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Date: Thu, 07 Mar 2019 11:03:45 +0100
From: Christian Brauner <christian@...uner.io>
To: Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
CC: Nick Desaulniers <ndesaulniers@...gle.com>,
Oleg Nesterov <oleg@...hat.com>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
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>,
"Gustavo A. R. Silva" <gustavo@...eddedor.com>,
linux-mips@...r.kernel.org
Subject: Re: [PATCH] signal: fix building with clang
On March 7, 2019 10:11:52 AM GMT+01:00, Arnd Bergmann <arnd@...db.de> wrote:
>clang warns about the sigset_t manipulating functions (sigaddset,
>sigdelset,
>sigisemptyset, ...) because it performs semantic analysis before
>discarding
>dead code, unlike gcc that does this in the reverse order.
>
>The result is a long list of warnings like:
>
>In file included from arch/arm64/include/asm/ftrace.h:21:
>include/linux/compat.h:489:10: error: array index 3 is past the end of
>the array (which contains 2 elements) [-Werror,-Warray-bounds]
> case 2: v.sig[3] = (set->sig[1] >> 32); v.sig[2] = set->sig[1];
> ^ ~
>include/linux/compat.h:138:2: note: array 'sig' declared here
> compat_sigset_word sig[_COMPAT_NSIG_WORDS];
> ^
>include/linux/compat.h:489:42: error: array index 2 is past the end of
>the array (which contains 2 elements) [-Werror,-Warray-bounds]
> case 2: v.sig[3] = (set->sig[1] >> 32); v.sig[2] = set->sig[1];
> ^ ~
>include/linux/compat.h:138:2: note: array 'sig' declared here
> compat_sigset_word sig[_COMPAT_NSIG_WORDS];
> ^
>
>As a (rather ugly) workaround, I turn the nice switch()/case statements
>into preprocessor conditionals, and where that is not possible, use the
>'%' operator to modify the warning case into an operation that clang
>will not warn about. Since that only matters for dead code, the actual
>behavior does not change.
>
>Link: https://bugs.llvm.org/show_bug.cgi?id=38789
>Signed-off-by: Arnd Bergmann <arnd@...db.de>
>---
> arch/mips/include/uapi/asm/signal.h | 3 +-
> include/linux/signal.h | 72 ++++++++++++++---------------
> 2 files changed, 37 insertions(+), 38 deletions(-)
>
>diff --git a/arch/mips/include/uapi/asm/signal.h
>b/arch/mips/include/uapi/asm/signal.h
>index 53104b10aae2..8e71a2f778f7 100644
>--- a/arch/mips/include/uapi/asm/signal.h
>+++ b/arch/mips/include/uapi/asm/signal.h
>@@ -11,9 +11,10 @@
> #define _UAPI_ASM_SIGNAL_H
>
> #include <linux/types.h>
>+#include <asm/bitsperlong.h>
>
> #define _NSIG 128
>-#define _NSIG_BPW (sizeof(unsigned long) * 8)
>+#define _NSIG_BPW __BITS_PER_LONG
> #define _NSIG_WORDS (_NSIG / _NSIG_BPW)
>
> typedef struct {
>diff --git a/include/linux/signal.h b/include/linux/signal.h
>index 9702016734b1..b967d502ab61 100644
>--- a/include/linux/signal.h
>+++ b/include/linux/signal.h
>@@ -82,35 +82,33 @@ static inline int sigismember(sigset_t *set, int
>_sig)
>
> static inline int sigisemptyset(sigset_t *set)
> {
>- switch (_NSIG_WORDS) {
>- case 4:
>- return (set->sig[3] | set->sig[2] |
>- set->sig[1] | set->sig[0]) == 0;
>- case 2:
>- return (set->sig[1] | set->sig[0]) == 0;
>- case 1:
>- return set->sig[0] == 0;
>- default:
>- BUILD_BUG();
>- return 0;
>- }
>+#if _NSIG_WORDS == 4
>+ return (set->sig[3] | set->sig[2] |
>+ set->sig[1] | set->sig[0]) == 0;
>+#elif _NSIG_WORDS == 2
>+ return (set->sig[1] | set->sig[0]) == 0;
