tracepoints: gnu-zero-variadic-macro-arguments warnings

fanquake commented at 9:35 am on January 19, 2023: member

These occur for all tracepoints when using Clang 15 and a system installed systemtap:

 0# clang --version
 1Debian clang version 15.0.7
 2
 3./autogen.sh
 4./configure CC=clang-15 CXX=clang++-15
 5make
 6...
 7net_processing.cpp:4892:5: warning: must specify at least one argument for '...' parameter of variadic macro [-Wgnu-zero-variadic-macro-arguments]
 8    TRACE6(net, inbound_message,
 9    ^
10./util/trace.h:18:50: note: expanded from macro 'TRACE6'
11#define TRACE6(context, event, a, b, c, d, e, f) DTRACE_PROBE6(context, event, a, b, c, d, e, f)
12                                                 ^
13/usr/include/aarch64-linux-gnu/sys/sdt.h:494:3: note: expanded from macro 'DTRACE_PROBE6'
14  STAP_PROBE6(provider,probe,parm1,parm2,parm3,parm4,parm5,parm6)
15  ^
16/usr/include/aarch64-linux-gnu/sys/sdt.h:380:3: note: expanded from macro 'STAP_PROBE6'
17  _SDT_PROBE(provider, name, 6, (arg1, arg2, arg3, arg4, arg5, arg6))
18  ^
19/usr/include/aarch64-linux-gnu/sys/sdt.h:78:75: note: expanded from macro '_SDT_PROBE'
20    __asm__ __volatile__ (_SDT_ASM_BODY(provider, name, _SDT_ASM_ARGS, (n)) \
21                                                                          ^
22/usr/include/aarch64-linux-gnu/sys/sdt.h:283:9: note: macro '_SDT_ASM_BODY' defined here
23#define _SDT_ASM_BODY(provider, name, pack_args, args, ...)                   \
24        ^
251 warning generated.

hebasto commented at 10:59 am on January 23, 2023: member

FWIW, on Ubuntu Lunar with systemtap-sdt-dev-4.8 being installed, warnings are gone when configuring with --enable-c++20.

maflcko added the label Utils/log/libs on Jan 23, 2023

0xB10C commented at 12:04 pm on January 23, 2023: contributor

FWIW, on Ubuntu Lunar with systemtap-sdt-dev-4.8 being installed, warnings are gone when configuring with --enable-c++20.

fwiw I don’t think systemtap 4.8 is the reason there are no warnings for you. The changes form 4.7 to 4.8 in includes/sys/sdt.h file are minimal and shouldn’t affect this.

hebasto commented at 12:09 pm on January 23, 2023: member

FWIW, on Ubuntu Lunar with systemtap-sdt-dev-4.8 being installed, warnings are gone when configuring with --enable-c++20.

fwiw I don’t think systemtap 4.8 is the reason there are no warnings for you. The changes form 4.7 to 4.8 in includes/sys/sdt.h file are minimal and shouldn’t affect this.

Correct, the reason is --enable-c++20. See https://en.cppreference.com/w/cpp/preprocessor/replace.

fanquake closed this on Jan 26, 2023

fanquake reopened this on Jan 26, 2023

fanquake commented at 1:46 pm on January 26, 2023: member

Updated op to note that this is now system-installed systemtap only.

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willcl-ark commented at 11:08 am on March 23, 2023: member

This is still present with #26593 as it also uses an underlying variadic macro with 0 arguments via _SDT_ASM_BODY -> _SDT_PROBE -> _SDT_PROBE_N -> STAP_PROBEV -> TRACEPOINT.

