Please review blog post draft: powerpc64le-linux support

[Chris Marusich <cmmarusich@gmail.com>]

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Hi,

Léo and I have drafted the following blog post.  Could you take a few
minutes to read it and give us your thoughts?

It's a work in progress.  The primary goal is to announce the new
powerpc64le-linux support and explain why it matters (POWER9 is an
exciting, freedom-friendly platform!).  The secondary goal is to explain
some of the details about what we did, and invite people to get
involved.

Your feedback would be highly appreciated!

-- 
Chris

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From 8900d918106f6a70b20df461c5f086b5275773cc Mon Sep 17 00:00:00 2001
From: Chris Marusich <cmmarusich@gmail.com>
Date: Tue, 6 Apr 2021 00:10:35 -0700
Subject: [PATCH] website: drafts: Add powerpc64le-linux announcement.

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+title: powerpc64le-linux support in GNU Guix
+date: 2021-03-26 00:00
+author: Chris Marusich and Léo Le Bouter
+tags: porting, powerpc64le
+---
+
+It is a pleasure to announce that support for powerpc64le-linux
+(PowerISA v.2.07 and later) has now been
+[merged](https://issues.guix.gnu.org/47182) to the master branch of
+GNU Guix!
+
+This means that GNU Guix can be used immediately on this platform from
+a [from a Git
+checkout](https://guix.gnu.org/manual/en/html_node/Building-from-Git.html).
+Starting with the next release (Guix v1.2.1), you will also be able to
+[download a copy of Guix pre-built for
+powerpc64le-linux](https://guix.gnu.org/manual/en/guix.html#Binary-Installation).
+Regardless of how you get it, you can run the new powerpc64le-linux
+port of GNU Guix on top of any existing powerpc64le GNU/Linux
+distribution.
+
+This new platform is available as a "technology preview".  This means
+that although it is supported, substitutes are not yet available from
+the build farm, and some packages may fail to build.  Although
+powerpc64le-linux support is nascent, the Guix community is actively
+working on improving it, and this is a great time to [get
+involved](https://guix.gnu.org/manual/en/html_node/Contributing.html)!
+
+### Why Is This Important?
+
+This is important because it means that GNU Guix now works on the [RYF
+Talos II and Talos II Lite
+mainboards](https://www.fsf.org/news/talos-ii-mainboard-and-talos-ii-lite-mainboard-now-fsf-certified-to-respect-your-freedom)
+and it's IBM POWER9 processor.  This is a modern, performant hardware
+platform that respects your freedom.  It can run without any non-free
+code, all the way down to its bootloader and firmware.  It's a
+freedom-friendly platform that aligns well with GNU Guix's commitment
+to software freedom.
+
+How is this any different from existing RYF hardware, you might ask?
+The existing RYF
+[laptops](https://ryf.fsf.org/products?category=1&vendor=All&sort_by=created&sort_order=DESC),
+[mainboards](https://ryf.fsf.org/products?category=5&vendor=All&sort_by=created&sort_order=DESC),
+and
+[workstations](https://ryf.fsf.org/products?category=30&vendor=All&sort_by=created&sort_order=DESC)
+can only really be used with Intel Core Duo or AMD Opteron processors.
+Those processors were released over 15 years ago.  Since then,
+processor performance has increased drastically.  People should not
+have to choose between performance and freedom, but the fact is that
+for many years, that is exactly what we were forced to do.  However,
+the Talos II and Talos II Lite have changed this: the free software
+community now has an RYF-certified option that can compete with the
+performance of modern Intel and AMD systems.
+
+Although the performance of POWER9 processors is competitive with
+modern Intel and AMD processors, its real advantage is that it<
+respects your freedom.  Modern processors from [both Intel and AMD
+include back
+doors](https://www.fsf.org/blogs/sysadmin/the-management-engine-an-attack-on-computer-users-freedom)
+over which you are given no control.  Additionally, hardware design
+defects in the processors of both vendors have been discovered, giving
+rise to critical security vulnerabilities like
