How to write and execute PURE machine code manuall

Question

I just need a hello world demo to see how machine code actually works.

Though windows' EXE and linux' ELF is near machine code,but it's not PURE

How can I write/execute PURE machine code?

Answer 1

When targeting an embedded system you can make a binary image of the rom or ram that is strictly the instructions and associated data from the program. And often can write that binary into a flash/rom and run it.

Operating systems want to know more than that, and developers often want to leave more than that in their file so they can debug or do other things with it later (disassemble with some recognizable symbol names). Also, embedded or on an operating system you may need to separate .text from .data from .bss from .rodata, etc and file formats like .elf provide a mechanism for that, and the preferred use case is to load that elf with some sort of loader be it the operating system or something programming the rom and ram of a microcontroller.

.exe has some header info as well. As mentioned .com didnt it loaded at address 0x100h and branched there.

to create a raw binary from an executable, with a gcc created elf file for example you can do something like

objcopy file.elf -O binary file.bin

If the program is segmented (.text, .data, etc) and those segments are not back to back the binary can get quite large. Again using embedded as an example if the rom is at 0x00000000 and data or bss is at 0x20000000 even if your program only has 4 bytes of data objcopy will create a 0x20000004 byte file filling in the gap between .text and .data (as it should because that is what you asked it to do).

What is it you are trying to do? Reading a elf or intel hex or srec file are quite trivial and from that you can see all the bits and bytes of the binary. Or disassembling the elf or whatever will also show you that in a human readable form. (objdump -D file.elf > file.list)

Answer 2

On Windows--at least 32bit Windows--you can execute RAW INSTRUCTIONS using a .com file.

For instance, if you take this string and save it in notepad with a .com extension:

X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*

It will print a string and set off your antivirus software.

Answer 3

The next program is an Hello World program I wrote in Machine Code 16 bit (intel 8086), If you want to know machine code, I suggest that you learn Assembly first, because every line of code in Assembly is converted to A code line in Machine Code. For well I know I am from the few people in the world, still programming in Machine Code, instead of Assembly.

BTW, To run it, save the file with a ".com" extension and run on DOSBOX!

So, this is an Hello World Program.