Re: [PATCH 06/12] selinux/genheaders: include bitsperlong and posix_types headers

[Nicolas Schier <nicolas@fjasle.eu>]

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Am Wed, Aug 07, 2024 at 09:41:00PM +0000 schrieb Daniel Gomez:
> Date: Wed, 7 Aug 2024 21:41:00 +0000
> From: Daniel Gomez <da.gomez@samsung.com>
> To: Nicolas Schier <nicolas@fjasle.eu>
> CC: Masahiro Yamada <masahiroy@kernel.org>, Nathan Chancellor
>  <nathan@kernel.org>, Lucas De Marchi <lucas.demarchi@intel.com>, Thomas
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>  <llvm@lists.linux.dev>, Finn Behrens <me@kloenk.dev>, "Daniel Gomez
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>  <gost.dev@samsung.com>
> Subject: Re: [PATCH 06/12] selinux/genheaders: include bitsperlong and
>  posix_types headers
> Message-ID: <sbj3c3tlafewy2n4pylbnpb4gwylpnyxovdykfy3dhk2wqmpry@ekhhe3mgqnd6>
> 
> On Wed, Aug 07, 2024 at 05:38:28PM GMT, Nicolas Schier wrote:
> > On Wed, Aug 07, 2024 at 01:09:20AM +0200, Daniel Gomez via B4 Relay wrote:
> > > From: Daniel Gomez <da.gomez@samsung.com>
> > > 
> > > The genheaders requires the bitsperlong.h and posix_types.h headers.
> > > To ensure these headers are found during compilation on macOS hosts,
> > > add usr/include to HOST_EXTRACFLAGS in the genheaders Makefile. This
> > > adjustment allows the compiler to locate all necessary headers when they
> > > are not available by default on macOS.
> > > 
> > > Signed-off-by: Daniel Gomez <da.gomez@samsung.com>
> > > ---
> > >  scripts/selinux/genheaders/Makefile | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/scripts/selinux/genheaders/Makefile b/scripts/selinux/genheaders/Makefile
> > > index 1faf7f07e8db..017149c90f8e 100644
> > > --- a/scripts/selinux/genheaders/Makefile
> > > +++ b/scripts/selinux/genheaders/Makefile
> > > @@ -2,4 +2,5 @@
> > >  hostprogs-always-y += genheaders
> > >  HOST_EXTRACFLAGS += \
> > >  	-I$(srctree)/include/uapi -I$(srctree)/include \
> > > -	-I$(srctree)/security/selinux/include
> > > +	-I$(srctree)/security/selinux/include \
> > > +	-I$(srctree)/usr/include
> > 
> > 'make headers' composes the UAPI header tree in $(objtree)/usr/include.
> > So, if you build out-of-source, -I$(srctree)/usr/include will not match.
> > Just remove the '$(srctree)/' prefix as '$(objtree)/' is always '.'.
> 
> The 'headers' target also deploys installs the headers in arch/$(SRCARCH)/
> include/uapi, so I've updated selinux/genheaders/Makefile to the following:
> 
> diff --git a/scripts/selinux/genheaders/Makefile b/scripts/selinux/genheaders/Makefile
> index 1faf7f07e8db..ae1f195b6f67 100644
> --- a/scripts/selinux/genheaders/Makefile
> +++ b/scripts/selinux/genheaders/Makefile
> @@ -2,4 +2,6 @@
>  hostprogs-always-y += genheaders
>  HOST_EXTRACFLAGS += \
>         -I$(srctree)/include/uapi -I$(srctree)/include \
> -       -I$(srctree)/security/selinux/include
> +       -I$(srctree)/security/selinux/include \
> +       -I$(objtree)/arch/$(SRCARCH)/include/generated/uapi \
> +       -I$(objtree)/arch/$(SRCARCH)/include/uapi

SRCARCH is not derived from the host but from $(ARCH) (cp. top-level
Makefile), thus you must not use arch/$(SRCARCH)/include/* for building
host progs as this breaks cross-building (e.g. consider build Linux for
32bit m68k on a arm64 host).

> 
> The include path -I$(objtree)/arch/$(SRCARCH)/include/generated/uapi
> enables locating the asm/types.h.
> 
> The include path -I$(objtree)/arch/$(SRCARCH)/include/uapi enables
> locating the asm/bitsperlong.h and asm/posix_types.h.
> 
> > 
> > But I am suspecting that this break cross-building.
> 
> I’ve tested this change on macOS with ARCH=arm64, as well as on Debian with
> ARCH=arm64 and ARCH=x86_64. Is it enough to just confirm that cross-building
> still works after this change?

No, it isn't.  asm/bitsperlong.h is probably similar (enough) for current
64-bit systems, but 32-bit platforms will have different versions.
Anyway, we must not use target arch/platform-specific header files for
host progs.  If we do, it will break.

You want to use arm64 specific header files for building your arm64 host
progs, as MacOS does not provide these (thus, it's a missing build
dependency).  As this is not common (yet), such a build hack should be limited
to MacOS/Darwin only to not accidentally break other platforms.  (Do you also
have MacOS/amd64 in mind?)

As written elsewhere, another approach could be to create and maintain a Linux
kernel dev kit for MacOS, that delivers (fetches, downloads, generates) all
missing header files.

Kind regards,
Nicolas


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