linux-kernel - Re: [PATCH v4 1/4] tracing: sorttable: Add a tracepoint verification check at build time

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Message-ID: <20250723182701.195a5ddf@gandalf.local.home>
Date: Wed, 23 Jul 2025 18:27:01 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Steven Rostedt <rostedt@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
 llvm@...ts.linux.dev, Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
 <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.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>
Subject: Re: [PATCH v4 1/4] tracing: sorttable: Add a tracepoint
 verification check at build time

On Wed, 23 Jul 2025 13:31:52 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, 23 Jul 2025 at 12:42, Steven Rostedt <rostedt@...nel.org> wrote:
> >
> >  kernel/trace/Kconfig              |  19 +++  
> 
> Annoying "one step forward, two steps back" change.
> 
> You literally sent a "remove one pointless Kconfig option" patch
> within ten minutes of sending out this "add two pointless Kconfig
> options" patch.

You mean to also get rid of the TRACEPOINT_VERIFY_USED config?

> 
> Because as long as it's a build-time thing, please just fix the
> problems it points out, and it should have no real cost to being
> enabled.
> 
> We don't want to ask people questions that don't matter.
> 
> Of course, because you *used* to check this at run-time, you put the
> new "__tracepoint_check" table in a section that is actually loaded
> into memory, and it appears to be still there.
> 
> Just put it in the discard section, the same way we have (for example)
> the export_symbols table that we also check at build-time without
> actually ever making it part of the kernel.

Ah, I wasn't sure how to do that. So you are saying to do:

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 600d8b51e315..365c92e6d0ce 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -1048,6 +1047,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
 	*(.modinfo)							\
 	/* ld.bfd warns about .gnu.version* even when not emitted */	\
 	*(.gnu.version*)						\
+	*(.__tracepoint_check)
 
 #define DISCARDS							\
 	/DISCARD/ : {							\


But this will require that I change how it's done, as it doesn't look like
it's available when sorttable.c is used.

Looks like it will require a separate application to search the vmlinux.o
instead of the vmlinux (which sorttable does).

I could probably take some of the sorttable.c elf parsing and move that
into a header that would share the code.

-- Steve