# kcore
**kcore** is the foundation for the rest of libk. it defines types and structs that are needed by every program, and provides the stub that launches a program's "entry" function. unlike the non-core modules, kcore definitions simply use the prefix `k-`.
## entry
when using libk, your program's entry point will not be the `int main(int,char**)` function that libc opens into. libk will call the function `stat entry(kenv)` instead. like libc, the value returned by `entry` will be returned to the host platform.
## types
kcore contains fixed-width integer types (in <k/type.h>). note that the availability of each depends on your platform; compilation will fail if e.g. you try to use a u64 or a u128 on a 32-bit platform, so where exact lengths are not required, you may wish to use the built-in C types instead.
* `u8` - an unsigned 8-bit integer
* `s8` - a signed 8-bit integer
* `u16` - an unsigned 16-bit integer
* `s16` - a signed 16-bit integer
* `u32` - an unsigned 32-bit integer
* `s32` - a signed 32-bit integer
* `u64` - an unsigned 64-bit integer
* `s64` - a signed 64-bit integer
* `u128` - an unsigned 128-bit integer
* `s128` - a signed 128-bit integer
* `word` - an unsigned integer of platform word-length (e.g. 32 bits on x86.32; 64 on x86.64)
* `sword` - a signed integer of platform word-length (e.g. 32 bits on x86.32; 64 on x86.64)
* `stat` - the type of process return values expected by the platform (usually u8 on linux)
### struct kenv
`kenv` is a struct that encompasses the environment the program was launched in.
* `kiochan std` - a stereo IO channel for reading and writing to and from stdout.
* `kiochan err` - a mono IO channel for writing to stderr.
* `kvar* vars` - a pointer into the program's environment
### struct kvar
`kvar` is a struct that abstracts over platform environment variables.
* `kstr name` - the name of an environment variable
* `kstr val` - the value of an environment variable
* `char* platform` - a pointer into the platform's underlying representation
## functions
### kstop()
`noreturn void kstop(stat)` terminates the program immediately, returning the specified integer to the OS as an exit status. the type of integer it takes depends on your operating system. consider using the `enum kbad` defines in `<k/magic.h>`, which are designed to standardize exit statuses across different software and are synchronized with a FreeBSD effort to do the same (`<sysexit.h`).
## definitions
kcore is the only module that defines any terms outside the k- namespace. the only terms it so defines are native C terms like `noreturn`, which are implemented as keywords in a reserved namespace (`_` followed by an uppercase letter; in this case, `_Noreturn`). macros are then defined in new headers for the "natural" version of the term in order to avoid breaking older code. examples of this technique are `<stdbool.h>` and `<stdnoreturn.h>`. since libk is designed for new, modern code, breaking old code isn't a concern, and we turn on all these new keywords as soon as you load `<k/core.h>`.
libk attempts to find the best possible definition and implementation for these various types and keywords, abstracting across different C versions and dialects. you can go ahead and use the normal version of the keywords (e.g. `noreturn`, `bool`) no matter what kind of compiler you're using and you're guaranteed that as long as you don't go fiddling with undefined- or implementation behavior, your code will behave the same every time. at worst, it may lack a few optimizations or warnings.
(the one minor exception is `null`, a new keyword which libk uses in preference to the ugly, hard-to-type C macro `NULL`.)
`bool` is implemented as a `_Bool` typedef if `_Bool` is available, and as an enum typedef otherwise. either way, and regardless of whether `KFclean` has been defined, booleans can be used and set to the values `true`, `false`, `yes`, or `no`. `yes` and `true` are synonyms, as are `false` and `no`.
### macros
if the flag `KFclean` has not been defined, kcore defines a number of macros to abstract over nonstandard C features. for instance, the `KA*` macros can be used to specify GNU/clang attributes without worrying about compatibility, as they'll automatically be blanked under an incompatible compiler. the KA series includes:
* `KApure` - marks a "pure" function that changes no state and only takes purely numeric arguments, allowing the compiler to avoid repetetive calls to it or even evaluate it at runtime.
* `KAnoreturn` - the GNU/clang-specific version of `noreturn`.
* `KAunused` - acknowledges that a variable is unused and tells the compiler to shut up about it.
* `KAinline` - forces the compiler to inline a function whether it likes it or not.
* `KAflatten` - placed on a function, will force-inline all function calls *made by* that function — sort of like `KAinline` in reverse.
* `KAformat()` - specifies that the function has printf-style syntax for error-checking purposes. worst hack in history.
if you wish to add more (there are like, hundreds) please consider making a merge request. however, the generic macro KA() is also available in the interim: `KA(unused)`.
however, unlike C++ attributes, GNU-style attributes can only be placed on a function declaration, *not* its definition.