[PATCH v4 18/19] kbuild: Add gendwarfksyms as an alternative to genksyms

Sami Tolvanen
2024-10-08T18:39:10Z

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

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Neal Gompa <neal@gompa.dev>
---
kernel/module/Kconfig | 25 ++++++++++++++++++++++++-
scripts/Makefile | 2 +-
scripts/Makefile.build | 39 +++++++++++++++++++++++++++++++--------
3 files changed, 56 insertions(+), 10 deletions(-)

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index f9e5f82fa88b..e6b2427e5c19 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -169,13 +169,36 @@ 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
diff --git a/scripts/Makefile b/scripts/Makefile
index d7fec46d38c0..8533f4498885 100644
--- a/scripts/Makefile
+++ b/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-$(CONFIG_SECURITY_SELINUX) += selinux
subdir-$(CONFIG_SECURITY_IPE) += ipe
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 8f423a1faf50..ae13afb71123 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -107,18 +107,28 @@ 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
+symtypes_dep_c = $(obj)/%.o
+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

-$(obj)/%.symtypes : $(obj)/%.c FORCE
+$(obj)/%.symtypes : $(obj)/%.c $(symtypes_dep_c) FORCE
$(call cmd,cc_symtypes_c)

# LLVM assembly
@@ -314,19 +324,32 @@ $(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>" ; \
+ $(call getexportsymbols,$(2:.symtypes=.o),EXPORT_SYMBOL(\1);) ; }
+
+ifdef CONFIG_GENDWARFKSYMS
+cmd_gensymtypes_S = \
+ $(getasmexports) | \
+ $(CC) $(c_flags) -c -o $(2:.symtypes=.gendwarfksyms.o) -xc -; \
+ $(call getexportsymbols,$(2:.symtypes=.o),\1) | \
+ $(gendwarfksyms) $(2:.symtypes=.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

-$(obj)/%.symtypes : $(obj)/%.S FORCE
+$(obj)/%.symtypes : $(obj)/%.S $(obj)/%.o FORCE
$(call cmd,cc_symtypes_S)