kbuild: Add gendwarfksyms as an alternative to genksyms

When MODVERSIONS is enabled, allow selecting gendwarfksyms as the
implementation, but default to genksyms.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

Author: samitolvanen

kernel/module/Kconfig

@@ -168,13 +168,36 @@ config MODVERSIONS
 	  make them incompatible with the kernel you are running.  If
 	  unsure, say N.
 
+choice
+	prompt "Module versioning implementation"
+	depends on MODVERSIONS
+	default GENKSYMS
+	help
+	  Select the tool used to calculate symbol versions for modules.
+
+	  If unsure, select GENKSYMS.
+
+config GENKSYMS
+	bool "genksyms (from source code)"
+	help
+	  Calculate symbol versions from pre-processed source code using
+	  genksyms.
+
+	  If unsure, say Y.
+
 config GENDWARFKSYMS
-	bool
+	bool "gendwarfksyms (from debugging information)"
 	depends on DEBUG_INFO
 	# Requires full debugging information, split DWARF not supported.
 	depends on !DEBUG_INFO_REDUCED && !DEBUG_INFO_SPLIT
 	# Requires ELF object files.
 	depends on !LTO
+	help
+	  Calculate symbol versions from DWARF debugging information using
+	  gendwarfksyms. Requires DEBUG_INFO to be enabled.
+
+	  If unsure, say N.
+endchoice
 
 config ASM_MODVERSIONS
 	bool

scripts/Makefile

@@ -53,7 +53,7 @@ hostprogs += unifdef
 targets += module.lds
 
 subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
-subdir-$(CONFIG_MODVERSIONS) += genksyms
+subdir-$(CONFIG_GENKSYMS) += genksyms
 subdir-$(CONFIG_GENDWARFKSYMS) += gendwarfksyms
 subdir-$(CONFIG_SECURITY_SELINUX) += selinux
 

scripts/Makefile.build

@@ -122,13 +122,22 @@ cmd_cpp_i_c       = $(CPP) $(c_flags) -o $@ $<
 $(obj)/%.i: $(obj)/%.c FORCE
 	$(call if_changed_dep,cpp_i_c)
 
+gendwarfksyms := scripts/gendwarfksyms/gendwarfksyms
+getexportsymbols = $(NM) $(1) | sed -n 's/.* __export_symbol_\(.*\)/$(2)/p'
+
 genksyms = scripts/genksyms/genksyms		\
 	$(if $(1), -T $(2))			\
 	$(if $(KBUILD_PRESERVE), -p)		\
 	-r $(or $(wildcard $(2:.symtypes=.symref)), /dev/null)
 
 # These mirror gensymtypes_S and co below, keep them in synch.
+ifdef CONFIG_GENDWARFKSYMS
+cmd_gensymtypes_c = $(if $(skip_gendwarfksyms),,			\
+	$(call getexportsymbols,$(2:.symtypes=.o),\1) |			\
+	$(gendwarfksyms) $(2:.symtypes=.o) $(if $(1), --symtypes $(2)))
+else
 cmd_gensymtypes_c = $(CPP) -D__GENKSYMS__ $(c_flags) $< | $(genksyms)
+endif # CONFIG_GENDWARFKSYMS
 
 quiet_cmd_cc_symtypes_c = SYM $(quiet_modtag) $@
       cmd_cc_symtypes_c = $(call cmd_gensymtypes_c,true,$@) >/dev/null
@@ -324,14 +333,27 @@ $(obj)/%.ll: $(obj)/%.rs FORCE
 # This is convoluted. The .S file must first be preprocessed to run guards and
 # expand names, then the resulting exports must be constructed into plain
 # EXPORT_SYMBOL(symbol); to build our dummy C file, and that gets preprocessed
-# to make the genksyms input.
+# to make the genksyms input or compiled into an object for gendwarfksyms.
 #
 # These mirror gensymtypes_c and co above, keep them in synch.
-cmd_gensymtypes_S =                                                         \
-   { echo "\#include <linux/kernel.h>" ;                                    \
-     echo "\#include <asm/asm-prototypes.h>" ;                              \
-     $(NM) $@ | sed -n 's/.* __export_symbol_\(.*\)/EXPORT_SYMBOL(\1);/p' ; } | \
-    $(CPP) -D__GENKSYMS__ $(c_flags) -xc - | $(genksyms)
+getasmexports =							\
+   { echo "\#include <linux/kernel.h>" ;			\
+     echo "\#include <linux/string.h>" ;			\
+     echo "\#include <asm/asm-prototypes.h>" ;			\
+     $(call getexportsymbols,$@,EXPORT_SYMBOL(\1);) ; }
+
+ifdef CONFIG_GENDWARFKSYMS
+cmd_gensymtypes_S =						\
+	$(getasmexports) |					\
+	$(CC) $(c_flags) -c -o $(@:.o=.gendwarfksyms.o) -xc -;	\
+	$(call getexportsymbols,$@,\1) |			\
+	$(gendwarfksyms) $(@:.o=.gendwarfksyms.o)		\
+		$(if $(1), --symtypes $(2))
+else
+cmd_gensymtypes_S =						\
+	$(getasmexports) |					\
+	$(CPP) -D__GENKSYMS__ $(c_flags) -xc - | $(genksyms)
+endif # CONFIG_GENDWARFKSYMS
 
 quiet_cmd_cc_symtypes_S = SYM $(quiet_modtag) $@
       cmd_cc_symtypes_S = $(call cmd_gensymtypes_S,true,$@) >/dev/null