kbuild: Add CONFIG_MODVERSIONING and __kcrctab

This patch adds the new config option CONFIG_MODVERSIONING which will
be the new way of checking for ABI changes between kernel and module
code.

This and the following patches are in part based on an initial
implementation by Rusty Russell and I believe some of the ideas go back
to discussions on linux-kbuild, Keith Owens and Rusty.

though I'm not sure I think credit for the basic idea of
storing version info in sections goes to Keith Owens and Rusty.

o Rename __gpl_ksymtab to __ksymtab_gpl since that looks more consistent
  and appending _gpl instead of putting it into the middle simplifies
  sharing code for EXPORT_SYMBOL() and EXPORT_SYMBOL_GPL()
o Add CONFIG_MODVERSIONING
o If CONFIG_MODVERSIONING is set, add a section __kcrctab{,_gpl}, which
  contains the ABI checksums for the exported symbols listed in 
  __ksymtab{,_crc} Since we don't know the checksums yet at compilation
  time, just make them an unresolved symbol which gets filled in by the
  linker later.

1 files changed, 13 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index fcdd9fdb789601..5541908be8c043 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -144,6 +144,19 @@ config OBSOLETE_MODPARM
 	  have not been converted to the new module parameter system yet.
 	  If unsure, say Y.
 
+config MODVERSIONING
+	bool "Module versioning support (EXPERIMENTAL)"
+	depends on MODULES && EXPERIMENTAL
+	help
+	---help---
+	  Usually, you have to use modules compiled with your kernel.
+	  Saying Y here makes it sometimes possible to use modules
+	  compiled for different kernels, by adding enough information
+	  to the modules to (hopefully) spot any changes which would
+	  make them incompatible with the kernel you are running.  If
+	  you say Y here, you will need a copy of genksyms.  If
+	  unsure, say N.
+
 config KMOD
 	bool "Kernel module loader"
 	depends on MODULES