[PATCH 5.10 515/545] tracing: Use a struct alignof to determine trace event field alignment

Greg Kroah-Hartman
2022-08-19T16:48:56Z

From: Steven Rostedt (Google) <rostedt@goodmis.org>

commit 4c3d2f9388d36eb28640a220a6f908328442d873 upstream.

alignof() gives an alignment of types as they would be as standalone
variables. But alignment in structures might be different, and when
building the fields of events, the alignment must be the actual
alignment otherwise the field offsets may not match what they actually
are.

This caused trace-cmd to crash, as libtraceevent did not check if the
field offset was bigger than the event. The write_msr and read_msr
events on 32 bit had their fields incorrect, because it had a u64 field
between two ints. alignof(u64) would give 8, but the u64 field was at a
4 byte alignment.

Define a macro as:

ALIGN_STRUCTFIELD(type) ((int)(offsetof(struct {char a; type b;}, b)))

which gives the actual alignment of types in a structure.

Link: https://lkml.kernel.org/r/20220731015928.7ab3a154@rorschach.local.home

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 04ae87a52074e ("ftrace: Rework event_create_dir()")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/trace/trace_events.h | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

--- a/include/trace/trace_events.h
+++ b/include/trace/trace_events.h
@@ -400,16 +400,18 @@ static struct trace_event_functions trac

#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)

+#define ALIGN_STRUCTFIELD(type) ((int)(offsetof(struct {char a; type b;}, b)))
+
#undef __field_ext
#define __field_ext(_type, _item, _filter_type) { \
.type = #_type, .name = #_item, \
- .size = sizeof(_type), .align = __alignof__(_type), \
+ .size = sizeof(_type), .align = ALIGN_STRUCTFIELD(_type), \
.is_signed = is_signed_type(_type), .filter_type = _filter_type },

#undef __field_struct_ext
#define __field_struct_ext(_type, _item, _filter_type) { \
.type = #_type, .name = #_item, \
- .size = sizeof(_type), .align = __alignof__(_type), \
+ .size = sizeof(_type), .align = ALIGN_STRUCTFIELD(_type), \
0, .filter_type = _filter_type },

#undef __field
@@ -421,7 +423,7 @@ static struct trace_event_functions trac
#undef __array
#define __array(_type, _item, _len) { \
.type = #_type"["__stringify(_len)"]", .name = #_item, \
- .size = sizeof(_type[_len]), .align = __alignof__(_type), \
+ .size = sizeof(_type[_len]), .align = ALIGN_STRUCTFIELD(_type), \
.is_signed = is_signed_type(_type), .filter_type = FILTER_OTHER },

#undef __dynamic_array