On Wed, Mar 24, 2021 at 01:53:48PM +0100, Peter Zijlstra wrote:
On Wed, Mar 24, 2021 at 12:24:59PM +0100, Marco Elver wrote:
Encode information from breakpoint attributes into siginfo_t, which helps disambiguate which breakpoint fired.
Note, providing the event fd may be unreliable, since the event may have been modified (via PERF_EVENT_IOC_MODIFY_ATTRIBUTES) between the event triggering and the signal being delivered to user space.
Signed-off-by: Marco Elver elver@google.com
v2:
- Add comment about si_perf==0.
kernel/events/core.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 1e4c949bf75f..0316d39e8c8f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6399,6 +6399,22 @@ static void perf_sigtrap(struct perf_event *event) info.si_signo = SIGTRAP; info.si_code = TRAP_PERF; info.si_errno = event->attr.type;
- switch (event->attr.type) {
- case PERF_TYPE_BREAKPOINT:
info.si_addr = (void *)(unsigned long)event->attr.bp_addr;info.si_perf = (event->attr.bp_len << 16) | (u64)event->attr.bp_type;Ahh, here's the si_perf user. I wasn't really clear to me what was supposed to be in that field at patch #5 where it was introduced.
Would it perhaps make sense to put the user address of struct perf_event_attr in there instead? (Obviously we'd have to carry it from the syscall to here, but it might be more useful than a random encoding of some bits therefrom).
Then we can also clearly document that's in that field, and it might be more useful for possible other uses.
Something like so...
---
--- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -778,6 +778,8 @@ struct perf_event { void *security; #endif struct list_head sb_list; + + struct perf_event_attr __user *uattr; #endif /* CONFIG_PERF_EVENTS */ };
--- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5652,13 +5652,17 @@ static long _perf_ioctl(struct perf_even return perf_event_query_prog_array(event, (void __user *)arg);
case PERF_EVENT_IOC_MODIFY_ATTRIBUTES: { + struct perf_event_attr __user *uattr; struct perf_event_attr new_attr; - int err = perf_copy_attr((struct perf_event_attr __user *)arg, - &new_attr); + int err;
+ uattr = (struct perf_event_attr __user *)arg; + err = perf_copy_attr(uattr, &new_attr); if (err) return err;
+ event->uattr = uattr; + return perf_event_modify_attr(event, &new_attr); } default: @@ -6400,6 +6404,8 @@ static void perf_sigtrap(struct perf_eve info.si_signo = SIGTRAP; info.si_code = TRAP_PERF; info.si_errno = event->attr.type; + info.si_perf = (unsigned long)event->uattr; + force_sig_info(&info); }
@@ -12011,6 +12017,8 @@ SYSCALL_DEFINE5(perf_event_open, goto err_task; }
+ event->uattr = attr_uptr; + if (is_sampling_event(event)) { if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) { err = -EOPNOTSUPP;