Re: [PATCH v3 07/11] perf: Add breakpoint information to siginfo on SIGTRAP
From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-03-24 12:57:02
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linux-fsdevel, linux-kselftest, lkml
On Wed, Mar 24, 2021 at 12:24:59PM +0100, Marco Elver wrote:
quoted hunk ↗ jump to hunk
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.