linux-kernel - Re: [PATCH v3 4/4] tracing: move tracing declarations from kernel.h to a dedicated header

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Message-ID: <aUN8Hm377C5A0ILX@yury>
Date: Wed, 17 Dec 2025 22:59:33 -0500
From: Yury Norov <yury.norov@...il.com>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Christophe Leroy <chleroy@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	David Laight <david.laight@...box.com>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Andi Shyti <andi.shyti@...nel.org>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	Daniel Gomez <da.gomez@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>, linux-kernel@...r.kernel.org,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-modules@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v3 4/4] tracing: move tracing declarations from kernel.h
 to a dedicated header

On Tue, Dec 16, 2025 at 09:24:55PM -0800, Randy Dunlap wrote:
> [adding Kees]
> 
> On 12/16/25 4:13 PM, Andrew Morton wrote:
> > On Fri,  5 Dec 2025 12:52:35 -0500 "Yury Norov (NVIDIA)" <yury.norov@...il.com> wrote:
> > 
> >> Tracing is a half of the kernel.h in terms of LOCs, although it's
> >> a self-consistent part. It is intended for quick debugging purposes
> >> and isn't used by the normal tracing utilities.
> >>
> >> Move it to a separate header. If someone needs to just throw a
> >> trace_printk() in their driver, they will not have to pull all
> >> the heavy tracing machinery.
> >>
> >> This is a pure move, except for removing a few 'extern's.
> >>
> 
> Hm, for a pure move, this shouldn't be necessary. Anyway, not using
> FORTIFY in purgatory.o fixes this build error.
> Or maybe there's a better answer.
> 
> ---
>  arch/x86/purgatory/Makefile |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -62,7 +62,7 @@ PURGATORY_CFLAGS_REMOVE		+= $(CC_FLAGS_C
>  endif
>  
>  CFLAGS_REMOVE_purgatory.o	+= $(PURGATORY_CFLAGS_REMOVE)
> -CFLAGS_purgatory.o		+= $(PURGATORY_CFLAGS)
> +CFLAGS_purgatory.o		+= $(PURGATORY_CFLAGS) -D__NO_FORTIFY
>  
>  CFLAGS_REMOVE_sha256.o		+= $(PURGATORY_CFLAGS_REMOVE)
>  CFLAGS_sha256.o			+= $(PURGATORY_CFLAGS)

That happened because the new trace_printk.h includes string.h for
strlen(), so all kernel.h users now indirectly include it, and it
causes, seemingly, a circular dependency if FORTIFY is enabled.

A fix would be dropping trace_printk.h from kernel.h, or switching the
only user of string.h, trace_puts(), to __builtin_strlen().

Notice, Andy has concerned about this on the previous round, and also
suggested __builtin_strlen():

        https://lkml.org/lkml/2025/12/3/910

I deem to drop trace_printk.h from kernel.h - it is more aligned with
the idea of unloading the header. The original motivation to keep
trace_printk.h in kernel.h was just because a similar printk.h is living
there. But after all, this is a purely debugging header, so no need for
almost every C file to bear debugging stuff.

I can actually do both - switch to an intrinsic and drop the header.

Guys, please let me know what do you thing.

Thanks,
Yury