[PATCH v13 2/5] modpost: Produce extended MODVERSIONS information

Matthew Maurer
2025-01-03T17:37:08Z

Generate both the existing modversions format and the new extended one
when running modpost. Presence of this metadata in the final .ko is
guarded by CONFIG_EXTENDED_MODVERSIONS.

We no longer generate an error on long symbols in modpost if
CONFIG_EXTENDED_MODVERSIONS is set, as they can now be appropriately
encoded in the extended section. These symbols will be skipped in the
previous encoding. An error will still be generated if
CONFIG_EXTENDED_MODVERSIONS is not set.

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
kernel/module/Kconfig | 10 ++++++++
scripts/Makefile.modpost | 1 +
scripts/mod/modpost.c | 62 ++++++++++++++++++++++++++++++++++++++++++++----
3 files changed, 69 insertions(+), 4 deletions(-)

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index d443fc504ffca0d1001f880ec496ab1f21fe979e..9568b629a03ce8289d3f3597eefc66fc96445720 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -207,6 +207,16 @@ config ASM_MODVERSIONS
assembly. This can be enabled only when the target architecture
supports it.

+config EXTENDED_MODVERSIONS
+ bool "Extended Module Versioning Support"
+ depends on MODVERSIONS
+ help
+ This enables extended MODVERSIONs support, allowing long symbol
+ names to be versioned.
+
+ The most likely reason you would enable this is to enable Rust
+ support. If unsure, say N.
+
config MODULE_SRCVERSION_ALL
bool "Source checksum for all modules"
help
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index ab0e94ea62496e11dbaa3ffc289ce546862795ca..40426fc6350985780c0092beb49c6cc29b9eff62 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_EXTENDED_MODVERSIONS),-x) \
$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a) \
$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E) \
$(if $(KBUILD_MODPOST_WARN),-w) \
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index e489983bb8b2850c0f95bcbdfd82f684d4e7f0c3..6324b30f6b97ac24dc517b9229f227c6c369f7d5 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -33,6 +33,8 @@ static bool module_enabled;
static bool modversions;
/* Is CONFIG_MODULE_SRCVERSION_ALL set? */
static bool all_versions;
+/* Is CONFIG_EXTENDED_MODVERSIONS set? */
+static bool extended_modversions;
/* If we are modposting external module set to 1 */
static bool external_module;
/* Only warn about unresolved symbols */
@@ -1804,6 +1806,49 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
}
}

+/**
+ * Record CRCs for unresolved symbols, supporting long names
+ */
+static void add_extended_versions(struct buffer *b, struct module *mod)
+{
+ struct symbol *s;
+
+ if (!extended_modversions)
+ return;
+
+ buf_printf(b, "\n");
+ buf_printf(b, "static const u32 ____version_ext_crcs[]\n");
+ buf_printf(b, "__used __section(\"__version_ext_crcs\") = {\n");
+ list_for_each_entry(s, &mod->unresolved_symbols, list) {
+ if (!s->module)
+ continue;
+ if (!s->crc_valid) {
+ warn("\"%s\" [%s.ko] has no CRC!\n",
+ s->name, mod->name);
+ continue;
+ }
+ buf_printf(b, "\t0x%08x,\n", s->crc);
+ }
+ buf_printf(b, "};\n");
+
+ buf_printf(b, "static const char ____version_ext_names[]\n");
+ buf_printf(b, "__used __section(\"__version_ext_names\") =\n");
+ list_for_each_entry(s, &mod->unresolved_symbols, list) {
+ if (!s->module)
+ continue;
+ if (!s->crc_valid)
+ /*
+ * 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.
+ */
+ continue;
+ buf_printf(b, "\t\"%s\\0\"\n", s->name);
+ }
+ buf_printf(b, ";\n");
+}
+
/**
* Record CRCs for unresolved symbols
**/
@@ -1827,9 +1872,14 @@ static void add_versions(struct buffer *b, struct module *mod)
continue;
}
if (strlen(s->name) >= MODULE_NAME_LEN) {
- error("too long symbol \"%s\" [%s.ko]\n",
- s->name, mod->name);
- break;
+ if (extended_modversions) {
+ /* this symbol will only be in the extended info */
+ continue;
+ } else {
+ error("too long symbol \"%s\" [%s.ko]\n",
+ s->name, mod->name);
+ break;
+ }
}
buf_printf(b, "\t{ 0x%08x, \"%s\" },\n",
s->crc, s->name);
@@ -1960,6 +2010,7 @@ static void write_mod_c_file(struct module *mod)
add_header(&buf, mod);
add_exported_symbols(&buf, mod);
add_versions(&buf, mod);
+ add_extended_versions(&buf, mod);
add_depends(&buf, mod);

buf_printf(&buf, "\n");
@@ -2125,7 +2176,7 @@ 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:")) != -1) {
+ while ((opt = getopt(argc, argv, "ei:MmnT:to:au:WwENd:x")) != -1) {
switch (opt) {
case 'e':
external_module = true;
@@ -2174,6 +2225,9 @@ int main(int argc, char **argv)
case 'd':
missing_namespace_deps = optarg;
break;
+ case 'x':
+ extended_modversions = true;
+ break;
default:
exit(1);
}

--
2.47.1.613.gc27f4b7a9f-goog