[PATCH v3 15/15] kbuild: make *.mod rule robust against too long argument error

[Nicolas Schier]

On Thu, May 05, 2022 at 04:22:44PM +0900 Masahiro Yamada wrote:
> Like built-in.a, the command length of the *.mod rule scales with
> the depth of the directory times the number of objects in the Makefile.
> 
> Add $(obj)/ by the shell command (awk) instead of by Make's builtin
> function.
> 
> In-tree modules still have some room to the limit (ARG_MAX=2097152),
> but this is more future-proof for big modules in a deep directory.
> 
> For example, you can build i915 as a module (CONFIG_DRM_I915=m) and
> compare drivers/gpu/drm/i915/.i915.mod.cmd with/without this commit.
> 
> The issue is more critical for external modules because the M= path
> can be very long as Jeff Johnson reported before [1].
> 
> [1] https://lore.kernel.org/linux-kbuild/4c02050c4e95e4cb8cc04282695f8404@codeaurora.org/
> 
> Signed-off-by: Masahiro Yamada <masahiroy at kernel.org>
> ---
> 
> (no changes since v2)
> 
> Changes in v2:
>   - New patch
> 
>  scripts/Makefile.build | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index cea48762299c..e7b3f329d443 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -266,8 +266,8 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
>  	$(call if_changed_rule,cc_o_c)
>  	$(call cmd,force_checksrc)
>  
> -cmd_mod = echo $(addprefix $(obj)/, $(call real-search, $*.o, .o, -objs -y -m)) | \
> -	$(AWK) -v RS='( |\n)' '!x[$$0]++' > $@
> +cmd_mod = echo $(call real-search, $*.o, .o, -objs -y -m) | \
> +	$(AWK) -v RS='( |\n)' '!x[$$0]++ { print("$(obj)/"$$0) }' > $@
>  
>  $(obj)/%.mod: FORCE
>  	$(call if_changed,mod)
> -- 
> 2.32.0

Thanks!  At work, some colleagues of mine stumbled over that problem, too.

Reviewed-by: Nicolas Schier <nicolas at fjasle.eu>