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

[Matthias Maennich <maennich@google.com>]

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.

>+				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.

Cheers,
Matthias

>+			} else {
>+				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 (!mod->gpl_compatible)
>@@ -2560,7 +2568,7 @@ int main(int argc, char **argv)
> 	struct ext_sym_list *extsym_iter;
> 	struct ext_sym_list *extsym_start = NULL;
>
>-	while ((opt = getopt(argc, argv, "i:e:mnsT:o:awEd:")) != -1) {
>+	while ((opt = getopt(argc, argv, "i:e:mnsT:o:awENd:")) != -1) {
> 		switch (opt) {
> 		case 'i':
> 			kernel_read = optarg;
>@@ -2598,6 +2606,9 @@ int main(int argc, char **argv)
> 		case 'E':
> 			sec_mismatch_fatal = 1;
> 			break;
>+		case 'N':
>+			missing_ns_import_error = 1;
>+			break;
> 		case 'd':
> 			missing_namespace_deps = optarg;
> 			break;
>-- 
>2.16.4
>