Re: [PATCH] modpost: return error if module is missing ns imports and MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS=n

[Jessica Yu]

+++ 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@xxxxxxxxxx>
> > ---
> > 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?

> > +				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 $(KBUILD_MODPOST_WARN),-w)

ifdef MODPOST_VMLINUX

Thanks for the review!