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perf, bpf: allow bpf programs attach to tracepoints

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introduce BPF_PROG_TYPE_TRACEPOINT program type and allow it to be attached
to the perf tracepoint handler, which will copy the arguments into
the per-cpu buffer and pass it to the bpf program as its first argument.
The layout of the fields can be discovered by doing
'cat /sys/kernel/debug/tracing/events/sched/sched_switch/format'
prior to the compilation of the program with exception that first 8 bytes
are reserved and not accessible to the program. This area is used to store
the pointer to 'struct pt_regs' which some of the bpf helpers will use:
+---------+
| 8 bytes | hidden 'struct pt_regs *' (inaccessible to bpf program)
+---------+
| N bytes | static tracepoint fields defined in tracepoint/format (bpf readonly)
+---------+
| dynamic | __dynamic_array bytes of tracepoint (inaccessible to bpf yet)
+---------+

Not that all of the fields are already dumped to user space via perf ring buffer
and broken application access it directly without consulting tracepoint/format.
Same rule applies here: static tracepoint fields should only be accessed
in a format defined in tracepoint/format. The order of fields and
field sizes are not an ABI.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov
2016-04-06 18:43:25 -07:00
committed by David S. Miller
parent 1e1dcd93b4
commit 98b5c2c65c
3 changed files with 19 additions and 5 deletions
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10
include/trace/perf.h
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@@ -34,6 +34,7 @@ perf_trace_##call(void *__data, proto) \
struct trace_event_call *event_call = __data; \
struct trace_event_data_offsets_##call __maybe_unused __data_offsets;\
struct trace_event_raw_##call *entry; \
struct bpf_prog *prog = event_call->prog; \
struct pt_regs *__regs; \
u64 __count = 1; \
struct task_struct *__task = NULL; \
@@ -45,7 +46,7 @@ perf_trace_##call(void *__data, proto) \
__data_size = trace_event_get_offsets_##call(&__data_offsets, args); \
\
head = this_cpu_ptr(event_call->perf_events); \
if (__builtin_constant_p(!__task) && !__task && \
if (!prog && __builtin_constant_p(!__task) && !__task && \
hlist_empty(head)) \
return; \
\
@@ -63,6 +64,13 @@ perf_trace_##call(void *__data, proto) \
\
{ assign; } \
\
if (prog) { \
*(struct pt_regs **)entry = __regs; \
if (!trace_call_bpf(prog, entry) || hlist_empty(head)) { \
perf_swevent_put_recursion_context(rctx); \
return; \
} \
} \
perf_trace_buf_submit(entry, __entry_size, rctx, \
event_call->event.type, __count, __regs, \
head, __task); \