linux-kernel - Re: [PATCH v9 01/16] tracing: move function tracer options to Kconfig (causing parisc build failures)

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Message-ID: <CABCJKufph4se58eiJNSJUd3ASBgbJGmL2e3wg4Jwo4Bi2UxP=Q@mail.gmail.com>
Date:   Wed, 24 Feb 2021 12:54:15 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>, linux-parisc@...r.kernel.org,
        Helge Deller <deller@....de>
Subject: Re: [PATCH v9 01/16] tracing: move function tracer options to Kconfig
 (causing parisc build failures)

On Wed, Feb 24, 2021 at 12:38 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Wed, Feb 24, 2021 at 12:17:23PM -0800, Guenter Roeck wrote:
> > On Fri, Dec 11, 2020 at 10:46:18AM -0800, Sami Tolvanen wrote:
> > > Move function tracer options to Kconfig to make it easier to add
> > > new methods for generating __mcount_loc, and to make the options
> > > available also when building kernel modules.
> > >
> > > Note that FTRACE_MCOUNT_USE_* options are updated on rebuild and
> > > therefore, work even if the .config was generated in a different
> > > environment.
> > >
> > > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> > > Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> >
> > With this patch in place, parisc:allmodconfig no longer builds.
> >
> > Error log:
> > Arch parisc is not supported with CONFIG_FTRACE_MCOUNT_RECORD at scripts/recordmcount.pl line 405.
> > make[2]: *** [scripts/mod/empty.o] Error 2
> >
> > Due to this problem, CONFIG_FTRACE_MCOUNT_RECORD can no longer be
> > enabled in parisc builds. Since that is auto-selected by DYNAMIC_FTRACE,
> > DYNAMIC_FTRACE can no longer be enabled, and with it everything that
> > depends on it.
>
> Ew. Any idea why this didn't show up while it was in linux-next?

Does anyone build parisc allmodconfig from -next?

parisc seems to always use -fpatchable-function-entry with dynamic
ftrace, so we just need to select
FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY to stop it from defaulting
to recordmcount:

diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index ecef9aff9d72..9ee806f68123 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -60,6 +60,7 @@ config PARISC
        select HAVE_KPROBES
        select HAVE_KRETPROBES
        select HAVE_DYNAMIC_FTRACE if
$(cc-option,-fpatchable-function-entry=1,1)
+       select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY if HAVE_DYNAMIC_FTRACE
        select HAVE_FTRACE_MCOUNT_RECORD if HAVE_DYNAMIC_FTRACE
        select HAVE_KPROBES_ON_FTRACE
        select HAVE_DYNAMIC_FTRACE_WITH_REGS

I'll send a proper patch shortly.

Sami