Re: linux-next: manual merge of the akpm-current tree with the kspp tree

From: Arnd Bergmann <arnd@arndb.de>
To: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Kees Cook <keescook@google.com>,
	Linux-Next Mailing List <linux-next@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: linux-next: manual merge of the akpm-current tree with the kspp tree
Date: Mon, 15 Jan 2018 13:41:10 +0100	[thread overview]
Message-ID: <CAK8P3a2kjx2x=iC7ei9q36A9TooiZR+d4QTQkfJL6ys7XLtwiQ@mail.gmail.com> (raw)
In-Reply-To: <20180115155710.36e146ab@canb.auug.org.au>

On Mon, Jan 15, 2018 at 5:57 AM, Stephen Rothwell <sfr@canb.auug.org.au> wrote:
> Hi Andrew,
>
> Today's linux-next merge of the akpm-current tree got a conflict in:
>
>   arch/cris/include/arch-v10/arch/bug.h
>
> between commit:
>
>   c8133e59edb0 ("cris: Mark end of BUG() implementation as unreachable")
>
> from the kspp tree and commit:
>
>   c5a1e183a75a ("bug.h: work around GCC PR82365 in BUG()")
>
> from the akpm-current tree.
>
> I fixed it up (I just used the akpm-current tree version) and can
> carry the fix as necessary. This is now fixed as far as linux-next is
> concerned, but any non trivial conflicts should be mentioned to your
> upstream maintainer when your tree is submitted for merging.  You may
> also want to consider cooperating with the maintainer of the conflicting
> tree to minimise any particularly complex conflicts.

Kees,

it seems you ran into the same issue that I did, and got the same fix
for the first BUG() variant, but I think my version for the second one
is slightly better:

 /* This just causes an oops. */
-#define BUG() (*(int *)0 = 0)
+#define BUG()                                                          \
+do {                                                                   \
+       barrier_before_unreachable();                                   \
+       __builtin_trap();                                               \
+} while (0)

compared to yours:

 /* This just causes an oops. */
-#define BUG() (*(int *)0 = 0)
+#define BUG()                                                          \
+do {                                                                   \
+       (*(int *)0 = 0);                                                \
+       do {} while (1);                                                \
+       unreachable();                                                  \
+} while (0)

which relies on a NULL pointer dereference to trap but otherwise
does the same thing. The easiest solution for the conflict seems to
be that you just drop your patch.

       Arnd