I tried to directly call the STAP_PROBE1 macro for the single argument case (on top of #26593), which would mean that all our remaining TRACEPOINT macros were invoked with >= 1 argument:

0// A USDT tracepoint with one argument.
1#define TRACEPOINT1(context, event) \
2    if (TRACEPOINT_ACTIVE(context, event)) \
3        STAP_PROBE1(context, event, arg)

…but this apparently does not stop the warning, even though we are now never using an empty variadic argument:

 0wallet/spend.cpp:954:5: warning: must specify at least one argument for '...' parameter of variadic macro [-Wgnu-zero-variadic-macro-arguments]
 1    TRACEPOINT(coin_selection, selected_coins, wallet.GetName().c_str(), GetAlgorithmName(result.GetAlgo()).c_str(), result.GetTarget(), result.GetWaste(), result.GetSelectedValue());
 2    ^
 3./util/trace.h:48:9: note: expanded from macro 'TRACEPOINT'
 4        STAP_PROBEV(context, event, __VA_ARGS__)
 5        ^
 6/usr/include/x86_64-linux-gnu/sys/sdt.h:422:3: note: expanded from macro 'STAP_PROBEV'
 7  _SDT_PROBE_N(provider, name, _SDT_NARG(0, ##__VA_ARGS__), ##__VA_ARGS__)
 8  ^
 9/usr/include/x86_64-linux-gnu/sys/sdt.h:420:3: note: expanded from macro '_SDT_PROBE_N'
10  _SDT_PROBE(provider, name, N, (__VA_ARGS__))
11  ^
12/usr/include/x86_64-linux-gnu/sys/sdt.h:78:75: note: expanded from macro '_SDT_PROBE'
13    __asm__ __volatile__ (_SDT_ASM_BODY(provider, name, _SDT_ASM_ARGS, (n)) \
14                                                                          ^
15/usr/include/x86_64-linux-gnu/sys/sdt.h:289:9: note: macro '_SDT_ASM_BODY' defined here
16#define _SDT_ASM_BODY(provider, name, pack_args, args, ...)                   \
17        ^

It seems we have a few options therefore:

Do nothing and wait until we move to c++20 (no timeline)
Exclude the warning with global compile flags: CXXFLAGS += -Wno-gnu-zero-variadic-macro-arguments
Add pragmas inside the macros to disable the warnings (diff based on #26593):

 0diff --git a/src/util/trace.h b/src/util/trace.h
 1index 816d8c295..e3fc0d8f4 100644
 2--- a/src/util/trace.h
 3+++ b/src/util/trace.h
 4@@ -32,15 +32,29 @@
 5 #define TRACEPOINT_ACTIVE(context, event) context##_##event##_semaphore > 0
 6 
 7 // A USDT tracepoint with no arguments.
 8+// Remove pragmas when we switch to c++20
 9 #define TRACEPOINT0(context, event) \
10-    if (TRACEPOINT_ACTIVE(context, event)) \
11-        STAP_PROBE(context, event)
12+    do { \
13+        _Pragma("clang diagnostic push") \
14+        _Pragma("clang diagnostic ignored \"-Wgnu-zero-variadic-macro-arguments\"") \
15+        if (TRACEPOINT_ACTIVE(context, event)) { \
16+            STAP_PROBE(context, event); \
17+        } \
18+        _Pragma("clang diagnostic pop") \
19+    } while(0)
20 
21 // A USDT tracepoint with one to twelve arguments. It's checked that the
22 // tracepoint is active before preparing its arguments.
23+// Remove pragmas when we switch to c++20
24 #define TRACEPOINT(context, event, ...) \
25-    if (TRACEPOINT_ACTIVE(context, event)) \
26-        STAP_PROBEV(context, event, __VA_ARGS__)
27+    do { \
28+        _Pragma("clang diagnostic push") \
29+        _Pragma("clang diagnostic ignored \"-Wgnu-zero-variadic-macro-arguments\"") \
30+        if (TRACEPOINT_ACTIVE(context, event)) { \
31+            STAP_PROBEV(context, event, __VA_ARGS__); \
32+        } \
33+        _Pragma("clang diagnostic pop") \
34+    } while(0)
35 
36 #else

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tracepoints: gnu-zero-variadic-macro-arguments warnings #26916