man/man3/getcwd.3: VERSIONS: The syscall can return "(unreachable)", but modern glibc...

man/man3/getcwd.3: VERSIONS: The syscall can return "(unreachable)", but modern glibc wrapper cannot

I verified using an expirement (see below) that the modern glibc wrapper
getcwd() actually never returns "(unreachable)".  I have also read the
modern glibc sources for all three functions documented here.  None of
them return "(unreachable)".

Now let me describe my expirement:

	d-user@comp:/tmp$ cat getcwd.c
	#include <unistd.h>
	#include <stdio.h>
	#include <sys/syscall.h>

	int
	main(void)
	{
		char  buf[1000];

		if (syscall(SYS_getcwd, buf, sizeof(buf)) == -1)
			perror("SYS_getcwd");
		else
			printf("SYS_getcwd: %s\n", buf);

		if (getcwd(buf, sizeof(buf)) == NULL)
			perror("getcwd");
		else
			printf("getcwd: %s\n", buf);

		return 0;
	}
	d-user@comp:/tmp$ gcc -Wall -Wextra -o getcwd getcwd.c
	d-user@comp:/tmp$ sudo unshare --mount bash
	d-root@comp:/tmp# mkdir /tmp/dir
	d-root@comp:/tmp# mount -t tmpfs tmpfs /tmp/dir
	d-root@comp:/tmp# cd /tmp/dir
	d-root@comp:/tmp/dir# umount -l .
	d-root@comp:/tmp/dir# /tmp/getcwd
	SYS_getcwd: (unreachable)/
	getcwd: No such file or directory
	d-root@comp:/tmp/dir# exit
	exit

Link: <https://sourceware.org/bugzilla/show_bug.cgi?id=18203>
Link: <https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=52a713fdd0a30e1bd79818e2e3c4ab44ddca1a94>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Signed-off-by: Askar Safin <safinaskar@zohomail.com>
Message-ID: <20250220091926.3985504-2-safinaskar@zohomail.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>