[PATCH v13 4/5] Documentation/kbuild: Document storage of symbol information

Matthew Maurer
2025-01-03T17:37:11Z

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

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
Documentation/kbuild/modules.rst | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)

diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst
index 101de236cd0c9abe1f5684d80063ff3f9a7fc673..a42f00d8cb90ff6ee44677c1278287ef25a84c89 100644
--- a/Documentation/kbuild/modules.rst
+++ b/Documentation/kbuild/modules.rst
@@ -423,6 +423,26 @@ 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
----------------------------

--
2.47.1.613.gc27f4b7a9f-goog