Startup and Configuration

Configuration data and startup code for the kernel.

void kernel_init(void)

Initializes scheduler and creates main and idle task.

container_of( PTR, TYPE, MEMBER)

Returns the container of a pointer to a member. 

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((TYPE *) ((char *) (PTR) - offsetof(TYPE, MEMBER)))

For a struct TYPE with a member MEMBER, given a pointer PTR to TYPE::MEMBER this function returns a pointer to the instance of TYPE.

E.g. for struct my_struct_t { ...; something_t n; ... } my_struct;, &my_struct == container_of(&my_struct.n, struct my_struct_t, n).

Parameters

PTR:pointer to a member
TYPE:a type name (a struct or union), container of PTR
MEMBER:name of the member of TYPE which PTR points to

Return values

  • Pointer to the container of PTR.
NORETURN

The NORETURN keyword tells the compiler to assume that the function cannot return.

CONST

A function declared as CONST is kernel_defines.h::PURE and also not allowed to examine global memory.

I.e. a CONST function cannot even dereference a pointer parameter.

PURE

The function has no effects except the return value and its return value depends only on the parameters and/or global variables.

Such a function can be subject to common subexpression elimination and loop optimization just as an arithmetic operator would be.

UNREACHABLE()

Tell the compiler that this line of code cannot be reached. 

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do { /* nothing */ } while (1)

Most useful in junction with kernel_defines.h::NORETURN. Use this if the compiler cannot tell that e.g. an assembler instruction causes a longjmp, or a write causes a reboot.

ALIGN_OF( T)

Calculate the minimal alignment for type T. 

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(offsetof(struct { char c; T t; }, t))

Parameters

T:Type to examine

Return values

  • The minimal alignment of T.
BUILD_BUG_ON( condition)

Forces a compilation error if condition is true. 

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((void)sizeof(char[1 - 2 * !!(condition)]))

This trick is only needed if the condition can’t be evaluated before compile time (i.e. sizeof(sometype_t) < 42 ) For more details on this see for example: https://git.kernel.org/pub/scm/linux/kernel/git/stable/ linux-stable.git/tree/include/linux/bug.h

Parameters

condition:A condition that will be evaluated at compile time