1// Copyright (c) 2020-present The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#ifndef BITCOIN_UTIL_TRACE_H
6#define BITCOIN_UTIL_TRACE_H
7
8#include <bitcoin-build-config.h> // IWYU pragma: keep
9
10#ifdef ENABLE_TRACING
11
12// Workaround for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103395
13// systemtap 4.6 on 32-bit ARM triggers internal compiler error
14// (this workaround is included in systemtap 4.7+)
15#if defined(__arm__)
16#  define STAP_SDT_ARG_CONSTRAINT g
17#endif
18
19// Setting SDT_USE_VARIADIC lets systemtap (sys/sdt.h) know that we want to use
20// the optional variadic macros to define tracepoints.
21#define SDT_USE_VARIADIC 1
22
23// Setting _SDT_HAS_SEMAPHORES let's systemtap (sys/sdt.h) know that we want to
24// use the optional semaphore feature for our tracepoints. This feature allows
25// us to check if something is attached to a tracepoint. We only want to prepare
26// some potentially expensive tracepoint arguments, if the tracepoint is being
27// used. Here, an expensive argument preparation could, for example, be
28// calculating a hash or serialization of a data structure.
29#define _SDT_HAS_SEMAPHORES 1
30
31// Used to define a counting semaphore for a tracepoint. This semaphore is
32// automatically incremented by tracing frameworks (bpftrace, bcc, libbpf, ...)
33// upon attaching to the tracepoint and decremented when detaching. This needs
34// to be a global variable. It's placed in the '.probes' ELF section.
35#define TRACEPOINT_SEMAPHORE(context, event) \
36    unsigned short context##_##event##_semaphore __attribute__((section(".probes")))
37
38#include <sys/sdt.h>
39
40// Returns true if something is attached to the tracepoint.
41#define TRACEPOINT_ACTIVE(context, event) (context##_##event##_semaphore > 0)
42
43// A USDT tracepoint with one to twelve arguments. It's checked that the
44// tracepoint is active before preparing its arguments.
45#define TRACEPOINT(context, event, ...)                                         \
46    do {                                                                        \
47        if (TRACEPOINT_ACTIVE(context, event)) {                                \
48            STAP_PROBEV(context, event __VA_OPT__(, ) __VA_ARGS__);             \
49        }                                                                       \
50    } while(0)
51
52#else
53
54#define TRACEPOINT_SEMAPHORE(context, event)
55#define TRACEPOINT_ACTIVE(context, event) false
56#define TRACEPOINT(context, ...)
57
58#endif // ENABLE_TRACING
59
60
61#endif // BITCOIN_UTIL_TRACE_H
62