Messages in this thread | | | From | David Laight <> | Subject | RE: [for-next][PATCH 21/21] tracing: Use a struct alignof to determine trace event field alignment | Date | Mon, 1 Aug 2022 07:46:22 +0000 |
| |
From: Steven Rostedt > Sent: 31 July 2022 20:04 > > 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.
The simpler: __alignof__(struct {type b;}) also works.
David
- Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
| |