linux-kernel - Re: [PATCH 0/1] Add explicit error for missing CONFIG

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Date:   Tue, 22 Sep 2020 12:44:35 -0700
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH 0/1] Add explicit error for missing CONFIG_ASN1

On Tue, 2020-09-22 at 12:38 -0700, Randy Dunlap wrote:
> On 9/22/20 12:19 PM, James Bottomley wrote:
> > On Tue, 2020-09-22 at 11:54 -0700, Randy Dunlap wrote:
> > > On 9/22/20 8:53 AM, James Bottomley wrote:
> > > > I recently ran into this as an error from 0day.  On x86 it's
> > > > pretty
> > > > much impossible to build a configuration where CONFIG_ASN1
> > > > isn't
> > > > set, so you rarely notice a problem using the ASN.1 compiler
> > > > because something else has selected it.  However, this compiler
> > > > is
> > > > never built if CONFIG_ASN1 isn't set and the error you get from
> > > > kbuild is particularly unhelpful:
> > > > 
> > > >    make[4]: *** No rule to make target 'security/keys/trusted-
> > > > keys/tpm2key.asn1.o', needed by 'security/keys/trusted-
> > > > keys/built-
> > > > in.a'.
> > > >    make[4]: *** [scripts/Makefile.build:283:
> > > > security/keys/trusted-
> > > > keys/trusted_tpm2.o] Error 1
> > > >    make[4]: Target '__build' not remade because of errors.
> > > > 
> > > > This patch changes the above error to the much easier to
> > > > diagnose:
> > > > 
> > > >    scripts/Makefile.build:387: *** CONFIG_ASN1 must be defined
> > > > for
> > > > the asn1_compiler.  Stop.
> > > >    make[3]: *** [scripts/Makefile.build:505:
> > > > security/keys/trusted-
> > > > keys] Error 2
> > > > 
> > > > James
> > > > 
> > > > ---
> > > > 
> > > > James Bottomley (1):
> > > >   Makefile.build: Add an explicit error for missing ASN.1
> > > > compiler
> > > > 
> > > >  scripts/Makefile.build | 5 +++++
> > > >  1 file changed, 5 insertions(+)
> > > 
> > > Is there a missing
> > > 	select ASN1
> > > somewhere?
> > 
> > You mean in the build used to produce the errors above?  Yes, so
> > the
> > patch is to make the problem more explicit.
> 
> I appreciate that the message can be improved, but it seems possible
> that some Kconfig could also be improved.

I don't really see how.  To find the problem you have to identify a
conditional build in the Makefile that requires the asn1 compiler but
for which the config option doesn't have a select ASN1.  We don't
currently preserve the "what selected this symbol" information in
kconfig, which is what we'd need.

James