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.
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| @@ -465,6 +465,8 @@ struct perf_event_attr { · 464 unmodified lines | |||
| 465 | /* | 465 | /* |
| 466 | * User provided data if sigtrap=1, passed back to user via | 466 | * User provided data if sigtrap=1, passed back to user via |
| 467 | * siginfo_t::si_perf_data, e.g. to permit user to identify the event. | 467 | * siginfo_t::si_perf_data, e.g. to permit user to identify the event. |
| 468 | * Note, siginfo_t::si_perf_data is long-sized, and sig_data will be | ||
| 469 | * truncated accordingly on 32 bit architectures. | ||
| 468 | */ | 470 | */ |
| 469 | __u64 sig_data; | 471 | __u64 sig_data; |
| 470 | }; | 472 | }; |