linux-kernel - Re: [PATCH] signal: fix building with clang

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Date:   Thu, 7 Mar 2019 17:46:48 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-arch <linux-arch@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Christian Brauner <christian@...uner.io>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-mips@...r.kernel.org
Subject: Re: [PATCH] signal: fix building with clang

On 03/07, Arnd Bergmann wrote:
>
> We could use % everywhere,

Yes.

But again, why not simply use the "for (;;)" loops? Why we can't kill the
supid switch(_NSIG_WORDS) tricks altogether?

Oleg.

--- x/include/linux/signal.h
+++ x/include/linux/signal.h
@@ -121,26 +121,9 @@
 #define _SIG_SET_BINOP(name, op)					\
 static inline void name(sigset_t *r, const sigset_t *a, const sigset_t *b) \
 {									\
-	unsigned long a0, a1, a2, a3, b0, b1, b2, b3;			\
-									\
-	switch (_NSIG_WORDS) {						\
-	case 4:								\
-		a3 = a->sig[3]; a2 = a->sig[2];				\
-		b3 = b->sig[3]; b2 = b->sig[2];				\
-		r->sig[3] = op(a3, b3);					\
-		r->sig[2] = op(a2, b2);					\
-		/* fall through */					\
-	case 2:								\
-		a1 = a->sig[1]; b1 = b->sig[1];				\
-		r->sig[1] = op(a1, b1);					\
-		/* fall through */					\
-	case 1:								\
-		a0 = a->sig[0]; b0 = b->sig[0];				\
-		r->sig[0] = op(a0, b0);					\
-		break;							\
-	default:							\
-		BUILD_BUG();						\
-	}								\
+	int i;								\
+	for (i = 0; i < ARRAY_SIZE(r->sig); ++i)			\
+		r->sig[i] = op(a->sig[i], b->sig[i]);			\
 }
 
 #define _sig_or(x,y)	((x) | (y))