linux-kernel - Re: [PATCH v10 08/11] build: Add modules.builtin.alias

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Message-ID: <ZG22iPLED+SJsEFa@bombadil.infradead.org>
Date:   Wed, 24 May 2023 00:02:32 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Allen Webb <allenwebb@...gle.com>
Cc:     "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        gregkh@...uxfoundation.org, christophe.leroy@...roup.eu,
        nick.alcock@...cle.com
Subject: Re: [PATCH v10 08/11] build: Add modules.builtin.alias

On Thu, Apr 06, 2023 at 02:00:27PM -0500, Allen Webb wrote:
> Generate modules.builtin.alias using modpost and install it with the
> modules.

Why? This is probably one of the more important commits and the
commit log is pretty slim.

> Signed-off-by: Allen Webb <allenwebb@...gle.com>
> ---
>  .gitignore               |  1 +
>  Makefile                 |  1 +
>  scripts/Makefile.modpost | 15 +++++++++++++++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/.gitignore b/.gitignore
> index 13a7f08a3d73..ddaa622bddac 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -71,6 +71,7 @@ modules.order
>  /System.map
>  /Module.markers
>  /modules.builtin
> +/modules.builtin.alias
>  /modules.builtin.modinfo
>  /modules.nsdeps
>  
> diff --git a/Makefile b/Makefile
> index a2c310df2145..43dcc1ea5fcf 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1578,6 +1578,7 @@ __modinst_pre:
>  	fi
>  	@sed 's:^\(.*\)\.o$$:kernel/\1.ko:' modules.order > $(MODLIB)/modules.order
>  	@cp -f modules.builtin $(MODLIB)/
> +	@cp -f modules.builtin.alias $(MODLIB)/
>  	@cp -f $(objtree)/modules.builtin.modinfo $(MODLIB)/
>  
>  endif # CONFIG_MODULES
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index 0980c58d8afc..e3ecc17a7a19 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -15,6 +15,7 @@
>  # 2) modpost is then used to
>  # 3)  create one <module>.mod.c file per module
>  # 4)  create one Module.symvers file with CRC for all exported symbols
> +# 5)  create modules.builtin.alias the aliases for built-in modules

Does everyone want that file?

>  # Step 3 is used to place certain information in the module's ELF
>  # section, including information such as:
> @@ -63,6 +64,20 @@ modpost-args += -T $(MODORDER)
>  modpost-deps += $(MODORDER)
>  endif
>  
> +ifneq ($(wildcard vmlinux.o),)
> +output-builtin.alias := modules.builtin.alias
> +modpost-args += -b .modules.builtin.alias.in
> +.modules.builtin.alias.in: $(output-symdump)
> +	@# Building $(output-symdump) generates .modules.builtin.alias.in as a
> +	@# side effect.
> +	@[ -e $@ ] || $(MODPOST) -b .modules.builtin.alias.in vmlinux.o

Does using -b create a delay in builds ? What is the effect on build
time on a typical 4-core or 8-core build? Does everyone want it?

Should we add a new option which lets people decide if they want this
at build time or not?

  Luis

> +
> +$(output-builtin.alias): .modules.builtin.alias.in
> +	sort -o $@ $^
> +
> +__modpost: $(output-builtin.alias)
> +endif
> +
>  ifeq ($(KBUILD_EXTMOD),)
>  
>  # Generate the list of in-tree objects in vmlinux
> -- 
> 2.39.2
>