figure ...
2
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1answer
106 views

ARM system crashes after changing stack address

-- Edit with latest update on the problem, it is not solved yet :( -- While playing with an ARM embedded Linux system (Version 3.8.13), out of curiosity, I created a small "debug" kernel module. ...
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2answers
5k views

ARM64 syscalls table

I wonder if there some syscall table for Linux ARM64 architecture? I found syscall table for Linux ARM32 and many other architectures, but the problem still exists. Does anyone know where can I find ...
2
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1answer
3k views

Inject code into JNI function (Android shared library)

An android app loads a native library (.so) using System.loadLibrary. It then calls a specific function, which takes 3 input variables, and returns a string containing a MD5 hash. You can see the ...
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1answer
564 views

DCD data in IDA disassmbed file

There is some DCD data in a disassembled binary using IDA as shown the image description. The binary is an ELF of ARM processor type. I want to know what are these data? Is it possible they be code ...
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1answer
481 views

ARM ELF Obfuscation [closed]

Metamorphic is a technique to obfuscate a binary and change the opcode sequence and create new samples with same functionality. In my case, I have some elf binary of ARM processor type and their ...
4
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2answers
830 views

HexRays: Variadic methods like printf

I have identified a routine that behaves exactly like printf in an ARM64 binary. Arguments are passed in the standard fashion (e.g. X0, X1, X2 ...) and I have given the function the signature (Y) of: ...
3
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1answer
162 views

ARMCC/C++ Empty Vtable entries

I am reversing an application for the 3ds which are compiled with ARMCC. I found the vtables of the key classes and have a problem figuring out how the C++ representation of these was. Vtable of ...
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0answers
126 views

Why does IDA mark this as end of function?

I'm analyzing a .so file that is a part of an android application. I've stumbled upon this block of code: LOAD:0001B63C sub_1B63C ; CODE XREF: sub_1B628+Cp LOAD:...
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1answer
403 views

Help with LDRD Instruction

According to documentation, the LDRD instruction works, as follows LDRD R8, R9, [R3, #0x20]; load r8 from a word 32 bytes above the address in R3, and load r9 from a word 36 bytes above the ...
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4answers
1k views

Unpacking xamarin mono dll from libmonodroid_bundle.app.so

I have an apk that was written in xamarin. The meta data suggests there are lots of dlls files this application uses. I found a file called libmonodroid_bundle_app.so which when disassembled in IDA ...
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1answer
1k views

Extract conditional instructions using IDA python in ARM binaries

While using IDA Python for extract ARM instructions, I noticed that some instructions are not extracted completely. For example, conditional instructions such as BCS or BCC are printed as B. For ...
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1answer
290 views

Understanding ARM64 Obj-C Prolog

I'm trying to understand the differences between the following function prologs of a number of obj-c function decompilations. I know they store variables for the caller to use when the function ...
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1answer
780 views

Unable to boot ARM disk image

I'd wish to reverse engineer the firmware of the Netgear R8300 - Nighthawk X8 AC5000 Smart WiFi Router / R8300 (available to download here). I was able to extract the contents of the image using ...
4
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1answer
800 views

ARM “add” instruction with shift

I'm trying to understand how ARM add with shift is implemented e.g. sym.imp.__libc_start_main : ...