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authorSteven Rostedt <srostedt@redhat.com>2011-01-27 09:15:30 -0500
committerSteven Rostedt <rostedt@goodmis.org>2011-02-02 21:37:13 -0500
commite4a9ea5ee7c8812a7bf0c3fb725ceeaa3d4c2fcc (patch)
tree1b25668508fa302a6ada053c895cd55727f798f1 /include/trace/ftrace.h
parent9ffdc6c37df131f89d52001e0ef03091b158826f (diff)
tracing: Replace trace_event struct array with pointer array
Currently the trace_event structures are placed in the _ftrace_events section, and at link time, the linker makes one large array of all the trace_event structures. On boot up, this array is read (much like the initcall sections) and the events are processed. The problem is that there is no guarantee that gcc will place complex structures nicely together in an array format. Two structures in the same file may be placed awkwardly, because gcc has no clue that they are suppose to be in an array. A hack was used previous to force the alignment to 4, to pack the structures together. But this caused alignment issues with other architectures (sparc). Instead of packing the structures into an array, the structures' addresses are now put into the _ftrace_event section. As pointers are always the natural alignment, gcc should always pack them tightly together (otherwise initcall, extable, etc would also fail). By having the pointers to the structures in the section, we can still iterate the trace_events without causing unnecessary alignment problems with other architectures, or depending on the current behaviour of gcc that will likely change in the future just to tick us kernel developers off a little more. The _ftrace_event section is also moved into the .init.data section as it is now only needed at boot up. Suggested-by: David Miller <davem@davemloft.net> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: David S. Miller <davem@davemloft.net> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'include/trace/ftrace.h')
-rw-r--r--include/trace/ftrace.h24
1 files changed, 13 insertions, 11 deletions
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index e16610c208c9..3e68366d485a 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -446,14 +446,16 @@ static inline notrace int ftrace_get_offsets_##call( \
* .reg = ftrace_event_reg,
* };
*
- * static struct ftrace_event_call __used
- * __attribute__((__aligned__(4)))
- * __attribute__((section("_ftrace_events"))) event_<call> = {
+ * static struct ftrace_event_call event_<call> = {
* .name = "<call>",
* .class = event_class_<template>,
* .event = &ftrace_event_type_<call>,
* .print_fmt = print_fmt_<call>,
* };
+ * // its only safe to use pointers when doing linker tricks to
+ * // create an array.
+ * static struct ftrace_event_call __used
+ * __attribute__((section("_ftrace_events"))) *__event_<call> = &event_<call>;
*
*/
@@ -579,28 +581,28 @@ static struct ftrace_event_class __used event_class_##call = { \
#undef DEFINE_EVENT
#define DEFINE_EVENT(template, call, proto, args) \
\
-static struct ftrace_event_call __used \
-__attribute__((__aligned__(4))) \
-__attribute__((section("_ftrace_events"))) event_##call = { \
+static struct ftrace_event_call __used event_##call = { \
.name = #call, \
.class = &event_class_##template, \
.event.funcs = &ftrace_event_type_funcs_##template, \
.print_fmt = print_fmt_##template, \
-};
+}; \
+static struct ftrace_event_call __used \
+__attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
#undef DEFINE_EVENT_PRINT
#define DEFINE_EVENT_PRINT(template, call, proto, args, print) \
\
static const char print_fmt_##call[] = print; \
\
-static struct ftrace_event_call __used \
-__attribute__((__aligned__(4))) \
-__attribute__((section("_ftrace_events"))) event_##call = { \
+static struct ftrace_event_call __used event_##call = { \
.name = #call, \
.class = &event_class_##template, \
.event.funcs = &ftrace_event_type_funcs_##call, \
.print_fmt = print_fmt_##call, \
-}
+}; \
+static struct ftrace_event_call __used \
+__attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)

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