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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Wed, 19 Feb 2020 04:27:09 +0900
Message-ID: <CAK7LNATBCE7j-FH3kFwHOjgjerjx8hziK9iWD5Av6wyweovewA@mail.gmail.com>
Subject: Re: [PATCH] modpost: return error if module is missing ns imports and MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS=n
To:     Jessica Yu <jeyu@kernel.org>
Cc:     Matthias Maennich <maennich@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Martijn Coenen <maco@android.com>
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On Wed, Feb 19, 2020 at 1:06 AM Jessica Yu <jeyu@kernel.org> wrote:
>
> +++ Matthias Maennich [17/02/20 14:56 +0000]:
> >Hi Jessica!
> >
> >On Fri, Feb 14, 2020 at 03:37:09PM +0100, Jessica Yu wrote:
> >>Currently when CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS=n, modpost only warns
> >>when a module is missing namespace imports. Under this configuration, such a module
> >>cannot be loaded into the kernel anyway, as the module loader would reject it.
> >>We might as well return a build error when a module is missing namespace imports
> >>under CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS=n, so that the build
> >>warning does not go ignored/unnoticed.
> >
> >I generally agree with the idea of the patch. Thanks for working on
> >this! I also can't remember any reason why I did not write it like this
> >initially. Probably just because I introduced this configuration option
> >quite late in the development process of the initial patches.
> >
> >>
> >>Signed-off-by: Jessica Yu <jeyu@kernel.org>
> >>---
> >>scripts/Makefile.modpost |  1 +
> >>scripts/mod/modpost.c    | 19 +++++++++++++++----
> >>2 files changed, 16 insertions(+), 4 deletions(-)
> >>
> >>diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> >>index b4d3f2d122ac..a53660f910a9 100644
> >>--- a/scripts/Makefile.modpost
> >>+++ b/scripts/Makefile.modpost
> >>@@ -53,6 +53,7 @@ MODPOST = scripts/mod/modpost                                               \
> >>      $(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS))) \
> >>      $(if $(KBUILD_EXTMOD),-o $(modulesymfile))                      \
> >>      $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)                  \
> >>+     $(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS),,-N)      \
> >>      $(if $(KBUILD_MODPOST_WARN),-w)
> >>
> >>ifdef MODPOST_VMLINUX
> >>diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> >>index 7edfdb2f4497..53e966f7d557 100644
> >>--- a/scripts/mod/modpost.c
> >>+++ b/scripts/mod/modpost.c
> >>@@ -39,6 +39,8 @@ static int sec_mismatch_count = 0;
> >>static int sec_mismatch_fatal = 0;
> >>/* ignore missing files */
> >>static int ignore_missing_files;
> >>+/* Return an error when there are missing namespace imports */
> >>+static int missing_ns_import_error = 0;
> >
> >A more suitable name is maybe missing_ns_import_is_error or follow the
> >naming of the config option: allow_missing_ns_imports (with default = 1).
> >
> >>
> >>enum export {
> >>      export_plain,      export_unused,     export_gpl,
> >>@@ -2216,9 +2218,15 @@ static int check_exports(struct module *mod)
> >>
> >>              if (exp->namespace &&
> >>                  !module_imports_namespace(mod, exp->namespace)) {
> >>-                     warn("module %s uses symbol %s from namespace %s, but does not import it.\n",
> >>-                          basename, exp->name, exp->namespace);
> >>-                     add_namespace(&mod->missing_namespaces, exp->namespace);
> >>+                     if (missing_ns_import_error) {
> >>+                             merror("module %s uses symbol %s from namespace %s, but does not import it.\n",
> >>+                                     basename, exp->name, exp->namespace);
> >
> >I would like to avoid the code duplication here. The string literal is
> >identical for both cases.
>
> Hm, but one is a call to merror() and the other to warn(). The
> previous if (warn_unresolved) block does the same thing. I am not sure
> how to simplify it to one call without introducing macro magic or
> overcomplicating things. Or were you thinking of something else?


I would not say this is a horrible duplication,
but if you avoid repeating the same string,
maybe you could do like this:

PRINTF log(enum loglevel loglevel, const char *fmt, ...)


BTW, you accidentally changed the indentation of
add_namespace(&mod->missing_namespaces, exp->namespace);


> >>+                             err = 1;
> >
> >Also, if we fail here, we might as well help the user to fix it by
> >suggesting to run `make nsdeps` (once per failed modpost run). Speaking
> >of which, `make nsdeps` is currently broken by this patch as it relies
> >on a successful (yet warning-full) build of the modules. So, in case of
> >`make nsdeps`, we probably have to omit the -N flag again when invoking
> >modpost.
>
> Good catch! Since KBUILD_NSDEPS is set when running `make nsdeps`,
> maybe we can do something like:
>
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index a53660f910a9..145703ef8d3a 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -53,7 +53,7 @@ MODPOST = scripts/mod/modpost                                         \
>         $(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS))) \
>         $(if $(KBUILD_EXTMOD),-o $(modulesymfile))                      \
>         $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)                  \
> -       $(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS),,-N)      \
> +       $(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS),,$(if $(KBUILD_NSDEPS),,-N))      \


If you follow Matthias' suggestion
"follow the naming of the config option: allow_missing_ns_imports
(with default = 1)."
the option is inverted, and you can write it more simply:


      $(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS)$(KBUILD_NSDEPS),-n)
     \


--
Best Regards
Masahiro Yamada