From: Greg KH on
2.6.32-stable review patch. If anyone has any objections, please let us know.


From: Jeff Mahoney <jeffm(a)>

commit 86c38a31aa7f2dd6e74a262710bf8ebf7455acc5 upstream.

GCC 4.5 introduces behavior that forces the alignment of structures to
use the largest possible value. The default value is 32 bytes, so if
some structures are defined with a 4-byte alignment and others aren't
declared with an alignment constraint at all - it will align at 32-bytes.

For things like the ftrace events, this results in a non-standard array.
When initializing the ftrace subsystem, we traverse the _ftrace_events
section and call the initialization callback for each event. When the
structures are misaligned, we could be treating another part of the
structure (or the zeroed out space between them) as a function pointer.

This patch forces the alignment for all the ftrace_event_call structures
to 4 bytes.

Without this patch, the kernel fails to boot very early when built with
gcc 4.5.

It's trivial to check the alignment of the members of the array, so it
might be worthwhile to add something to the build system to do that
automatically. Unfortunately, that only covers this case. I've asked one
of the gcc developers about adding a warning when this condition is seen.

Cc: stable(a)
Signed-off-by: Jeff Mahoney <jeffm(a)>
LKML-Reference: <4B85770B.6010901(a)>
Signed-off-by: Steven Rostedt <rostedt(a)>
Cc: Andreas Radke <a.radke(a)>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)>

include/linux/syscalls.h | 6 ++++--
include/trace/ftrace.h | 3 ++-
kernel/trace/trace.h | 3 ++-
3 files changed, 8 insertions(+), 4 deletions(-)

--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -153,7 +153,8 @@ static void prof_sysexit_disable_##sname
#define __SC_STR_TDECL6(t, a, ...) #t, __SC_STR_TDECL5(__VA_ARGS__)

- static struct ftrace_event_call event_enter_##sname; \
+ static struct ftrace_event_call \
+ __attribute__((__aligned__(4))) event_enter_##sname; \
struct trace_event enter_syscall_print_##sname = { \
.trace = print_syscall_enter, \
}; \
@@ -189,7 +190,8 @@ static void prof_sysexit_disable_##sname

- static struct ftrace_event_call event_exit_##sname; \
+ static struct ftrace_event_call \
+ __attribute__((__aligned__(4))) event_exit_##sname; \
struct trace_event exit_syscall_print_##sname = { \
.trace = print_syscall_exit, \
}; \
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -43,7 +43,8 @@
tstruct \
char __data[0]; \
}; \
- static struct ftrace_event_call event_##name
+ static struct ftrace_event_call \
+ __attribute__((__aligned__(4))) event_##name

#undef __cpparg
#define __cpparg(arg...) arg
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -746,7 +746,8 @@ extern const char *__stop___trace_bprint

#define FTRACE_ENTRY(call, struct_name, id, tstruct, print) \
- extern struct ftrace_event_call event_##call;
+ extern struct ftrace_event_call \
+ __attribute__((__aligned__(4))) event_##call;
#define FTRACE_ENTRY_DUP(call, struct_name, id, tstruct, print) \
FTRACE_ENTRY(call, struct_name, id, PARAMS(tstruct), PARAMS(print))

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