FROMGIT: Documentation/kbuild: Document storage of symbol information

Document where exported and imported symbols are kept, format options,
and limitations.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
(cherry picked from commit 272f8a6d625a0cf7fba9c5af5202edc84dee326c
 https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git kbuild)
Bug: 347787665

Change-Id: I750a5bdf6233ec58fdf5bb0c9285247ee303a705
Signed-off-by: Matthew Maurer <mmaurer@google.com>

Documentation/kbuild/modules.rst

@@ -411,6 +411,26 @@ Symbols From the Kernel (vmlinux + modules)
 	1) It lists all exported symbols from vmlinux and all modules.
 	2) It lists the CRC if CONFIG_MODVERSIONS is enabled.
 
+Version Information Formats
+---------------------------
+
+	Exported symbols have information stored in __ksymtab or __ksymtab_gpl
+	sections. Symbol names and namespaces are stored in __ksymtab_strings,
+	using a format similar to the string table used for ELF. If
+	CONFIG_MODVERSIONS is enabled, the CRCs corresponding to exported
+	symbols will be added to the __kcrctab or __kcrctab_gpl.
+
+	If CONFIG_BASIC_MODVERSIONS is enabled (default with
+	CONFIG_MODVERSIONS), imported symbols will have their symbol name and
+	CRC stored in the __versions section of the importing module. This
+	mode only supports symbols of length up to 64 bytes.
+
+	If CONFIG_EXTENDED_MODVERSIONS is enabled (required to enable both
+	CONFIG_MODVERSIONS and CONFIG_RUST at the same time), imported symbols
+	will have their symbol name recorded in the __version_ext_names
+	section as a series of concatenated, null-terminated strings. CRCs for
+	these symbols will be recorded in the __version_ext_crcs section.
+
 Symbols and External Modules
 ----------------------------