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