I implemented a function with variable arguments below: Then I hope to implement another named “errExit()” based on the function above. I just tried like below.It works as I hoped but I dont’t think it correct. I tried errExit(“hello,%s,%s,%s”, “arg1″,”arg2̶…
Tag: assembly
Calling libc functions from another shared library in AT&T syntax?
i was trying to assemble codes below to shared library via gcc. i used command below in terminal and got errors. Then i googled the question and got a seemingly feasible answer in undefined-reference-to-main-for-shared-library. Then i added option -no-pie, used commands below and got another error. It seems t…
Removing null bytes for shellcode results in missing char and continuous loop
Update: I have fixed the argv array pointers not being valid causing the continuous loop and have updated the assembly code. Now the only issue is the disappearing space char on compilation. I’ve been experimenting with executing shellcode after exploiting a buffer overflow on a 32-bit Linux VM. My asse…
Use of gs register on a 32 bit program over a 64 bit linux
In a 64 bit program the selector:offset used to get the stack protector is fs:0x28, where fs=0. This poses no problem because in 64 bit we have the MSR fs_base (which is set to point to the TLS) and the GDT is completely ignored. But with 32 bit program the stack protector is read from gs:0x14. Running over a…
How to add 2 numbers together that are of different lengths in x86 linux nasm assembly
I’m very new to assembly and having difficulties in getting basic calculations to work with different length numbers. So this is my adding code, that works with numbers that are 3 or less characters long. for as long as both are the same length. for example 123 + 123 works just fine and outputs 246. But…
How to increase the size of memory region allocated with mmap()
I’m allocating memory using mmap Linux syscall. Is it possible to increase the size of allocated memory region preserving its start address and contents? How to do it properly? Answer On Linux, use the mremap(2) Linux-specific system call without MREMAP_MAYMOVE to extend the existing mapping, without co…
How to print the content of a text file to STDOUT in Linux Assembly Language using c library functions?
First I tried opening a file with fopen function and print content of the file using fprint function but it was just printing a bunch of symbols to the terminal. After a while I realized that it does not take pointer to a stream as argument and above mentioned behaviour was expected. It was printing the actua…
Arduino Uno blink onboard LED by an assembly code gives error Found no label/variable/constant named PD0
I have found an assembly code as follows blink.asm To blink the onboard LED of my Arduino uno (ATmega328P processor). I tried to compile the code to hex by this command But I receive How to fix these errors? My OS is Ubuntu 16.04. Answer This error tell you that the assembler does not know what you mean by PD…
Finding the number of bytes of entered string at runtime
I’m new at learning assembly x86. I have written a program that asks the user to enter a number and then checks if it’s even or odd and then print a message to display this information. The code works fine but it has one problem. It only works for 1 digit numbers: It does not work properly for num…
get a char passed as parameter
I would like to write a function in NASM System V ABI x86-64 (Intel Syntax) that I could use in a C program. Here is the prototype of the function: I therefore retrieve the parameters in order (const char *s = rdi, int c = rsi) First, I get the character stored in the register rsi and put it in