linux-kernel - Re: [RFC][PATCH] kconfig: introduce listunknownconfig

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Message-ID: <20230820045829.GL907732@google.com>
Date:   Sun, 20 Aug 2023 13:58:29 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Jonathan Corbet <corbet@....net>,
        Tomasz Figa <tfiga@...omium.org>, linux-kbuild@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [RFC][PATCH] kconfig: introduce listunknownconfig

On (23/08/20 11:45), Sergey Senozhatsky wrote:
> > 
> > A new target is not what I like to see.
> > 
> > 
> > We decided to add KCONFIG_VERBOSE, which will be used to
> > warn options accidentally disabled or downgraded.
> 
> That doesn't seem cover the cases that I'm concerned with. I don't see
> anything related to "!sym" in the patch.
> 
> What will KCONFIG_VERBOSE do if it reads the following config file?
> 
> // assuming that both config options were valid and existed in the old
> // kernel, but were removed/renamed in the new kernel
> 
>  $ cat .config
>  CONFIG_DISABLE_BUGS=y
>  # CONFIG_ENABLE_WINAPI is not set
> 
> 
> I'd like to see warnings for both lines, even for config that is not
> set, because it maybe we set by a build script depending on USE flags
> for instance, so that build target may still refer to non-existent
> config.

It's also important to exit with an error when non-existent config symbols
are detected. Because that is an error. We are looking at a broken kernel
from the end user PoV: the kernel will compile, get rolled out and at some
point you'll start receiving bug reports of non-functioning peripheral
hardware and whatnot (e.g. some specific USB devices whose config symbol
has been renamed).

So `make FOO-config` should never succeed if old config contains unrecognized
symbols, it should never get to the compilation stage.

That is not what KCONFIG_VERBOSE does (at least in its current form),
as far as I can tell.