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@xxxxxxxxxxxx>
CC: David Miller <davem@xxxxxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxx>
---
include/asm-generic/vmlinux.lds.h | 2 +-
include/linux/tracepoint.h | 12 ++++--------
2 files changed, 5 insertions(+), 9 deletions(-)
Index: linux-2.6-lttng/include/asm-generic/vmlinux.lds.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-generic/vmlinux.lds.h
+++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h
@@ -168,7 +168,7 @@
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) = .; \
Index: linux-2.6-lttng/include/linux/tracepoint.h
===================================================================
--- linux-2.6-lttng.orig/include/linux/tracepoint.h
+++ linux-2.6-lttng/include/linux/tracepoint.h
@@ -33,12 +33,7 @@ struct tracepoint {
void (*regfunc)(void);
void (*unregfunc)(void);
struct tracepoint_func *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.
@@ -143,7 +138,7 @@ static inline void tracepoint_update_pro
* structure. Force alignment to the same alignment as the section start.
*/
#define __DECLARE_TRACE(name, proto, args, 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); \
@@ -174,7 +169,8 @@ 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) \
--
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