On Fri, 12 Apr 2024 07:17:09 +0200
Mark Kettenis <mark.kettenis@xs4all.nl> wrote:

> There are all kinds of subtleties with inline functions, but in
> general you'll need to provide a non-inline implementation as well in
> case someone tries to take the address of the function.

htonl(3) is a macro, so I can't take its address.

exam.c:7:18: error: use of undeclared identifier 'htonl'
        printf("%p\n", &htonl);

If I implicitly declare htonl as a function, then I can take its
address.  (Avoid <stdio.h> which pulls in our htonl macro.)

$ cat exam.c
int printf(const char *, ...);
int
main(void)
{
        printf("0x%lx\n", (unsigned long)htonl(0xa1b2c3d4));
        printf("%p\n", &htonl);
}
$ make exam
cc -O2 -pipe    -o exam exam.c 
exam.c:5:35: warning: call to undeclared function 'htonl'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
        printf("0x%lx\n", (unsigned long)htonl(0xa1b2c3d4));
                                         ^
1 warning generated.
$ ./exam
0xa1b2c3d4
0xc0eb59e8

This was with an unmodified libc, because I have not yet applied the
diff.  I believe that macros like htonl don't need functions, but this
diff is correct to keep a function which already exists.