On 18/02/15 19:21, Jeff Prothero wrote: > BTW, I'd also be curious to know what is regarded as engineering > best practice for writing a value to address zero when this is > architecturally required by the hardware platform at hand. > Obviously one can do various things to obscure the process > sufficiently that the current gcc implementation won't detect it and > complain, but as gcc gets smarter about optimization those are at > risk of failing in a future release. It would be nice to have a > guaranteed-to-work future-proof idiom for doing this. Do we have > one, short of retreating to assembly code?
I doubt that such a thing is ever going to be safe. The idea that a null pointer points to nothing is so hard-baked into the design of C that you can't get away from it. Also, almost every C programmer and especially library writer "knows" that a null pointer points to nothing. The only way to initialize an interrupt vector table at address zero is to go outside the language. While it may be possible to use some proprietary GCC options to get around this, it's never going to be a good idea because some GCC author (or indeed library author) may make the "mistake" of assuming that null pointer point to nothing. Using C to initialize anything at address zero is so dangerous that we shouldn't tell people that they can use such-and-such a GCC option to support it; we should warn them never to do it, and provide as many warnings as we can. IMO, engineering best practice is to use assembly code. Andrew.
