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Date: Sun, 16 Mar 1997 19:18:09 +1100
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199703160818.TAA31378@godzilla.zeta.org.au>
To: chuckr@glue.umd.edu, imp@village.org
Subject: Re: Make question
Cc: hackers@freebsd.org
Sender: owner-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

>I think the problem is that /usr/src is a symlink to
>/jaz/FreeBSD/current/src and when I recurse it uses the real path,
>while when I don't it uses $PWD.  When I cd to
>/jaz/FreeBSD/current/src/usr.bin/file rather than
>/usr/src/usr.bin/file, then it picks up the right thing :-(.
>
>Sounds like a bug to me.

Yes, the existence of $PWD support in `make' and shells is probably a bug.
If $PWD is set and has the same device and inode as the real path, then
`make' uses it instead of the path returned by getcwd() for ${.CURDIR}.
It also sets $PWD in the environment to ${.CURDIR} in an attempt to
show a consistent tree to sub-makes.  However, this can't work unless
all shells set $PWD in the same way as `make'.  They don't:

First, the setting of $PWD seen by the top-level make depends on whether
the shell that invoked this make sets and/or exports $PWD.  E.g.,
/bin/sh neither sets nor exports $PWD, but if $PWD is already set and
exported then it will be re-exported (with the wrong value after a cd).
Fix: use only real shells (that don't export $PWD).

Second, sub-makes use /bin/sh, so the behaviour is deterministic, but
it is normal for $PWD to be stale after a cd.  `make' notices that the
device or inode for $PWD is wrong, so it doesn't use the wrong $PWD;
it uses the canonical one instead of the one you want.  This is a
non-problem except for its interaction with the first problem.

Bruce