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Date:   Tue, 15 Sep 2020 14:25:19 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 2/2] selftests/vm: fix incorrect gcc invocation in some
 cases
Message-ID: <20200915172519.GL1221970@ziepe.ca>
References: <20200915012901.1655280-1-jhubbard@nvidia.com>
 <20200915012901.1655280-3-jhubbard@nvidia.com>
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On Mon, Sep 14, 2020 at 06:29:01PM -0700, John Hubbard wrote:
> Avoid accidental wrong builds, due to built-in rules working just a
> little bit too well--but not quite as well as required for our situation
> here.
> 
> In other words, "make userfaultfd" (for example) is supposed to fail to
> build at all, because this Makefile only supports either "make" (all),
> or "make /full/path". However,  the built-in rules, if not suppressed,
> will pick up CFLAGS and the initial LDLIBS (but not the target-specific
> LDLIBS, because those are only set for the full path target!). This
> causes it to get pretty far into building things despite using incorrect
> values such as an *occasionally* incomplete LDLIBS value.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  tools/testing/selftests/vm/Makefile | 12 ++++++++++++
>  1 file changed, 12 insertions(+)

I hit this too when fiddling with the hmm tests! Would be happy to see
better errors

Jason