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Message-ID: <CAK7LNASbuJcgFBz+_4gJMnTvVeyeCbu2ZwGEu+ofj+kLKF9wiw@mail.gmail.com>
Date: Mon, 2 Sep 2024 00:33:57 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, linux-kernel@...r.kernel.org,
linux-kbuild@...r.kernel.org
Subject: Re: [PATCH RFC] modpost: compile constant module information only once
On Sun, Aug 25, 2024 at 2:44 AM Thomas Weißschuh <linux@...ssschuh.net> wrote:
>
> Various information about modules is compiled into the info sections.
> For that a dedicated .mod.c file is generated by modpost for each module
> and then linked into the module.
> However most of the information in the .mod.c is the same for all
> modules, internal and external.
> Split the shared information into a dedicated source file that is
> compiled once and then linked into all modules.
>
> This avoids frequent rebuilds for all .mod.c files when using
> CONFIG_LOCALVERSION_AUTO because the local version ends up in .mod.c
> through UTS_RELEASE and VERMAGIC_STRING.
> The modules are still relinked in this case.
>
> The code is also easier to maintain as it's now in a proper source file
> instead of an inline string literal.
>
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
> I came up with this while investigating something different.
> Not sure it's worth the effort.
> ---
> scripts/Makefile.modfinal | 9 +++++++--
> scripts/mod/modinfo.c | 25 +++++++++++++++++++++++++
> scripts/mod/modpost.c | 23 -----------------------
> scripts/package/install-extmod-build | 3 ++-
> 4 files changed, 34 insertions(+), 26 deletions(-)
>
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 306a6bb86e4d..dde09dc4ba11 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -30,6 +30,11 @@ quiet_cmd_cc_o_c = CC [M] $@
> %.mod.o: %.mod.c FORCE
> $(call if_changed_dep,cc_o_c)
>
> +ifeq ($(KBUILD_EXTMOD),)
> +scripts/mod/modinfo.o: scripts/mod/modinfo.c FORCE
> + $(call if_changed_dep,cc_o_c)
> +endif
> +
> quiet_cmd_ld_ko_o = LD [M] $@
> cmd_ld_ko_o += \
> $(LD) -r $(KBUILD_LDFLAGS) \
> @@ -54,13 +59,13 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check), \
> printf '%s\n' 'savedcmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
>
> # Re-generate module BTFs if either module's .ko or vmlinux changed
> -%.ko: %.o %.mod.o scripts/module.lds $(and $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),vmlinux) FORCE
> +%.ko: %.o %.mod.o scripts/module.lds scripts/mod/modinfo.o $(and $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),vmlinux) FORCE
> +$(call if_changed_except,ld_ko_o,vmlinux)
> ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +$(if $(newer-prereqs),$(call cmd,btf_ko))
> endif
>
> -targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o)
> +targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o) scripts/mod/modinfo.o
>
> # Add FORCE to the prerequisites of a target to force it to be always rebuilt.
> # ---------------------------------------------------------------------------
> diff --git a/scripts/mod/modinfo.c b/scripts/mod/modinfo.c
> new file mode 100644
> index 000000000000..12fbc6d3aae8
> --- /dev/null
> +++ b/scripts/mod/modinfo.c
> @@ -0,0 +1,25 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/module.h>
> +/*
> + * Include build-salt.h after module.h in order to
> + * inherit the definitions.
> + */
> +#define INCLUDE_VERMAGIC
> +#include <linux/build-salt.h>
> +#include <linux/elfnote-lto.h>
> +#include <linux/vermagic.h>
> +
> +#ifdef CONFIG_UNWINDER_ORC
> +#include <asm/orc_header.h>
> +ORC_HEADER;
> +#endif
> +
> +BUILD_SALT;
> +BUILD_LTO_INFO;
> +
> +MODULE_INFO(vermagic, VERMAGIC_STRING);
> +
> +#ifdef CONFIG_MITIGATION_RETPOLINE
> +MODULE_INFO(retpoline, "Y");
> +#endif
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index c8cd5d822bb6..107393a8c48a 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1755,26 +1755,9 @@ static void check_modname_len(struct module *mod)
> static void add_header(struct buffer *b, struct module *mod)
> {
> buf_printf(b, "#include <linux/module.h>\n");
> - /*
> - * Include build-salt.h after module.h in order to
> - * inherit the definitions.
