linux-kernel - Re: [PATCH V4 2/3] scripts: dtc: Build fdtoverlay tool

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Date:   Tue, 19 Jan 2021 10:37:05 -0600
From:   Frank Rowand <frowand.list@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Bill Mills <bill.mills@...aro.org>, anmar.oueja@...aro.org,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH V4 2/3] scripts: dtc: Build fdtoverlay tool

Hi Viresh,

I made these comments in the v2 patch series.  I am copying them here since
this is the current version.

On 1/12/21 2:29 AM, Viresh Kumar wrote:
> We will start building overlays for platforms soon in the kernel and
> would need fdtoverlay going forward. Lets start building it.
> 
> The fdtoverlay program applies (or merges) one ore more overlay dtb
> blobs to a base dtb blob. The kernel build system would later use
> fdtoverlay to generate the overlaid blobs based on platform specific
> configurations.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  scripts/dtc/Makefile | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/dtc/Makefile b/scripts/dtc/Makefile
> index 4852bf44e913..5f19386a49eb 100644
> --- a/scripts/dtc/Makefile
> +++ b/scripts/dtc/Makefile
> @@ -1,13 +1,17 @@
>  # SPDX-License-Identifier: GPL-2.0
>  # scripts/dtc makefile
>  
> -hostprogs-always-$(CONFIG_DTC)		+= dtc
> +hostprogs-always-$(CONFIG_DTC)		+= dtc fdtoverlay
>  hostprogs-always-$(CHECK_DT_BINDING)	+= dtc
>  
>  dtc-objs	:= dtc.o flattree.o fstree.o data.o livetree.o treesource.o \
>  		   srcpos.o checks.o util.o
>  dtc-objs	+= dtc-lexer.lex.o dtc-parser.tab.o
>  

# The upstream project builds libfdt as a separate library.  We are choosing to
# instead directly link the libfdt object files into fdtoverly

> +libfdt-objs	:= fdt.o fdt_ro.o fdt_wip.o fdt_sw.o fdt_rw.o fdt_strerror.o fdt_empty_tree.o fdt_addresses.o fdt_overlay.o
> +libfdt		= $(addprefix libfdt/,$(libfdt-objs))
> +fdtoverlay-objs	:= $(libfdt) fdtoverlay.o util.o
> +
>  # Source files need to get at the userspace version of libfdt_env.h to compile
>  HOST_EXTRACFLAGS += -I $(srctree)/$(src)/libfdt
>  
> 

In general, I am a proponent of using shared libraries (which the upstream project
builds by default) because if a security bug in the library is fixed, it is fixed
for all users of the library.

In this specific case, I actually prefer the implementation that the patch provides
(directly linking the library object files into fdtoverlay, which uses the library)
because it is the only user of the library _and_ fdtoverlay will not inadvertently
use the system wide libfdt if it happens to be installed (as it is on my system).

Any thoughts on this Rob?

-Frank