Re: [RFC][PATCH 1/2] Create initial kernel ABI header infrastructure

From: Kyle Moffett
Date: Sat Apr 01 2006 - 21:59:49 EST


On Apr 1, 2006, at 19:22:13, Randy.Dunlap wrote:
On Wed, 29 Mar 2006 22:26:41 +0000 Pavel Machek wrote:
I plan to add a lot of other definitions to this file later on. For example different architectures have
different notions of what a __kernel_ino_t is (unsigned int versus unsigned long). I may rename this file as types.h, but from looking through the code I figure I'll have enough general purpose declarations about "This architecture has blah" that a separate stddef.h file will be worth it.

(and... why do you prefix these with _KABI? that's a mistake imo. Don't bother with that. Really. Either these need exporting to userspace, but then either use __ as prefix or don't use a prefix. But KABI.. No.)

According to the various standards all symbols beginning with __ are reserved for "The Implementation", including the compiler, the standard library, the kernel, etc. In order to avoid clashing with any/all of those, I picked the __KABI_ and __kabi_ prefixes for uniqueness. In theory I could just use __, but there are problems with that too. For example, note how the current compiler.h files redefine __always_inline to mean something kinda different. The GCC manual says we should be able to write this:

__KABI_ everywhere will just make your headers totally unreadable. Please don't do that.

Ack, I agree.

Let me reiterate two facts:

(1) The various C standards state that the implementation should restrict itself to symbols prefixed with "__", everything else is reserved for user code (Including symbols prefixed with a single underscore).
(2) GCC predefines a large collection of symbols, macros, and functions for its own use, and this set is not constant (just look at the number of new __-prefixed symbols added between GCC 3 and 4. In addition, we're not just compiling this code under GCC, but people will also be using it (hopefully unmodified) under tiny-cc, intel-cc, PGI, PathScale, Lahey, ARM Ltd, lcc, and possibly others. It probably does not need to be stated that for something as userspace- sensitive as the KABI headers we should not risk colliding with predefined builtins in any of those compilers.

So my question to the list is this:
Can you come up with any way other than using a "__kabi_" prefix to reasonably avoid namespace collisions with that large list of compilers? If you have some way, I'd be interested to hear it, but as a number of those compilers are commercial I'd have no way to test on them (and I suspect most people on this list would not either).

Of course, if the general consensus is that supporting non-GCC is not important, then that's ok with me. Judging from the number of negative responses my earlier "[OT] Non-GCC compilers used for linux userspace" got, however, that doesn't seem to be the case.

Thanks for the advice!

Cheers,
Kyle Moffett

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