Yes, embedded is very side-effect-ful. When you have to make that kind of thing work, you usually have to know both your hardware architecture and your compiler.
*(unsigned long*)0xEF010014 = 0x1C;
presumes memory mapped I/O, a 32-bit hardware register at 0xEF010014, and what 0x1C will mean to that register. It also presumes that the compiler will generate a 32-bit access for an unsigned long.
Going back to Gibbon1's code sample, you have to know what your compiler is going to do at what optimization level. You either have to declare spi.S to be volatile, or you have to compile at -O0, or some such. And you may well need to review the generated assembly code a few times in order to really understand what your compiler is doing with your code.
If you're writing the Linux kernel and you want to be portable across hardware architectures, it gets harder. You can't just be processor- or hardware-specific. You probably need the volatile keyword. I don't know what the kernel compiles in terms of optimizations, but I bet it's not aggressively optimized.
Going back to Gibbon1's code sample, you have to know what your compiler is going to do at what optimization level. You either have to declare spi.S to be volatile, or you have to compile at -O0, or some such. And you may well need to review the generated assembly code a few times in order to really understand what your compiler is doing with your code.
If you're writing the Linux kernel and you want to be portable across hardware architectures, it gets harder. You can't just be processor- or hardware-specific. You probably need the volatile keyword. I don't know what the kernel compiles in terms of optimizations, but I bet it's not aggressively optimized.