> - */
> - buf_printf(b, "#define INCLUDE_VERMAGIC\n");
> - buf_printf(b, "#include <linux/build-salt.h>\n");
> - buf_printf(b, "#include <linux/elfnote-lto.h>\n");
> buf_printf(b, "#include <linux/export-internal.h>\n");
> - buf_printf(b, "#include <linux/vermagic.h>\n");
> buf_printf(b, "#include <linux/compiler.h>\n");
> buf_printf(b, "\n");
> - buf_printf(b, "#ifdef CONFIG_UNWINDER_ORC\n");
> - buf_printf(b, "#include <asm/orc_header.h>\n");
> - buf_printf(b, "ORC_HEADER;\n");
> - buf_printf(b, "#endif\n");
> - buf_printf(b, "\n");
> - buf_printf(b, "BUILD_SALT;\n");
> - buf_printf(b, "BUILD_LTO_INFO;\n");
> - buf_printf(b, "\n");
> - buf_printf(b, "MODULE_INFO(vermagic, VERMAGIC_STRING);\n");
> buf_printf(b, "MODULE_INFO(name, KBUILD_MODNAME);\n");
> buf_printf(b, "\n");
> buf_printf(b, "__visible struct module __this_module\n");
> @@ -1792,12 +1775,6 @@ static void add_header(struct buffer *b, struct module *mod)
> if (!external_module)
> buf_printf(b, "\nMODULE_INFO(intree, \"Y\");\n");
>
> - buf_printf(b,
> - "\n"
> - "#ifdef CONFIG_MITIGATION_RETPOLINE\n"
> - "MODULE_INFO(retpoline, \"Y\");\n"
> - "#endif\n");
> -
> if (strstarts(mod->name, "drivers/staging"))
> buf_printf(b, "\nMODULE_INFO(staging, \"Y\");\n");
>
> diff --git a/scripts/package/install-extmod-build b/scripts/package/install-extmod-build
> index d2c9cacecc0c..15fab6d5dd56 100755
> --- a/scripts/package/install-extmod-build
> +++ b/scripts/package/install-extmod-build
> @@ -37,6 +37,7 @@ mkdir -p "${destdir}"
> echo include/config/auto.conf
> echo include/config/kernel.release
> echo include/generated
> + echo scripts/mod/modinfo.o
> find_in_scripts
>
> if is_enabled CONFIG_GCC_PLUGINS; then
> @@ -78,4 +79,4 @@ if [ "${CC}" != "${HOSTCC}" ] && is_enabled CONFIG_CC_CAN_LINK; then
> rm -f "${destdir}/Kbuild" "${destdir}/scripts/Kbuild"
> fi
>
> -find "${destdir}" \( -name '.*.cmd' -o -name '*.o' \) -delete
> +find "${destdir}" \( -name '.*.cmd' -o \( -name '*.o' -a -! -path '*/scripts/mod/modinfo.o' \) \) -delete
This is not an enough hack because scripts/mod/modinfo.o
is a new requirement for building external modules.
'make clean' would need a similar treatment.
'make help' goes:
clean - Remove most generated files but keep the config and
enough build support to build external modules
Or, another approach is to generate a different object
when building external modules.
A patch attached (on top of this).
>
> ---
> base-commit: 184a282d540c3da03f6a229f4792a5f72d3dfc2a
> change-id: 20240824-modinfo-const-6f0d67e2b301
>
> Best regards,
> --
> Thomas Weißschuh <linux@...ssschuh.net>
>
--
Best Regards
Masahiro Yamada
View attachment "0001-fix.patch" of type "text/x-patch" (2933 bytes)
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