linux-kernel - Re: [PATCH] kbuild: error for CONFIG_ORC

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Message-ID: <20181217174936.ouhelssdkshclrr6@treble>
Date:   Mon, 17 Dec 2018 11:49:36 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Qian Cai <cai@....pw>
Cc:     yamada.masahiro@...ionext.com, michal.lkml@...kovi.net,
        mingo@...nel.org, bp@...en8.de, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH] kbuild: error for CONFIG_ORC_UNWINDER is too much

On Mon, Dec 17, 2018 at 12:13:59PM -0500, Qian Cai wrote:
> On Mon, 2018-12-17 at 11:03 -0600, Josh Poimboeuf wrote:
> > On Mon, Dec 17, 2018 at 11:17:28AM -0500, Qian Cai wrote:
> > > Since ifdef will be evaluated immediately in the first phrase of the
> > > Makefile read-in, there is no guarantee that the value for
> > > CONFIG_ORC_UNWINDER will be up-to-date until in the second phrase that
> > > this recipe is ran.
> > > 
> > > include/config/%.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd
> > > 	$(Q)$(MAKE) -f $(srctree)/Makefile syncconfig
> > > 
> > > Hence, change error to warning as this is essentially a best guess. The
> > > original bug can be reproduced this way,
> > 
> > But this still doesn't fix the root of the problem, that the check
> > relies on a stale auto.conf.
> > 
> 
> Yes, but it at least let people to be able to continue compiling kernel without
> prematurely being terminated incorrectly. The good thing is that that check will
> be triggered again to print out the right message once auto.conf has been synced
> up.
> 
> # make
> Makefile:966: "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please
> install libelf-dev, libelf-devel or elfutils-libelf-devel"
>   HOSTCC  scripts/kconfig/conf.o
>   HOSTLD  scripts/kconfig/conf
> scripts/kconfig/conf  --syncconfig Kconfig
> Makefile:968: "Cannot use CONFIG_STACK_VALIDATION=y, please install libelf-dev,
> libelf-devel or elfutils-libelf-devel"

Instead of giving false (or silent) warnings, why not just fix the real
problem?

Also the error exists for a reason: if the user misses the warning then
the ORC unwinder is broken and oops stack dumps are much less useful.

-- 
Josh