Message-ID: <14fc8777-a5d2-4877-9707-73c25d9e9bd3@infradead.org>
Date: Thu, 12 Jun 2025 20:20:48 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>, linux-arch@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Masami Hiramatsu <mhiramat@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor
 <nathan@...nel.org>, Nicolas Schier <nicolas.schier@...ux.dev>,
 Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
 Catalin Marinas <catalin.marinas@....com>,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 0/5] tracepoints: Add warnings for unused tracepoints
 and trace events

Hi,

On 6/12/25 4:58 PM, Steven Rostedt wrote:
> Every trace event can take up to 5K of memory in text and meta data regardless

s/meta data/metadata/ unless you are referring to meta's data.

s/meta data/metadata/ in patches 1 and 2 also.

> if they are used or not. Trace events should not be created if they are not
> used.  Currently there's over a hundred events in the kernel that are defined
> but unused, either because their callers were removed without removing the
> trace event with it, or a config hides the trace event caller but not the
> trace event itself. And in some cases, trace events were simply added but were
> never called for whatever reason. The number of unused trace events continues
> to grow.
> 
> This patch series aims to fix this.
> 
> The first patch creates a new section called __tracepoint_check, where all
> callers of a tracepoint creates a variable that is placed in this section with
> a pointer to the tracepoint they use. Then on boot up, it iterates this
> section and will modify the tracepoint's "func" field to a value of 1 (all
> tracepoints "func" fields are initialized to NULL and is only set when they
> are registered). This takes place before any tracepoint can be registered.
> 
> Then each tracepoint is iterated on and if any tracepoint does not have its
> "func" field set to 1 a warning is triggerd and every tracepoint that doesn't

triggered

> have that field set is printed. The "func" field is then reset back to NULL.
> 
> The second patch modifies scripts/sorttable.c to read the __tracepoint_check
> section. It sorts it, and then reads the __tracepoint_ptr section that has all
> compiled in tracepoints. It makes sure that every tracepoint is found in the
> check section and if not, it prints a warning message about it. This lists the
> missing tracepoints at build time.
> 
> The third patch updates sorttable to work for arm64 when compiled with gcc. As
> gcc's arm64 build doesn't put addresses in their section but saves them off in
> the RELA sections. This mostly takes the work done that was needed to do the
> mcount sorting at boot up on arm64.
> 
> The forth patch adds EXPORT_TRACEPOINT() to the __tracepoint_check section as

fourth (or are you coding in forth?)

> well. There was several locations that adds tracepoints in the kernel proper
> that are only used in modules. It was getting quite complex trying to move
> things around that I just decided to make any tracepoint in a
> EXPORT_TRACEPOINT "used". I'm using the analogy of static and global
> functions. An unused static function gets a warning but an unused global one
> does not.
> 
> The last patch updates the trace_ftrace_test_filter boot up self test. That
> selftest creates a trace event to run a bunch of filter tests on it without
> actually calling the tracepoint. To quiet the warning, the selftest tracepoint
> is called within a if (!trace_<event>_enabled()) section, where it will not be
> optimized out, nor will it be called.
> 
> This is v2 from: https://lore.kernel.org/linux-trace-kernel/20250529130138.544ffec4@gandalf.local.home/
> which was simply the first patch. This version adds the other patches.
> 
> Steven Rostedt (5):
>       tracepoints: Add verifier that makes sure all defined tracepoints are used
>       tracing: sorttable: Add a tracepoint verification check at build time
>       tracing: sorttable: Find unused tracepoints for arm64 that uses reloc for address
>       tracepoint: Do not warn for unused event that is exported
>       tracing: Call trace_ftrace_test_filter() for the event
> 
> ----
>  include/asm-generic/vmlinux.lds.h  |   1 +
>  include/linux/tracepoint.h         |  13 ++
>  kernel/trace/Kconfig               |  31 +++
>  kernel/trace/trace_events_filter.c |   4 +
>  kernel/tracepoint.c                |  26 +++
>  scripts/Makefile                   |   4 +
>  scripts/sorttable.c                | 444 ++++++++++++++++++++++++++++++-------
>  7 files changed, 437 insertions(+), 86 deletions(-)
> 

thanks.
-- 
~Randy

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