linux-kernel - Re: [Regression 4.15] Can't kill CONFIG_UNWINDER

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Message-ID: <20171229021323.GF10431@windriver.com>
Date:   Thu, 28 Dec 2017 21:13:24 -0500
From:   Paul Gortmaker <paul.gortmaker@...driver.com>
To:     Randy Dunlap <rdunlap@...radead.org>
CC:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        <linux-kbuild@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Regression 4.15] Can't kill CONFIG_UNWINDER_ORC with fire or
 plague.

[Re: [Regression 4.15] Can't kill CONFIG_UNWINDER_ORC with fire or plague.] On 28/12/2017 (Thu 11:29) Randy Dunlap wrote:

> On 12/25/2017 08:30 PM, Paul Gortmaker wrote:
> > There is a regression new to 4.15 that happens in a rather common
> > workflow which results in the frustrating situation where the user has
> > clearly disabled UNWINDER_ORC in their ".config" file, and yet they
> > still get the immediate false error saying they need libelf-dev since
> > "CONFIG_UNWINDER_ORC=y" is still set, and hence they can not build.
> > 
> > The regression requires UNWINDER_ORC=y (now the default in commit
> > fc72ae40e303) followed by the user subsequently disabling it, which is
> > common if the user doesn't have libelf-dev and doesn't care about ORC.
> > 
> > This happens because the recently added test in the top level Makefile
> > assumes that ,config data will be mapped into include/config/auto.conf
> > either by the end user running "make oldconfig" or the Makefile itself
> > detecting that "silentoldconfig" should be run.  As the simple
> > reproducer below shows, this clearly does not happen as expected.
> > 
> > Note that the test for CONFIG_STACK_VALIDATION and libelf-dev in the
> > same place in the Makefile is broken in the same way, but since it is a
> > warning and not an error, nobody cared about the bogus false positives.
> 
> Yeah, that's odd.
> 
> > Since there is no way I'm going to debug Makefile stuff on Christmas
> > Day, I figured that I should at least report it intstead.  The work
> > around is to save your .config and run a "make distclean" or manually
> > clobber the stale include/config/auto.conf or similar.  But a frustrated
> > user wouldn't know that w/o the root cause...
> > 
> 
> I have tried to reproduce this multiple times but cannot do so.
> It remains with:
> 
> > grep UNWINDER .config
> # CONFIG_UNWINDER_ORC is not set
> CONFIG_UNWINDER_FRAME_POINTER=y

As it should.  Please re-read the reproducer and the above.  The data in
the .config is exactly as it should be.  The include/config/auto.conf
having stale data with ORC still listed as enabled is the issue.

Also note you need a machine with libelf-dev not installed, at the risk
of stating the obvious.

Paul.
--

> 
> > 
> >     --------------------- reproducer ------------------------
> > 
> > paul@gw:~/git/linux-head$ git describe 
> > v4.15-rc5
> > paul@gw:~/git/linux-head$ make distclean 
> > paul@gw:~/git/linux-head$ make defconfig
> >   HOSTCC  scripts/basic/fixdep
> >   HOSTCC  scripts/kconfig/conf.o
> >   SHIPPED scripts/kconfig/zconf.tab.c
> >   SHIPPED scripts/kconfig/zconf.lex.c
> >   HOSTCC  scripts/kconfig/zconf.tab.o
> >   HOSTLD  scripts/kconfig/conf
> > *** Default configuration is based on 'x86_64_defconfig'
> > #
> > # configuration written to .config
> > #
> > paul@gw:~/git/linux-head$ make
> > scripts/kconfig/conf  --silentoldconfig Kconfig
> > Makefile:926: *** "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel".  Stop.
> > paul@gw:~/git/linux-head$ vi .config  # disable ORC in favour of FRAME_POINTER
> > paul@gw:~/git/linux-head$ make oldconfig
> > scripts/kconfig/conf  --oldconfig Kconfig
> > #
> > # configuration written to .config
> > #
> > paul@gw:~/git/linux-head$ grep UNWINDER .config
> > # CONFIG_UNWINDER_ORC is not set
> > CONFIG_UNWINDER_FRAME_POINTER=y
> > paul@gw:~/git/linux-head$ make
> > Makefile:926: *** "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel".  Stop.
> > paul@gw:~/git/linux-head$ ls -l .config include/config/auto.conf
> > -rw-rw-r-- 1 paul paul 115953 Dec 25 22:48 .config
> > -rw-rw-r-- 1 paul paul  33069 Dec 25 22:46 include/config/auto.conf
> > paul@gw:~/git/linux-head$ grep UNWINDER include/config/auto.conf
> > CONFIG_UNWINDER_ORC=y
> > paul@gw:~/git/linux-head$ 
> > 
> >     --------------------- reproducer ------------------------
> 
> 
> -- 
> ~Randy