Re: [Buildroot] [PATCH 2/4] core: introduce NORMALIZED_ARCH as non-kernel replacement for KERNEL_ARCH

[Thomas De Schampheleire <patrickdepinguin@gmail.com>]

Hi Romain,

El jue, 13 ene 2022 a las 22:30, Romain Naour
(<romain.naour@gmail.com>) escribió:
>
> Le 18/05/2021 à 13:36, Thomas De Schampheleire a écrit :
> > From: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
> >
> > The variable 'KERNEL_ARCH' is actually a normalized version of
> > 'ARCH'/'BR2_ARCH'. For example, 'arcle' and 'arceb' both become 'arc', just
> > as all powerpc variants become 'powerpc'.
> >
> > It is presumably called 'KERNEL_ARCH' because the Linux kernel is typically
> > the first place where support for a new architecture is added, and thus is
> > the entity that defines the normalized name.
> >
> > However, the term 'KERNEL_ARCH' can also be interpreted as 'the architecture
> > used by the kernel', which need not be exactly the same as 'the normalized
> > name for a certain arch'. In particular, for cases where a 64-bit
> > architecture is running a 64-bit kernel but 32-bit userspace. Examples
> > include:
> >     * aarch64 architecture, with aarch64 kernel and 32-bit (ARM) userspace
> >     * x86_64 architecture, with x86_64 kernel and 32-bit (i386) userspace
> >
> > In such cases, the 'architecture used by the kernel' needs to refer to the
> > 64-bit name (aarch64, x86_64), whereas all userspace applications need to
> > refer the, potentially normalized, 32-bit name.
> >
> > This means that there need to be two different variables:
> >
> > KERNEL_ARCH:     the architecture used by the kernel
> > NORMALIZED_ARCH: the normalized name for the current userspace architecture
> >
> > At this moment, both will actually have the same content. But a subsequent
> > patch will add basic support for situations described above, in which
> > KERNEL_ARCH may become overwritten to the 64-bit architecture, while
> > NORMALIZED_ARCH needs to remain the same (32-bit) case.
> >
> > This commit replaces use of KERNEL_ARCH where actually the userspace arch is
> > needed.  Places that use KERNEL_ARCH in combination with building of kernel
> > modules are not touched.
> > There may be cases where a package builds both a kernel module as userspace,
> > in which case it may need to know about both KERNEL_ARCH and
> > NORMALIZED_ARCH, for the case where they differ. But this is to be fixed on
> > a per-need basis.
>
> While reviewing this patch, I noticed that LINUX_ARCH_PATH [1] is wrong for sparc64
>
> LINUX_ARCH_PATH = $(LINUX_DIR)/arch/$(KERNEL_ARCH)
>
> Indeed:
>
> $ make O=test/qemu_sparc64_sun4u_defconfig printvars VARS=LINUX_ARCH_PATH
> LINUX_ARCH_PATH=/home/kubu/buildroot/test/qemu_sparc64_sun4u_defconfig/build/linux-5.15/arch/sparc64
>
> But since LINUX_ARCH_PATH is not used for this architecture, it was not noticed.
>
> [1] https://git.buildroot.net/buildroot/tree/linux/linux.mk?h=2021.11#n226
>

Are you sure that this is a problem?
In the kernel Makefile, some 'ARCH' strings are treated specially:

# Additional ARCH settings for x86
ifeq ($(ARCH),i386)
        SRCARCH := x86
endif
ifeq ($(ARCH),x86_64)
        SRCARCH := x86
endif

# Additional ARCH settings for sparc
ifeq ($(ARCH),sparc32)
       SRCARCH := sparc
endif
ifeq ($(ARCH),sparc64)
       SRCARCH := sparc
endif

# Additional ARCH settings for parisc
ifeq ($(ARCH),parisc64)
       SRCARCH := parisc
endif


So compiling the kernel with ARCH=sparc64 is accepted, and the arch
directory will be arch/sparc . Similar to how compiling with
ARCH=x86_64 works even though arch/x86_64 does not (no longer) exist.

While I'm not familiar with sparc64, there does not seem to be a bug to me.

Thanks,
Thomas
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