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Subject[PATCH 06/12] perf: Return empty callchain instead of NULL
Date
It simplifies the code a bit, because we dump the callchain
even if it's empty. With 'empty' callchain we can remove
all the NULL-checking code paths.

Original-patch-from: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-n4t869o2qc1b31v4wwvmxznb@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
kernel/events/core.c | 30 ++++++++++++------------------
1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5fc1ded4b450..4e1a1bf8d867 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5815,19 +5815,11 @@ void perf_output_sample(struct perf_output_handle *handle,
perf_output_read(handle, event);

if (sample_type & PERF_SAMPLE_CALLCHAIN) {
- if (data->callchain) {
- int size = 1;
-
- if (data->callchain)
- size += data->callchain->nr;
-
- size *= sizeof(u64);
+ int size = 1;

- __output_copy(handle, data->callchain, size);
- } else {
- u64 nr = 0;
- perf_output_put(handle, nr);
- }
+ size += data->callchain->nr;
+ size *= sizeof(u64);
+ __output_copy(handle, data->callchain, size);
}

if (sample_type & PERF_SAMPLE_RAW) {
@@ -5980,6 +5972,8 @@ static u64 perf_virt_to_phys(u64 virt)
return phys_addr;
}

+static struct perf_callchain_entry __empty_callchain = { .nr = 0, };
+
static struct perf_callchain_entry *
perf_callchain(struct perf_event *event, struct pt_regs *regs)
{
@@ -5988,12 +5982,14 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
/* Disallow cross-task user callchains. */
bool crosstask = event->ctx->task && event->ctx->task != current;
const u32 max_stack = event->attr.sample_max_stack;
+ struct perf_callchain_entry *callchain;

if (!kernel && !user)
- return NULL;
+ return &__empty_callchain;

- return get_perf_callchain(regs, 0, kernel, user,
- max_stack, crosstask, true);
+ callchain = get_perf_callchain(regs, 0, kernel, user,
+ max_stack, crosstask, true);
+ return callchain ?: &__empty_callchain;
}

void perf_prepare_sample(struct perf_event_header *header,
@@ -6018,9 +6014,7 @@ void perf_prepare_sample(struct perf_event_header *header,
int size = 1;

data->callchain = perf_callchain(event, regs);
-
- if (data->callchain)
- size += data->callchain->nr;
+ size += data->callchain->nr;

header->size += size * sizeof(u64);
}
--
2.13.6
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