[PATCH v10 3/5] modules: Allow extended modversions without basic MODVERSIONS

[Matthew Maurer <mmaurer@google.com>]

If you know that your kernel modules will only ever be loaded by a newer
kernel, you can disable BASIC_MODVERSIONS to save space. This also
allows easy creation of test modules to seee how tooling will respond to
modules that only have the new format.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/Kconfig    | 15 +++++++++++++++
 scripts/Makefile.modpost |  1 +
 scripts/mod/modpost.c    | 19 +++++++++++--------
 3 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index a31c617cd67d3d66b24d2fba34cbd5cc9c53ab78..35545bc1d96016f95fe4e95e8876159a4a4d616d 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -218,6 +218,21 @@ config EXTENDED_MODVERSIONS
 	  The most likely reason you would enable this is to enable Rust
 	  support. If unsure, say N.
 
+config BASIC_MODVERSIONS
+	bool "Basic Module Versioning Support"
+	depends on MODVERSIONS
+	default MODVERSIONS
+	help
+	  This enables basic MODVERSIONS support, allowing older tools or
+	  kernels to potentially load modules.
+
+	  Disabling this may cause older `modprobe` or `kmod` to be unable
+	  to read MODVERSIONS information from built modules. With this
+	  disabled, older kernels may treat this module as unversioned.
+
+	  This is enabled by default when MODVERSIONS are enabled.
+	  If unsure, say Y.
+
 config MODULE_SRCVERSION_ALL
 	bool "Source checksum for all modules"
 	help
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 40426fc6350985780c0092beb49c6cc29b9eff62..d7d45067d08b94a82451d66a64eae29b6826e139 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -43,6 +43,7 @@ MODPOST = $(objtree)/scripts/mod/modpost
 modpost-args =										\
 	$(if $(CONFIG_MODULES),-M)							\
 	$(if $(CONFIG_MODVERSIONS),-m)							\
+	$(if $(CONFIG_BASIC_MODVERSIONS),-b)						\
 	$(if $(CONFIG_EXTENDED_MODVERSIONS),-x)						\
 	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)					\
 	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)					\
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index bd38f33fd41fbd98bce34f8924b2fb0ac04297ee..ed52f9aa45a490bba706ffb2caa3e238e4697814 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -32,6 +32,8 @@ static bool module_enabled;
 static bool modversions;
 /* Is CONFIG_MODULE_SRCVERSION_ALL set? */
 static bool all_versions;
+/* Is CONFIG_BASIC_MODVERSIONS set? */
+static bool basic_modversions;
 /* Is CONFIG_EXTENDED_MODVERSIONS set? */
 static bool extended_modversions;
 /* If we are modposting external module set to 1 */
@@ -1836,10 +1838,8 @@ static void add_extended_versions(struct buffer *b, struct module *mod)
 		if (!s->module)
 			continue;
 		if (!s->crc_valid) {
-			/*
-			 * We already warned on this when producing the legacy
-			 * modversions table.
-			 */
+			warn("\"%s\" [%s.ko] has no CRC!\n",
+				s->name, mod->name);
 			continue;
 		}
 		buf_printf(b, "\t%#8x,\n", s->crc);
@@ -1853,8 +1853,8 @@ static void add_extended_versions(struct buffer *b, struct module *mod)
 			continue;
 		if (!s->crc_valid) {
 			/*
-			 * We already warned on this when producing the legacy
-			 * modversions table.
+			 * We already warned on this when producing the crc
+			 * table.
 			 * We need to skip its name too, as the indexes in
 			 * both tables need to align.
 			 */
@@ -1872,7 +1872,7 @@ static void add_versions(struct buffer *b, struct module *mod)
 {
 	struct symbol *s;
 
-	if (!modversions)
+	if (!basic_modversions)
 		return;
 
 	buf_printf(b, "\n");
@@ -2184,7 +2184,7 @@ int main(int argc, char **argv)
 	LIST_HEAD(dump_lists);
 	struct dump_list *dl, *dl2;
 
-	while ((opt = getopt(argc, argv, "ei:MmnT:to:au:WwENd:x")) != -1) {
+	while ((opt = getopt(argc, argv, "ei:MmnT:to:au:WwENd:xb")) != -1) {
 		switch (opt) {
 		case 'e':
 			external_module = true;
@@ -2233,6 +2233,9 @@ int main(int argc, char **argv)
 		case 'd':
 			missing_namespace_deps = optarg;
 			break;
+		case 'b':
+			basic_modversions = true;
+			break;
 		case 'x':
 			extended_modversions = true;
 			break;

-- 
2.47.0.371.ga323438b13-goog