[tip:perf/core] tracepoints: Use __u64_aligned/U64_ALIGN()

tip-bot for Mathieu Desnoyers
2011-01-26T07:14:16Z

Commit-ID: 15e3540ce2159705f18fad6147ffedf04445ad64
Gitweb: http://git.kernel.org/tip/15e3540ce2159705f18fad6147ffedf04445ad64
Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
AuthorDate: Fri, 21 Jan 2011 15:36:33 -0500
Committer: Steven Rostedt <rostedt@goodmis.org>
CommitDate: Fri, 21 Jan 2011 22:12:13 -0500

tracepoints: Use __u64_aligned/U64_ALIGN()

commit 7e066fb870fcd1025ec3ba7bbde5d541094f4ce1 added the aligned(32) type and
variable attribute to the tracepoint structures to deal with gcc happily
aligning statically defined structures on 32-byte multiples.

Working on issues within Ftrace, we came up with __64_aligned, which deals with
this issue more elegantly by forcing an 8-byte alignment to both the type
declaration and variable definition.

This therefore saves space, bringing down the size of struct tracepoint from 64
bytes to 38 on 64-bit architectures.

Updating:
- The type attribute (for iteration over the struct tracepoint array)
- Added the variable attribute to the extern definition (needed to force gcc to
consider this alignment for the following definition)
- The definition variable attribute (to force gcc to this specific alignment for
the static definitions)
- The linker script (8-byte alignment can now replace the previous 32-byte
alignment for the custom tracepoint section)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
LKML-Reference: <20110121203643.046218322@efficios.com>
Acked-by: David Miller <davem@davemloft.net>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
include/asm-generic/vmlinux.lds.h | 2 +-
include/linux/tracepoint.h | 12 ++++--------
2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e4af65c..95abb5f 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -176,7 +176,7 @@
CPU_KEEP(exit.data) \
MEM_KEEP(init.data) \
MEM_KEEP(exit.data) \
- . = ALIGN(32); \
+ U64_ALIGN(); \
VMLINUX_SYMBOL(__start___tracepoints) = .; \
*(__tracepoints) \
VMLINUX_SYMBOL(__stop___tracepoints) = .; \
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index c681461..4bc50ea 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -33,12 +33,7 @@ struct tracepoint {
void (*regfunc)(void);
void (*unregfunc)(void);
struct tracepoint_func __rcu *funcs;
-} __attribute__((aligned(32))); /*
- * Aligned on 32 bytes because it is
- * globally visible and gcc happily
- * align these on the structure size.
- * Keep in sync with vmlinux.lds.h.
- */
+} __u64_aligned;

/*
* Connect a probe to a tracepoint.
@@ -146,7 +141,7 @@ static inline void tracepoint_update_probe_range(struct tracepoint *begin,
* structure. Force alignment to the same alignment as the section start.
*/
#define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
- extern struct tracepoint __tracepoint_##name; \
+ extern struct tracepoint __u64_aligned __tracepoint_##name; \
static inline void trace_##name(proto) \
{ \
JUMP_LABEL(&__tracepoint_##name.state, do_trace); \
@@ -178,7 +173,8 @@ do_trace: \
static const char __tpstrtab_##name[] \
__attribute__((section("__tracepoints_strings"))) = #name; \
struct tracepoint __tracepoint_##name \
- __attribute__((section("__tracepoints"), aligned(32))) = \
+ __u64_aligned \
+ __attribute__((section("__tracepoints"))) = \
{ __tpstrtab_##name, 0, reg, unreg, NULL }

#define DEFINE_TRACE(name) \