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

[Kyle Moffett]

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