linux-kernel - Re: [PATCH] kbuild: install-extmod-build: do not exclude scripts/dtc/libfdt/

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Message-ID: <ed9cd9a5d1f51b83c46ada7adb942e611c0c8a41.camel@icenowy.me>
Date: Wed, 04 Feb 2026 11:27:24 +0800
From: Icenowy Zheng <uwu@...nowy.me>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Nicolas Schier <nsc@...nel.org>, Masahiro Yamada <masahiroy@...nel.org>,
  Abel Vesa <abelvesa@...nel.org>, Mingcong Bai <jeffbai@...c.io>, WangYuli
 <wangyuli@...ontech.com>,  Inochi Amaoto <inochiama@...il.com>, James Le
 Cuirot <chewi@...too.org>, linux-kbuild@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Rong Zhang <i@...g.moe>, Rob Herring
 <robh@...nel.org>, Saravana Kannan <saravanak@...nel.org>, 
 devicetree@...r.kernel.org
Subject: Re: [PATCH] kbuild: install-extmod-build: do not exclude
 scripts/dtc/libfdt/

在 2026-02-04星期三的 11:26 +0800，Icenowy Zheng写道：
> 在 2026-02-03星期二的 19:16 -0700，Nathan Chancellor写道：
> > + Rob, Saravana, and devicetree@ since this concerns files they
> > own.
> > 
> > On Sun, Feb 01, 2026 at 09:02:59PM +0800, Icenowy Zheng wrote:
> > > There exists a header file in include/linux/ called libfdt.h that
> > > is
> > > just a wrapper for libfdt header file in scripts/dtc/libfdt/.
> > > This
> > > makes
> > > the headers inside libfdt copy at scripts/dtc/libfdt/ part of the
> > > kernel
> > > headers for building external modules.
> > > 
> > > Do not exclude them, otherwise modules that include
> > > <linux/libfdt.h>
> > > will fail to build externally.
> > > 
> > > Fixes: aaed5c7739be ("kbuild: slim down package for building
> > > external modules")
> > > Signed-off-by: Icenowy Zheng <zhengxingda@...as.ac.cn>
> > 
> > This does indeed bring back scripts/dtc/libfdt back into the
> > headers
> > package that I examined. However, how does including libfdt.h in an
> > external module actually work, even with this change? libfdt
> > appears
> > to
> > be built into vmlinux IIUC and I do not see any EXPORT_SYMBOLs in
> > the
> > list, so how can you actually use any of the functions from libfdt
> > within the module? Would you just build and link the pieces that
> > your
> > module needs using the other source files?
> 
> To be honest what I met is quite weird -- my module [1] does not use
> libfdt at all. However, as a MIPS platform-specific module, it
> includes
> arch/mips/include/asm/bootinfo.h, which pulls in libfdt.h.
> 
> Or maybe I should prevent libfdt.h inclusion from other kernel
> headers?
> It looks like only two headers in MIPS architecture-specific code
> includes libfdt.h, asm/bootinfo.h and asm/machine.h .
> 
> Thanks,
> Icenowy

Ah, forgot to place the [1] reference link, although I doubt whether
it's really related to the context:

[1] https://github.com/Icenowy/mips-loong-3nod-laptop-driver

> 
> > 
> > > ---
> > >  scripts/package/install-extmod-build | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/scripts/package/install-extmod-build
> > > b/scripts/package/install-extmod-build
> > > index 2576cf7902dbb..d1e448d7f59f6 100755
> > > --- a/scripts/package/install-extmod-build
> > > +++ b/scripts/package/install-extmod-build
> > > @@ -11,7 +11,8 @@ is_enabled() {
> > >  
> > >  find_in_scripts() {
> > >         find scripts \
> > > -               \( -name atomic -o -name dtc -o -name kconfig -o
> > > -
> > > name package \) -prune -o \
> > > +               \( -name atomic -o -name kconfig -o -name package
> > > -
> > > o \
> > > +                  \( -path '*/dtc/*' -a ! -path '*/libfdt*' \)
> > > \)
> > > -prune -o \
> > >                 ! -name unifdef -a ! -name mk_elfconfig -a \( -
> > > type
> > > f -o -type l \) -print
> > >  }
> > >  
> > > -- 
> > > 2.52.0
> > > 
>