On Thu, 12 Oct 2023 13:45:50 +0200
Artem Savkov <asavkov@xxxxxxxxxx> wrote:
> linux-rt-devel tree contains a patch (b1773eac3f29c ("sched: Add support
> for lazy preemption")) that adds an extra member to struct trace_entry.
> This causes the offset of args field in struct trace_event_raw_sys_enter
> be different from the one in struct syscall_trace_enter:
>
> struct trace_event_raw_sys_enter {
> struct trace_entry ent; /* 0 12 */
>
> /* XXX last struct has 3 bytes of padding */
> /* XXX 4 bytes hole, try to pack */
>
> long int id; /* 16 8 */
> long unsigned int args[6]; /* 24 48 */
> /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
> char __data[]; /* 72 0 */
>
> /* size: 72, cachelines: 2, members: 4 */
> /* sum members: 68, holes: 1, sum holes: 4 */
> /* paddings: 1, sum paddings: 3 */
> /* last cacheline: 8 bytes */
> };
>
> struct syscall_trace_enter {
> struct trace_entry ent; /* 0 12 */
>
> /* XXX last struct has 3 bytes of padding */
>
> int nr; /* 12 4 */
> long unsigned int args[]; /* 16 0 */
>
> /* size: 16, cachelines: 1, members: 3 */
> /* paddings: 1, sum paddings: 3 */
> /* last cacheline: 16 bytes */
> };
>
> This, in turn, causes perf_event_set_bpf_prog() fail while running bpf
> test_profiler testcase because max_ctx_offset is calculated based on the
> former struct, while off on the latter:
>
> 10488 if (is_tracepoint || is_syscall_tp) {
> 10489 int off = trace_event_get_offsets(event->tp_event);
> 10490
> 10491 if (prog->aux->max_ctx_offset > off)
> 10492 return -EACCES;
> 10493 }
>
> What bpf program is actually getting is a pointer to struct
> syscall_tp_t, defined in kernel/trace/trace_syscalls.c. This patch fixes
> the problem by aligning struct syscall_tp_t with with struct
> syscall_trace_(enter|exit) and changing the tests to use these structs
> to dereference context.
>
> Signed-off-by: Artem Savkov <asavkov@xxxxxxxxxx>
Thanks for doing a proper fix.
Acked-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
-- Steve
