linux-kernel - Re: [RFC PATCH 3/3] tools/nolibc: add a new "install_all

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Message-ID: <89a2e713-edfd-4556-b321-cdccc3437a43@t-8ch.de>
Date: Fri, 27 Jun 2025 07:11:45 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Arnd Bergmann <arnd@...db.de>
Cc: Willy Tarreau <w@....eu>, 
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>, linux-kernel@...r.kernel.org, 
	Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [RFC PATCH 3/3] tools/nolibc: add a new "install_all_archs"
 target

On 2025-06-26 23:15:07+0200, Arnd Bergmann wrote:
> On Thu, Jun 26, 2025, at 22:18, Thomas Weißschuh wrote:
> > On 2025-06-20 12:37:05+0200, Willy Tarreau wrote:
> >> This installs all supported archs together, both from nolibc and kernel
> >> headers. The arch-specific asm/ subdirs are renamed to asm-arch-$arch,
> >> and asm/ is rebuilt from all these files in order to include the right
> >> one depending on the build architecture.
> >> 
> >> This allows to use a single unified sysroot for all archs, and to only
> >> change the compiler or the target architecture. This way, a complete
> >> sysroot is much easier to use (a single directory is needed) and much
> >> smaller.
> >> 
> >> +	$(Q)rm -rf "$(OUTPUT)sysroot/include/asm"
> >> +	$(Q)mkdir -p "$(OUTPUT)sysroot/include/asm"
> >> +	@# Now install headers for all archs
> >> +	$(Q)for arch in $(patsubst aarch64,arm64,$(nolibc_supported_archs)); do \
> >> +		echo "# installing $$arch"; \
> >> +		if ! [ -d $(OUTPUT)sysroot/include/asm-arch-$$arch ]; then \
> >> +			$(MAKE) -C $(srctree) ARCH=$$arch mrproper; \
> >> +			$(MAKE) -C $(srctree) ARCH=$$arch headers_install no-export-headers= \
> >> +				INSTALL_HDR_PATH="$(OUTPUT)sysroot/include/$$arch" >/dev/null; \
> 
> >
> > I'm not a fan of the loop to build the ifdeffery. It is a duplication
> > of what we have in tools/include/nolibc/arch.h and horrible to look at.
> > Can we stick this into a reusable header file?
> > Something along the lines of this:
> >
> > 	/* asm/foo.h */
> > 	#define _NOLIBC_PER_ARCH_HEADER "foo.h"
> > 	#include "_nolibc_include_per_arch_header.h"
> >
> >
> > 	/* _nolibc_include_per_arch_header.h */
> > 	#if defined(__i386__)
> > 	#include CONCAT("asm-arch-x86/", _NOLIBC_PER_ARCH_HEADER)
> > 	#elif
> > 	...
> >
> > However, so far I couldn't get it to work.
> > Also it would be great if we can use it for the current arch.h, too.
> 
> I'm not sure either of those is better than the version we
> had until commit f3c8d4c7a728 ("kbuild: remove headers_{install,check}_all").
> which simply relied on a symlink to the architecture specific
> directory to be set.

Thanks for the pointer, that probably answers the question if this could
be part of kbuild proper. It shouldn't.

With the symlink, a given generic UAPI tree can be specialized to one
specific architecture. But here we want to create a full sysroot that works
for all architectures *at the same time*. So a symlink would not be enough.

> If it's indeed possible to concatenate the path name (I couldn't
> figure that out either), that could also be done in place of the
> symlink but simpler than the #if/#elif/#elif/... block, like
> 
> #include <arch.h> // defines ARCH_PREFIX
> #include CONCAT(ARCH_PREFIX, ioctl.h)

If we can't get it to work like this I would still prefer to have a
template header file which gets specialized with sed instead of the
Makefile loop.


Thomas