Re: What are __dead2 and __unused in the source code?

On Tue, 21 Nov 2023 15:12:51 +0100
Mehdi Khawari <iam.mehdikhawari@gmail.com> wrote:

> Hi, everyone!
> 
> I'm just learning by studying the source code of some basic tools
> included in the base and I had a question.

	These macros are defined in /usr/include/sys/cdefs.h, they're
hints to the compiler to prevent warnings that would otherwise occur and
break the build with --Wall which turns all warnings into errors.

> Why is __dead2 applied to some function like usage?
> static void usage(void) __dead2;

	__dead2 hints that the function is not expected to return.

> What is the reason that __unused is applied to the function argument like
> here:

	__unused lets the compiler know that this parameter is not used
intentionally.

> static void
> siginfo_handler(int sig __unused)
> {
> siginfo = 1;
> }
> These snippets are from /bin/chmod/chmod.c. Where can I find more
> information on this?

	In each case without the hint the compiler would throw a warning,
which the default --Wall option would turn into an error.

	There's a NetBSD manpage which covers similar constructs, but there
doesn't seem to be a FreeBSD version of it.

https://man.netbsd.org/NetBSD-6.1/__dead.3

-- 
Steve O'Hara-Smith <steve@sohara.org>