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SubjectRe: [RFC] Splitting out kernel<=>userspace ABI headers
On Sep 14, 2005, at 09:46:04, Bill Davidsen wrote:
> H. Peter Anvin wrote:
>> Followup to: <>
>> By author: Erik Andersen <>
>> In newsgroup:
>>> <uClibc maintainer hat on>
>>> That would be wonderful.
>>> </off>
>>> It would be especially nice if everything targeting user space
>>> were to use only all the nice standard ISO C99 types as defined
>>> in include/stdint.h such as uint32_t and friends...
>> Absolutely not. This would be a POSIX namespace violation; they
>> *must* use double-underscore types.
> Could you explain why you think it would be a violation to use
> POSIX types instead of defining our own? That's what the types are
> for, to avoid having everyone define some slightly conflicting types.
> The kernel predates C99, sort of, and it would be a massive but
> valuable task to figure out where a type is really, for instance,
> 32 bits rather than "size of default int" in length, etc, and use
> POSIX types where they are correct. Fewer things to maintain, and
> would make it clear when something is 32 bits by default and when
> it really must be 32 bits.

Argh, it seems I'm going to be giving this example forever! Here's
why this won't work. We want to have sys/stat.h do something like
the following:

# define __kabi_stat64 stat
# include <kabi/stat.h>
/* Now we expect struct stat to be defined with correct types */

Since struct stat in that case uses fixed-bit-size types, the header
fine <kabi/stat.h> needs to include a file providing those types. If
it used stdint.h types, such as uint32_t, then it would need to
#include <stdint.h> or provide the stdint.h types itself. In order
to remain POSIX compliant, sys/stat.h must not include stdint.h or
assume that stdint.h is included or that those types were defined by
the user program. Therefore, kabi/*.h cannot use the stdint.h types
at all! The solution is a separate file, kabi/types.h, which
properly defines __kabi_[su]{8,16,32,64} which are safe to include
and reuse anywhere. Then sys/types.h would look like this:

# include <kabi/types.h>
typedef __kabi_u8 u_int8;
typedef __kabi_s8 int8;
typedef __kabi_u16 u_int16;
typedef __kabi_s16 int16;

Kyle Moffett

Premature optimization is the root of all evil in programming
-- C.A.R. Hoare

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