Re: [PATCH v2] module: allow UNUSED_KSYMS_WHITELIST to be relative against objtree.

[Elliot Berman <quic_eberman@quicinc.com>]

On Wed, Apr 10, 2024 at 07:48:02PM +0000, Yifan Hong wrote:
> If UNUSED_KSYMS_WHITELIST is a file generated
> before Kbuild runs, and the source tree is in
> a read-only filesystem, the developer must put
> the file somewhere and specify an absolute
> path to UNUSED_KSYMS_WHITELIST. This worked,
> but if IKCONFIG=y, an absolute path is embedded
> into .config and eventually into vmlinux, causing
> the build to be less reproducible when building
> on a different machine.
> 
> This patch makes the handling of
> UNUSED_KSYMS_WHITELIST to be similar to
> MODULE_SIG_KEY.
> 
> First, check if UNUSED_KSYMS_WHITELIST is an
> absolute path, just as before this patch. If so,
> use the path as is.
> 
> If it is a relative path, use wildcard to check
> the existence of the file below objtree first.
> If it does not exist, fall back to the original
> behavior of adding $(srctree)/ before the value.
> 
> After this patch, the developer can put the generated
> file in objtree, then use a relative path against
> objtree in .config, eradicating any absolute paths
> that may be evaluated differently on different machines.
> 
> Signed-off-by: Yifan Hong <elsk@google.com>

I wonder if we should have a macro to do it so we can have a common
macro for the other time this is done for sig-key in
scripts/Makefile.modinst?

maybe-srctree = $(if $(wildcard $1),,$(srctree)/)$1

I'd let Masahiro/others decide if it's worth it. Otherwise,

Reviewed-by: Elliot Berman <quic_eberman@quicinc.com>

> ---
> V1 -> V2: properly handle absolute paths by treating
>   them as-is.
> 
>  kernel/module/Kconfig    | 2 +-
>  scripts/Makefile.modpost | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
> index f3e0329337f6..cb8377a18927 100644
> --- a/kernel/module/Kconfig
> +++ b/kernel/module/Kconfig
> @@ -392,7 +392,7 @@ config UNUSED_KSYMS_WHITELIST
>  	  exported at all times, even in absence of in-tree users. The value to
>  	  set here is the path to a text file containing the list of symbols,
>  	  one per line. The path can be absolute, or relative to the kernel
> -	  source tree.
> +	  source or obj tree.
>  
>  config MODULES_TREE_LOOKUP
>  	def_bool y
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index 739402f45509..36952638bbc6 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -94,7 +94,7 @@ targets += .vmlinux.objs
>  
>  ifdef CONFIG_TRIM_UNUSED_KSYMS
>  ksym-wl := $(CONFIG_UNUSED_KSYMS_WHITELIST)
> -ksym-wl := $(if $(filter-out /%, $(ksym-wl)),$(srctree)/)$(ksym-wl)
> +ksym-wl := $(if $(filter-out /%, $(ksym-wl)),$(if $(wildcard $(ksym-wl)),,$(srctree)/))$(ksym-wl)
>  modpost-args += -t $(addprefix -u , $(ksym-wl))
>  modpost-deps += $(ksym-wl)
>  endif
> -- 
> 2.44.0.478.gd926399ef9-goog
> 
>