>+#elif _NSIG_WORDS == 1
>+ return set->sig[0] == 0;
>+#else
>+ BUILD_BUG();
>+#endif
> }
>
>static inline int sigequalsets(const sigset_t *set1, const sigset_t
>*set2)
> {
>- switch (_NSIG_WORDS) {
>- case 4:
>- return (set1->sig[3] == set2->sig[3]) &&
>- (set1->sig[2] == set2->sig[2]) &&
>- (set1->sig[1] == set2->sig[1]) &&
>- (set1->sig[0] == set2->sig[0]);
>- case 2:
>- return (set1->sig[1] == set2->sig[1]) &&
>- (set1->sig[0] == set2->sig[0]);
>- case 1:
>- return set1->sig[0] == set2->sig[0];
>- }
>+#if _NSIG_WORDS == 4
>+ return (set1->sig[3] == set2->sig[3]) &&
>+ (set1->sig[2] == set2->sig[2]) &&
>+ (set1->sig[1] == set2->sig[1]) &&
>+ (set1->sig[0] == set2->sig[0]);
>+#elif _NSIG_WORDS == 2
>+ return (set1->sig[1] == set2->sig[1]) &&
>+ (set1->sig[0] == set2->sig[0]);
>+#elif _NSIG_WORDS == 1
>+ return set1->sig[0] == set2->sig[0];
>+#else
> return 0;
>+#endif
> }
>
> #define sigmask(sig) (1UL << ((sig) - 1))
>@@ -125,14 +123,14 @@ static inline void name(sigset_t *r, const
>sigset_t *a, const sigset_t *b) \
> \
> 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); \
>+ a3 = a->sig[3%_NSIG_WORDS]; a2 = a->sig[2%_NSIG_WORDS]; \
>+ b3 = b->sig[3%_NSIG_WORDS]; b2 = b->sig[2%_NSIG_WORDS]; \
>+ r->sig[3%_NSIG_WORDS] = op(a3, b3); \
>+ r->sig[2%_NSIG_WORDS] = op(a2, b2); \
> /* fall through */ \
> case 2: \
>- a1 = a->sig[1]; b1 = b->sig[1]; \
>- r->sig[1] = op(a1, b1); \
>+ a1 = a->sig[1%_NSIG_WORDS]; b1 = b->sig[1%_NSIG_WORDS]; \
>+ r->sig[1%_NSIG_WORDS] = op(a1, b1); \
> /* fall through */ \
> case 1: \
> a0 = a->sig[0]; b0 = b->sig[0]; \
>@@ -161,10 +159,10 @@ _SIG_SET_BINOP(sigandnsets, _sig_andn)
> static inline void name(sigset_t *set) \
> { \
> switch (_NSIG_WORDS) { \
>- case 4: set->sig[3] = op(set->sig[3]); \
>- set->sig[2] = op(set->sig[2]); \
>+ case 4: set->sig[3%_NSIG_WORDS] = op(set->sig[3%_NSIG_WORDS]); \
>+ set->sig[2%_NSIG_WORDS] = op(set->sig[2%_NSIG_WORDS]); \
> /* fall through */ \
>- case 2: set->sig[1] = op(set->sig[1]); \
>+ case 2: set->sig[1%_NSIG_WORDS] = op(set->sig[1%_NSIG_WORDS]); \
> /* fall through */ \
> case 1: set->sig[0] = op(set->sig[0]); \
> break; \
>@@ -185,7 +183,7 @@ static inline void sigemptyset(sigset_t *set)
> default:
> memset(set, 0, sizeof(sigset_t));
> break;
>- case 2: set->sig[1] = 0;
>+ case 2: set->sig[1%_NSIG_WORDS] = 0;
> /* fall through */
> case 1: set->sig[0] = 0;
> break;
>@@ -198,7 +196,7 @@ static inline void sigfillset(sigset_t *set)
> default:
> memset(set, -1, sizeof(sigset_t));
> break;
>- case 2: set->sig[1] = -1;
>+ case 2: set->sig[1%_NSIG_WORDS] = -1;
> /* fall through */
> case 1: set->sig[0] = -1;
> break;
>@@ -229,7 +227,7 @@ static inline void siginitset(sigset_t *set,
>unsigned long mask)
> default:
> memset(&set->sig[1], 0, sizeof(long)*(_NSIG_WORDS-1));
> break;
>- case 2: set->sig[1] = 0;
>+ case 2: set->sig[1%_NSIG_WORDS] = 0;
> case 1: ;
> }
> }
>@@ -241,7 +239,7 @@ static inline void siginitsetinv(sigset_t *set,
>unsigned long mask)
> default:
> memset(&set->sig[1], -1, sizeof(long)*(_NSIG_WORDS-1));
> break;
>- case 2: set->sig[1] = -1;
>+ case 2: set->sig[1%_NSIG_WORDS] = -1;
> case 1: ;
> }
> }
Ugh, it's not pretty but I don't have any objections. :)
Acked-by: Christian Brauner <christian@...uner.io>
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