[tip:perf/core] bitops: Ensure the compile time HWEIGHT is only used for such

tip-bot for Peter Zijlstra
2010-02-04T09:57:53Z

Commit-ID: fce877e3a429940a986e085a41e8b57f2d922e36
Gitweb: http://git.kernel.org/tip/fce877e3a429940a986e085a41e8b57f2d922e36
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Fri, 29 Jan 2010 13:25:12 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 4 Feb 2010 09:59:50 +0100

bitops: Ensure the compile time HWEIGHT is only used for such

Avoid accidental misuse by failing to compile things

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/cpu/perf_event.c | 10 +++++++---
include/linux/bitops.h | 33 ++++++++++++++++++++++-----------
2 files changed, 29 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 5b91992..96cfc1a 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -93,13 +93,16 @@ struct cpu_hw_events {
struct perf_event *event_list[X86_PMC_IDX_MAX]; /* in enabled order */
};

-#define EVENT_CONSTRAINT(c, n, m) { \
+#define __EVENT_CONSTRAINT(c, n, m, w) {\
{ .idxmsk64[0] = (n) }, \
.code = (c), \
.cmask = (m), \
- .weight = HWEIGHT64((u64)(n)), \
+ .weight = (w), \
}

+#define EVENT_CONSTRAINT(c, n, m) \
+ __EVENT_CONSTRAINT(c, n, m, HWEIGHT(n))
+
#define INTEL_EVENT_CONSTRAINT(c, n) \
EVENT_CONSTRAINT(c, n, INTEL_ARCH_EVTSEL_MASK)

@@ -2622,7 +2625,8 @@ void __init init_hw_perf_events(void)
register_die_notifier(&perf_event_nmi_notifier);

unconstrained = (struct event_constraint)
- EVENT_CONSTRAINT(0, (1ULL << x86_pmu.num_events) - 1, 0);
+ __EVENT_CONSTRAINT(0, (1ULL << x86_pmu.num_events) - 1,
+ 0, x86_pmu.num_events);

pr_info("... version: %d\n", x86_pmu.version);
pr_info("... bit width: %d\n", x86_pmu.event_bits);
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index ba0fd1e..25b8b2f 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -45,19 +45,30 @@ static inline unsigned long hweight_long(unsigned long w)
return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
}

-#define HWEIGHT8(w) \
- ( (!!((w) & (1ULL << 0))) + \
- (!!((w) & (1ULL << 1))) + \
- (!!((w) & (1ULL << 2))) + \
- (!!((w) & (1ULL << 3))) + \
- (!!((w) & (1ULL << 4))) + \
- (!!((w) & (1ULL << 5))) + \
- (!!((w) & (1ULL << 6))) + \
+/*
+ * Clearly slow versions of the hweightN() functions, their benefit is
+ * of course compile time evaluation of constant arguments.
+ */
+#define HWEIGHT8(w) \
+ ( BUILD_BUG_ON_ZERO(!__builtin_constant_p(w)) + \
+ (!!((w) & (1ULL << 0))) + \
+ (!!((w) & (1ULL << 1))) + \
+ (!!((w) & (1ULL << 2))) + \
+ (!!((w) & (1ULL << 3))) + \
+ (!!((w) & (1ULL << 4))) + \
+ (!!((w) & (1ULL << 5))) + \
+ (!!((w) & (1ULL << 6))) + \
(!!((w) & (1ULL << 7))) )

-#define HWEIGHT16(w) (HWEIGHT8(w) + HWEIGHT8(w >> 8))
-#define HWEIGHT32(w) (HWEIGHT16(w) + HWEIGHT16(w >> 16))
-#define HWEIGHT64(w) (HWEIGHT32(w) + HWEIGHT32(w >> 32))
+#define HWEIGHT16(w) (HWEIGHT8(w) + HWEIGHT8((w) >> 8))
+#define HWEIGHT32(w) (HWEIGHT16(w) + HWEIGHT16((w) >> 16))
+#define HWEIGHT64(w) (HWEIGHT32(w) + HWEIGHT32((w) >> 32))
+
+/*
+ * Type invariant version that simply casts things to the
+ * largest type.
+ */
+#define HWEIGHT(w) HWEIGHT64((u64)(w))

/**
* rol32 - rotate a 32-bit value left