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

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Message-ID: <8017c328-f039-46c3-b472-f203cd6e2cfe@suse.com>
Date: Wed, 23 Oct 2024 16:59:00 +0200
From: Petr Pavlu <petr.pavlu@...e.com>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
 Luis Chamberlain <mcgrof@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Matthew Maurer <mmaurer@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>,
 Gary Guo <gary@...yguo.net>, Petr Pavlu <petr.pavlu@...e.com>,
 Daniel Gomez <da.gomez@...sung.com>, Neal Gompa <neal@...pa.dev>,
 Hector Martin <marcan@...can.st>, Janne Grunau <j@...nau.net>,
 Miroslav Benes <mbenes@...e.cz>, Asahi Linux <asahi@...ts.linux.dev>,
 Sedat Dilek <sedat.dilek@...il.com>, linux-kbuild@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v4 18/19] kbuild: Add gendwarfksyms as an alternative to
 genksyms

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@...gle.com>
> Acked-by: Neal Gompa <neal@...pa.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