From ddecd22878601a606d160680fa85802b75d92eb6 Mon Sep 17 00:00:00 2001 From: Marco Elver <elver@google.com> Date: Mon, 31 Jan 2022 11:34:07 +0100 Subject: perf: uapi: Document perf_event_attr::sig_data truncation on 32 bit architectures Due to the alignment requirements of siginfo_t, as described in 3ddb3fd8cdb0 ("signal, perf: Fix siginfo_t by avoiding u64 on 32-bit architectures"), siginfo_t::si_perf_data is limited to an unsigned long. However, perf_event_attr::sig_data is an u64, to avoid having to deal with compat conversions. Due to being an u64, it may not immediately be clear to users that sig_data is truncated on 32 bit architectures. Add a comment to explicitly point this out, and hopefully help some users save time by not having to deduce themselves what's happening. Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Link: https://lore.kernel.org/r/20220131103407.1971678-3-elver@google.com --- include/uapi/linux/perf_event.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/uapi') diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h index 1b65042ab1db..82858b697c05 100644 --- a/include/uapi/linux/perf_event.h +++ b/include/uapi/linux/perf_event.h @@ -465,6 +465,8 @@ struct perf_event_attr { /* * User provided data if sigtrap=1, passed back to user via * siginfo_t::si_perf_data, e.g. to permit user to identify the event. + * Note, siginfo_t::si_perf_data is long-sized, and sig_data will be + * truncated accordingly on 32 bit architectures. */ __u64 sig_data; }; -- cgit v1.2.3