Radare2

Play with empty buffers

Run radare2 with empty buffer

If you want to try doing some shellcode sheningans without needing to load a full file you can use the r2 empty buffer

r2 -
r2  malloc://${bufferSizeInBytes} 
# r2 malloc://512

Write in the empty buffer

Once r2 has been run and the buffer initialized, you can use w to write a binary shellcode from a file into the allocated buffer or use wx to write an hexa shellcode into the allocated buffer

wx 554889e548c705....

Emulate the ASM written in the buffer

# Initialize the VM
aei 
# Initialize the stack
aeim
# Initialize the program counter

The go in visual mode with V and go to the ASM and registry view with P and type F7 to step into or F8 to step over the instruction

Visual mode

You can type V to enter the visual mode. Type P to change the view.