You can if you're super duper careful and throw in a little inline asm, depending on the architecture. ARM for instance is very likely not to need to spill to the stack on tiny little leaf functions.

It's an absolutely terrible idea, but I've seen engineers be so afraid of asm files that they'd try something like this.

The ARM Cortex-M series of chips is I believe kind enough to initialize the stack pointer for you before your code even executes, by copying your chosen stack pointer value from a special reserved location in the interrupt vector table. So in principle you could write all your hardware init code in C.

Yes, exactly this. As someone who has written startup code in many flavors of assembly (PIC, ARMv4, MIPS, PowerPC, AVR...), I appreciated what ARM did with the design of the Cortex-M architecture -- they designed it so that you could write fully-functional embedded software (firmware) without a line of assembly.

Normally, the 2 places you can't avoid assembly are (1) the startup code (because you're doing things like disabling interrrupts and setting the stack pointer) and (2) interrupt service routines - usually there is a little bit of magic on the front and back ends (for example on an older ARM7 chip, the CPU didn't automatically push / save any registers onto the stack, you had to do it yourself if you needed that).

With the Cortex-M, the CPU design and its microcode took care of all that, so all of the messy assembly stuff went away. Now, as someone who started writing 6502 ASM as a kid, I kind of miss it, but as someone who has to build lots of systems and ship products on deadlines, I like the change.

Eh, on the M4s, they borked it. There's an errata that the floating point spill doesn't take into account the divide pipeline, so it can not wait enough time for the pipeline flush, and corrupt the register save. So you have to write your own asm interrupt prologue anyway. : /