NOTE(3EXT) Extended Library Functions NOTE(3EXT)

NAME

NOTE, _NOTE - annotate source code with info for tools

SYNOPSIS

#include <note.h>


NOTE(NoteInfo);


or
#include <sys/note.h>


_NOTE(NoteInfo);

DESCRIPTION

These macros are used to embed information for tools in program
source. A use of one of these macros is called an "annotation". A
tool may define a set of such annotations which can then be used to
provide the tool with information that would otherwise be unavailable
from the source code.


Annotations should, in general, provide documentation useful to the
human reader. If information is of no use to a human trying to
understand the code but is necessary for proper operation of a tool,
use another mechanism for conveying that information to the tool (one
which does not involve adding to the source code), so as not to
detract from the readability of the source. The following is an
example of an annotation which provides information of use to a tool
and to the human reader (in this case, which data are protected by a
particular lock, an annotation defined by the static lock analysis
tool lock_lint).

NOTE(MUTEX_PROTECTS_DATA(foo_lock, foo_list Foo))


Such annotations do not represent executable code; they are neither
statements nor declarations. They should not be followed by a
semicolon. If a compiler or tool that analyzes C source does not
understand this annotation scheme, then the tool will ignore the
annotations. (For such tools, NOTE(x) expands to nothing.)


Annotations may only be placed at particular places in the source.
These places are where the following C constructs would be allowed:

o a top-level declaration (that is, a declaration not within
a function or other construct)

o a declaration or statement within a block (including the
block which defines a function)

o a member of a struct or union.


Annotations are not allowed in any other place. For example, the
following are illegal:

x = y + NOTE(...) z ;
typedef NOTE(...) unsigned int uint ;


While NOTE and _NOTE may be used in the places described above, a
particular type of annotation may only be allowed in a subset of
those places. For example, a particular annotation may not be
allowed inside a struct or union definition.

NOTE vs _NOTE
Ordinarily, NOTE should be used rather than _NOTE, since use of _NOTE
technically makes a program non-portable. However, it may be
inconvenient to use NOTE for this purpose in existing code if NOTE is
already heavily used for another purpose. In this case one should
use a different macro and write a header file similar to
/usr/include/note.h which maps that macro to _NOTE in the same
manner. For example, the following makes FOO such a macro:

#ifndef _FOO_H
#define _FOO_H
#define FOO _NOTE
#include <sys/note.h>
#endif


Public header files which span projects should use _NOTE rather than
NOTE, since NOTE may already be used by a program which needs to
include such a header file.

NoteInfo Argument
The actual NoteInfo used in an annotation should be specified by a
tool that deals with program source (see the documentation for the
tool to determine which annotations, if any, it understands).


NoteInfo must have one of the following forms:

NoteName
NoteName(Args)


where NoteName is simply an identifier which indicates the type of
annotation, and Args is something defined by the tool that specifies
the particular NoteName. The general restrictions on Args are that it
be compatible with an ANSI C tokenizer and that unquoted parentheses
be balanced (so that the end of the annotation can be determined
without intimate knowledge of any particular annotation).

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|MT-Level | Safe |
+---------------+-----------------+

SEE ALSO

note(5), attributes(7)

June 18, 2021 NOTE(3EXT)