Re: [PATCH v5 18/19] kbuild: Add gendwarfksyms as an alternative to genksyms

[Masahiro Yamada <masahiroy@kernel.org>]

On Thu, Oct 31, 2024 at 2:01 AM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> 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 | 41 +++++++++++++++++++++++++++++++++--------
>  3 files changed, 58 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..d2a0440cdb79 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -107,18 +107,31 @@ cmd_cpp_i_c       = $(CPP) $(c_flags) -o $@ $<
>  $(obj)/%.i: $(obj)/%.c FORCE
>         $(call if_changed_dep,cpp_i_c)
>
> +getexportsymbols = $(NM) $(1) | sed -n 's/.* __export_symbol_\(.*\)/$(2)/p'
> +
> +gendwarfksyms = scripts/gendwarfksyms/gendwarfksyms    \
> +       $(if $(1), --symtypes $(2))                     \
> +       $(if $(KBUILD_GENDWARFKSYMS_STABLE), --stable)
> +
>  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))
> +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 +327,31 @@ $(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)


I do not want to see crazy suffix replacements like this.

I decided to delete this.
https://lore.kernel.org/linux-kbuild/20241111171753.2917697-2-masahiroy@kernel.org/T/#u



-- 
Best Regards
Masahiro Yamada