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

Petr Pavlu
2024-10-23T14:59:04Z

On 10/8/24 20:38, Sami Tolvanen 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 | 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)))

Is it possible to pass options to gendwarfksyms that apply to the entire
build, specifically, how can one say to use the --stable option? If not
then I think it would be good to add something as
KBUILD_GENDWARFKSYMS_STABLE (similar to KBUILD_PRESERVE), or maybe
a generic GENDWARFKSYMSFLAGS?

--
Thanks,
Petr