[PATCH v6 4/5] modpost: Produce extended MODVERSIONS information

[Matthew Maurer <mmaurer@google.com>]

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.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 kernel/module/Kconfig |  8 ++++++++
 scripts/mod/modpost.c | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index 7c6588148d42..a5de2b7f2758 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -177,6 +177,14 @@ 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 reasons you would enable
+	  this are for Rust usage or aggressive LTO configurations.
+
 config MODULE_SRCVERSION_ALL
 	bool "Source checksum for all modules"
 	help
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 107393a8c48a..d18ff8a1109a 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1840,15 +1840,56 @@ static void add_versions(struct buffer *b, struct module *mod)
 			continue;
 		}
 		if (strlen(s->name) >= MODULE_NAME_LEN) {
+#ifdef CONFIG_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;
+#endif
 		}
 		buf_printf(b, "\t{ %#8x, \"%s\" },\n",
 			   s->crc, s->name);
 	}
 
 	buf_printf(b, "};\n");
+
+	buf_printf(b, "#ifdef CONFIG_EXTENDED_MODVERSIONS\n");
+	buf_printf(b, "static const s32 ____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) {
+			/*
+			 * We already warned on this when producing the legacy
+			 * modversions table.
+			 */
+			continue;
+		}
+		buf_printf(b, "\t%#8x,\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 legacy
+			 * modversions 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");
+	buf_printf(b, "#endif\n");
 }
 
 static void add_depends(struct buffer *b, struct module *mod)
-- 
2.47.0.rc1.288.g06298d1525-goog