If there’s one constant with software developers, it is that sometimes they get bored. At these times, they tend to think dangerous thoughts, usually starting with ‘What if…’. Next you know, they have gone down a dark and winding rabbit hole and found themselves staring at something so amazing that the only natural conclusion that comes to mind is that while educational, it serves no immediate purpose.
The idea of applying this to snipping out the <stdio.h> header in C and the printf() function that it provides definitely is a good example here. Starting from the typical Hello World example in C, [Old Man Yells at Code] over at YouTube first takes us from the standard dynamically linked binary at a bloated 16 kB, to the statically linked version at an eyepopping 767 kB.
To remove any such dynamic linkages, and to keep file sizes somewhat sane, he then proceeds to first use the write()function from the <unistd.h> header, which does indeed cut out the <stdio.h> include, before doing the reasonable thing and removing all includes by rewriting the code in x86 assembly.
While this gets the final binary size down to 9 kB and needs no libraries to link with, it still performs a syscall, after setting appropriate register values, to hand control back to the kernel for doing the actual printing. If you try doing something similar with syscall(), you have to link in libc, so it might very well be that this is the real way to do Hello World without includes or linking in libraries. Plus the asm keyword is part of C, although one could argue that at this point you could just as well write everything in x86 ASM.
Of course, one cannot argue that this experience isn’t incredibly educational, and decidedly answers the original ‘What if…’ question.
Here’s a link to my own software library that includes serial output functions, and a “hello world” program that prints out a heartbeat and echoes typed chars in hex and is 9K bytes long… everything included, including the interrupt table, serial port setup, and ISR for sending characters.
https://hackaday.io/project/177652-arduino-libraries-and-test-programs
I use the code extensively in my projects and for clients, specifically because it’s tiny compared to the STDIO library, it has a tiny memory footprint, and all code is available for verification. (FAA certification does not allow code that will never be called, such as the %p formatting function).
No huge stdio buffer, if you queue up more than 16 characters the system will block until complete. That’s usually not a problem, you usually only use serial output for debugging and it’s more important to use almost no memory than it is to avoid blocking.
At some point in the process the code has to be able to send a single char out the serial port, and that can be either an OS function call, a mapped I/O register that the OS allows access to, or (in the case of arduino) the I/O register itself.
Beyond that, I don’t see how “Hello World” takes up even 16KB.
Heh, or why Balena Etcher is 450 megs… To write images to SD cards. Think of the electricity that this sort of bloat and it’s overhead must be responsible for.
I half expected an asm call, seems like the easy way to do it.
I’m kind of surprised that GCC doesn’t have a built-in function for syscall instruction.
Obligatory older non-video link:
https://www.muppetlabs.com/~breadbox/software/tiny/teensy.html