+[Spectre](https://en.wikipedia.org/wiki/Spectre_(security_vulnerability))
+and
+[Meltdown](https://en.wikipedia.org/wiki/Meltdown_(security_vulnerability)).
+In many cases, these vulnerabilities can only be fixed by installing
+[non-free CPU microcode](https://wiki.debian.org/Microcode) - unless,
+of course, [the vendor decides not to provide any fix at
+all](https://arstechnica.com/gadgets/2018/04/intel-drops-plans-to-develop-spectre-microcode-for-ancient-chips/)!
+
+Compared to that, the RYF Talos II and Talos II Lite are a breath of
+fresh air that the free software community really deserves.  Raptor
+Computing Systems' commitment to software freedom and owner control is
+an inspiring reminder that it **is** possible to ship a great product
+that respects the freedom of your customers.  And going forward, the
+future looks bright for the open, royalty-free Power ISA, [which is
+now a Linux Foundation
+project](https://www.linuxfoundation.org/press-release/2019/08/the-linux-foundation-announces-new-open-hardware-technologies-and-collaboration/)
+(see also: [the same announcement from The OpenPOWER
+Foundation](https://openpowerfoundation.org/the-next-step-in-the-openpower-foundation-journey/).
+
+### About other freedom-friendly platforms
+
+The authors believe that the Power ISA, in particular the RYF Talos II
+from Raptor Computing Systems, is a good, freedom-friendly choice for
+a server or a desktop workstation.  If we didn't, we wouldn't be
+writing this blog post!  However, it is worth noting that other
+freedom-friendly platforms exist, too.  For example, RISC-V is another
+platform that is quite interesting from a freedom standpoint.
+
+In the opinion of these authors, any platform that furthers the cause
+of software freedom is a good platform.  For this reason, we want to
+make it clear that we do not consider freedom-friendly platforms like
+Power ISA or RISC-V (or others) to be in competition with one another.
+All people deserve freedom, thus all people deserve a computing
+platform that respects their freedom.  It doesn't matter if it's Power
+ISA, RISC-V, or something else; if it suits your needs and respects
+your freedom, it's good, and we want more of it!
+
+On that topic, Guix still needs a RISC-V port.  Perhaps you (yes, you,
+the RISC-V fan reading this right now!) could be the one to start the
+porting work for that platform?  The Guix community is very friendly,
+so [come and join us](https://guix.gnu.org/en/contribute/), and let's
+build it together!
+
+### Bootstrapping powerpc64le-linux: A Journey
+
+To build software, you need software.  How can one port Guix to a
+platform before support for that platform exists?  This is a
+[bootstrapping
+problem](https://guix.gnu.org/manual/en/html_node/Bootstrapping.html).
+
+In Guix, all software for a given system (e.g., powerpc64le-linux) is
+built starting from its bootstrap binaries.  It is intended that the
+bootstrap binaries are the only pieces of software in the entire
+package collection that Guix cannot build from source.  In practice,
+[additional bootstrap roots are
+possible](https://lists.gnu.org/archive/html/guix-devel/2015-02/msg00814.html),
+but introducing them in Guix is highly discouraged, and our community
+[actively](https://guix.gnu.org/en/blog/2019/guix-reduces-bootstrap-seed-by-50/)
+[works](https://guix.gnu.org/en/blog/2020/guix-further-reduces-bootstrap-seed-to-25/)
+to [reduce](https://guix.gnu.org/en/blog/2018/bootstrapping-rust/) our
+overall bootstrap footprint.
+
+So first you need to build the the bootstrap binaries for your
+platform.  In theory, you can do this in many ways.  For example, you
+might try to manually compile them on an existing system.  However,
+Guix has [package
+definitions](https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/packages/make-bootstrap.scm?id=5d8c2c00d60196c46a32b68c618ccbe2b3aa48f4)
+that you can use to build them - using Guix, of course!
+
+Commonly, the first step in [porting Guix to a new
+platform](https://guix.gnu.org/manual/en/html_node/Porting.html) is to
+use Guix to cross-compile the bootstrap binaries for that new platform
