linux-kernel - Re: [PATCH] tracing: Fix DECLARE_TRACE

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Message-ID: <2660636b8e9d14f905b161cdf499082952bd2030.camel@redhat.com>
Date: Tue, 28 Jan 2025 12:30:47 +0100
From: Gabriele Monaco <gmonaco@...hat.com>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Cc: Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>,  Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] tracing: Fix DECLARE_TRACE_CONDITION

On Tue, 2025-01-28 at 12:19 +0100, Gabriele Monaco wrote:
> Commit 287050d39026 ("tracing: Add TRACE_EVENT_CONDITIONAL()") adds
> macros to define conditional trace events (TRACE_EVENT_CONDITIONAL)
> and
> tracepoints (DECLARE_TRACE_CONDITION), but sets up functionality for
> direct use only for the former.
> Any attempt to use DECLARE_TRACE_CONDITION fails the build.
> 
> Add preprocessor bits in define_trace.h to allow usage of
> DECLARE_TRACE_CONDITION just like DECLARE_TRACE.
> 
> Fixes: 287050d39026 ("tracing: Add TRACE_EVENT_CONDITIONAL()")
> Signed-off-by: Gabriele Monaco <gmonaco@...hat.com>
> ---

The macro is currently never used, I'm planning to use it in a future
patch.
Likewise also DECLARE_TRACE_SYSCALL is never used and would fail the
build if used. I'm not sure if the macro would be of use in this way,
since it's missing the reg and unreg parameters used in
DEFINE_TRACE_SYSCALL, one way not to fail the build is to treat it just like
DECLARE_TRACE (as DECLARE_TRACE_CONDITION).
I can prepare this as a patch if it's the intended behaviour:

diff --git a/include/trace/define_trace.h b/include/trace/define_trace.h
index ed52d0506c69..497a5a2469dc 100644
--- a/include/trace/define_trace.h
+++ b/include/trace/define_trace.h
@@ -80,6 +80,10 @@
 #define DECLARE_TRACE_CONDITION(name, proto, args, cond)	\
 	DEFINE_TRACE(name, PARAMS(proto), PARAMS(args))
 
+#undef DECLARE_TRACE_SYSCALL
+#define DECLARE_TRACE_SYSCALL(name, proto, args, cond)	\
+	DEFINE_TRACE(name, PARAMS(proto), PARAMS(args))
+
 /* If requested, create helpers for calling these tracepoints from Rust. */
 #ifdef CREATE_RUST_TRACE_POINTS
 #undef DEFINE_RUST_DO_TRACE
@@ -114,6 +118,8 @@
 #define DECLARE_TRACE(name, proto, args)
 #undef DECLARE_TRACE_CONDITION
 #define DECLARE_TRACE_CONDITION(name, proto, args, cond)
+#undef DECLARE_TRACE_SYSCALL
+#define DECLARE_TRACE_SYSCALL(name, proto, args, cond)
 
 #ifdef TRACEPOINTS_ENABLED
 #include <trace/trace_events.h>
@@ -136,6 +142,7 @@
 #undef TRACE_HEADER_MULTI_READ
 #undef DECLARE_TRACE
 #undef DECLARE_TRACE_CONDITION
+#undef DECLARE_TRACE_SYSCALL
 
 /* Only undef what we defined in this file */
 #ifdef UNDEF_TRACE_INCLUDE_FILE