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)