Re: [RFC PATCH v2 3/5] kbuild: fit: Add opt-in FIT_FACTOR_DTBS support using fdtfactor

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] kbuild: fit: incomplete __local_fixups__ on composite DTBs
  with FIT_FACTOR_DTBS
--

commit b1fb21de907c618079fb42ef4673839c84598f6a
Author: Douglas Anderson <dianders@chromium.org>

kbuild: fit: Add opt-in FIT_FACTOR_DTBS support using fdtfactor

This commit adds opt-in support for factoring DTBs inside a compiled FIT
image into shared base DTBs and per-board overlays using fdtfactor when
FIT_FACTOR_DTBS is set.

> diff --git a/scripts/Makefile.dtbs b/scripts/Makefile.dtbs
> index cc14fc905ea3b..bc0c62617a7c2 100644
> --- a/scripts/Makefile.dtbs
> +++ b/scripts/Makefile.dtbs
> @@ -126,6 +126,14 @@ DTC_FLAGS += -Wnode_name_chars_strict \
>               -Wunique_unit_address
>  endif
>  
> +# When FIT_FACTOR_DTBS is set, pass -@ -L to dtc so the built DTBs retain the
> +# /__symbols__ and /__local_fixups__ nodes required by fdtfactor.
> +ifneq ($(FIT_FACTOR_DTBS),)
> +ifneq ($(filter arch/$(SRCARCH)/boot/dts%, $(obj)),)
> +DTC_FLAGS += -@ -L
> +endif
> +endif
> +
>  DTC_FLAGS += $(DTC_FLAGS_$(target-stem))
>  
>  # Set -@ if the target is a base DTB that overlay is applied onto
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index e08e35d4ed747..af2d3e5084249 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -418,6 +418,9 @@ quiet_cmd_uimage = UIMAGE  $@
>  # ---------------------------------------------------------------------------
>  
>  MAKE_FIT := $(srctree)/scripts/make_fit.py
> +# External fdtfactor tool from upstream dtc (requires matching pylibfdt)
> +FDTFACTOR ?= fdtfactor
> +FDTFACTOR_ARGS ?= --strip-local-fixups
>  
>  # Use this to override the compression algorithm
>  FIT_COMPRESSION ?= gzip
> @@ -428,7 +431,9 @@ quiet_cmd_fit = FIT     $@
>  		$(if $(findstring 1,$(KBUILD_VERBOSE)),-v) \
>  		$(if $(FIT_DECOMPOSE_DTBS),--decompose-dtbs) \
>  		$(if $(FIT_CONFIG_FILE),--config $(FIT_CONFIG_FILE)) \
> -		--compress $(FIT_COMPRESSION) -k $< @$(word 2,$^)
> +		--compress $(FIT_COMPRESSION) -k $< @$(word 2,$^) \
> +		$(if $(FIT_FACTOR_DTBS),&& $(FDTFACTOR) $(FDTFACTOR_ARGS) \
> +			$(if $(findstring 1,$(KBUILD_VERBOSE)),-s) -F $@)

[Severity: Medium]
As reported by Simon Glass on RFC [1], can composite DTBs built via
cmd_fdtoverlay reach fdtfactor with incomplete /__local_fixups__ when
FIT_FACTOR_DTBS=1 is used without FIT_DECOMPOSE_DTBS=1?

Although DTC_FLAGS passes -@ -L to dtc for the base .dtb and .dtbo inputs,
fdt_overlay_apply() in the in-tree scripts/dtc/libfdt/fdt_overlay.c merges
__overlay__ and __symbols__ into the target DTB without merging the
overlay's /__local_fixups__.  When FIT_DECOMPOSE_DTBS is not set,
make_fit.py packs those composite .dtb blobs into image.fit, leaving
fdtfactor without local fixup entries for phandle properties originating
from the overlays.

Until in-tree libfdt preserves overlay /__local_fixups__, should
FIT_FACTOR_DTBS imply --decompose-dtbs (or reject composite DTBs when
FIT_DECOMPOSE_DTBS is not enabled)?

[1] https://lore.kernel.org/r/CAFLszTh6vmFGVD4_Reewe9p4QqQjN=CVJ3SgfQKosAhedJpAQA@mail.gmail.com

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113210918.356261-1-dianders@chromium.org?part=3