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Subject[PATCH 4/6] perf record: Handle argument change in sched_switch
Date
Recently sched_switch tracepoint added a new argument for prev_state,
but it's hard to handle the change in a BPF program. Instead, we can
check the function prototype in BTF before loading the program.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/bpf_off_cpu.c | 28 +++++++++++++++++++++
tools/perf/util/bpf_skel/off_cpu.bpf.c | 35 ++++++++++++++++++--------
2 files changed, 52 insertions(+), 11 deletions(-)

diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
index b5e2d038da50..874856c55101 100644
--- a/tools/perf/util/bpf_off_cpu.c
+++ b/tools/perf/util/bpf_off_cpu.c
@@ -89,6 +89,33 @@ static void off_cpu_finish(void *arg __maybe_unused)
off_cpu_bpf__destroy(skel);
}

+/* v5.18 kernel added prev_state arg, so it needs to check the signature */
+static void check_sched_switch_args(void)
+{
+ const struct btf *btf = bpf_object__btf(skel->obj);
+ const struct btf_type *t1, *t2, *t3;
+ u32 type_id;
+
+ type_id = btf__find_by_name_kind(btf, "bpf_trace_sched_switch",
+ BTF_KIND_TYPEDEF);
+ if ((s32)type_id < 0)
+ return;
+
+ t1 = btf__type_by_id(btf, type_id);
+ if (t1 == NULL)
+ return;
+
+ t2 = btf__type_by_id(btf, t1->type);
+ if (t2 == NULL || !btf_is_ptr(t2))
+ return;
+
+ t3 = btf__type_by_id(btf, t2->type);
+ if (t3 && btf_is_func_proto(t3) && btf_vlen(t3) == 4) {
+ /* new format: pass prev_state as 4th arg */
+ skel->rodata->has_prev_state = true;
+ }
+}
+
int off_cpu_prepare(struct evlist *evlist, struct target *target)
{
int err, fd, i;
@@ -117,6 +144,7 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target)
}

set_max_rlimit();
+ check_sched_switch_args();

err = off_cpu_bpf__load(skel);
if (err) {
diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
index 78cdcc8ff863..986d7db6e75d 100644
--- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
+++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
@@ -72,6 +72,8 @@ int enabled = 0;
int has_cpu = 0;
int has_task = 0;

+const volatile bool has_prev_state = false;
+
/*
* Old kernel used to call it task_struct->state and now it's '__state'.
* Use BPF CO-RE "ignored suffix rule" to deal with it like below:
@@ -121,22 +123,13 @@ static inline int can_record(struct task_struct *t, int state)
return 1;
}

-SEC("tp_btf/sched_switch")
-int on_switch(u64 *ctx)
+static int off_cpu_stat(u64 *ctx, struct task_struct *prev,
+ struct task_struct *next, int state)
{
__u64 ts;
- int state;
__u32 stack_id;
- struct task_struct *prev, *next;
struct tstamp_data *pelem;

- if (!enabled)
- return 0;
-
- prev = (struct task_struct *)ctx[1];
- next = (struct task_struct *)ctx[2];
- state = get_task_state(prev);
-
ts = bpf_ktime_get_ns();

if (!can_record(prev, state))
@@ -180,4 +173,24 @@ int on_switch(u64 *ctx)
return 0;
}

+SEC("tp_btf/sched_switch")
+int on_switch(u64 *ctx)
+{
+ struct task_struct *prev, *next;
+ int prev_state;
+
+ if (!enabled)
+ return 0;
+
+ prev = (struct task_struct *)ctx[1];
+ next = (struct task_struct *)ctx[2];
+
+ if (has_prev_state)
+ prev_state = (int)ctx[3];
+ else
+ prev_state = get_task_state(prev);
+
+ return off_cpu_stat(ctx, prev, next, prev_state);
+}
+
char LICENSE[] SEC("license") = "Dual BSD/GPL";
--
2.36.1.124.g0e6072fb45-goog
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