Messages in this thread | | | From | Kyle Moffett <> | Subject | Re: [RFC][PATCH 1/2] Create initial kernel ABI header infrastructure | Date | Sat, 1 Apr 2006 21:42:14 -0500 |
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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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