+from a platform on which Guix is already supported. This can be done
+by running a command like the following on a system where Guix is
+already installed:
+
+```scheme
+guix build --target=powerpc64le-linux-gnu bootstrap-tarballs
+```
+
+This is the route that we took when building the powerpc64le-linux
+bootstrap binaries, as described in commit
+[8a1118a](https://git.savannah.gnu.org/cgit/guix.git/commit/?id=8a1118a96c9ae128302c3d435ae77cb3dd693aea).
+
+Note that before you can even do this, you must first update the
+glibc-dynamic-linker and system->linux-architecture procedures in
+Guix's code, as described in
+[Porting](https://guix.gnu.org/manual/en/html_node/Porting.html).  In
+addition, the versions of packages in Guix that make up the GNU
+toolchain (gcc, glibc, etc.) must already support the target platform.
+This pre-existing toolchain support needs to be good enough so that
+Guix can (1) build, on some already-supported platform, a
+cross-compilation toolchain for that target, (2) use, on that same
+platform, the cross-compilation toolchain to cross-compile the
+bootstrap binaries for the target platform, and (3) use, on the target
+platform, the bootstrap binaries to natively build the rest of the
+Guix package collection.  The above "guix build" command takes care of
+steps (1) and (2) automatically.
+
+Step (3) is a little more involved.  Once the bootstrap binaries for
+the target platform have been built, they must be made available for
+anyone to download.  In addition, Guix's code must be updated so that
+(a) it recognizes the system (e.g., "powerpc64le-linux") that will be
+used to identify the new platform and (b) it fetches the new system's
+bootstrap binaries from the right location.  Commit
+[8a1118a](https://git.savannah.gnu.org/cgit/guix.git/commit/?id=8a1118a96c9ae128302c3d435ae77cb3dd693aea)
+accomplishes both of those things.  After that, you just have to try
+building things and see what breaks, for example by running
+`./pre-inst-env guix build hello` from your Git checkout to build GNU
+Hello.
+
+The actual bootstrap binaries for powerpc64le-linux are stored on the
+[alpha.gnu.org FTP
+server](https://alpha.gnu.org/gnu/guix/bootstrap/powerpc64le-linux/20210106/).
+Chris Marusich built these bootstrap binaries in an x86_64-linux Guix
+System VM which was running on hardware owned by Léo Le Bouter.  Chris
+then signed the binaries and provided them to Ludovic Courtès, who in
+turn verified their authenticity, signed them, and [uploaded them to
+alpha.gnu.org](https://debbugs.gnu.org/cgi/bugreport.cgi?bug=41669#125).
+
+With the bootstrap binaries finally in place, we could get started on
+step (3) above: building the rest of the package collection.  Or
+trying to, at least.  There were many stumbling blocks.  For example,
+to resolve some test failures, we had to update the code in Guix that
+allows it to make
+[certain](https://git.savannah.gnu.org/cgit/guix.git/commit/?id=b57de27d0331198c9cafb09a1cf8a5fa4f691e36)
+[syscalls](https://git.savannah.gnu.org/cgit/guix.git/commit/?id=c29bfbfc78ccd9e5c10d38faf3d269eafed12854)
+from scheme.  As another example, we had to [patch GCC so that it
+looks for the 64-bit libraries in
+/lib](https://debbugs.gnu.org/cgi/bugreport.cgi?bug=46253), rather
+than /lib64, since that is where Guix puts its 64-bit libraries by
+convention.  Some packages required for Guix failed to build, so we
+had to debug those build failures, too.
+
+For a list of all the changes, see [the patch
+series](https://debbugs.gnu.org/cgi/bugreport.cgi?bug=47182) or the
+actual commits, which are:
+
+```
+$ git log --oneline --no-decorate 8a1118a96c9ae128302c3d435ae77cb3dd693aea..65c46e79e0495fe4d32f6f2725d7233fff10fd70
+65c46e79e04 gnu: sed: Make it build on SELinux-enabled kernels.
+93f21e1a35e utils: Fix target-64bit? on powerpc64le-linux.
+8d9aece8c49 ci: %cross-targets: Add powerpc64le-linux-gnu.
+c29bfbfc78c syscalls: Fix RNDADDTOENTCNT on powerpc64le-linux.
+b57de27d033 syscalls: Fix clone on powerpc64le-linux.
+a16eb6c5f97 Add powerpc64le-linux as a supported Guix architecture.
+b50f4268035 gnu: libelf: Fix compilation for powerpc64le-linux.
+1a0f4013d33 gnu: texlive-latex-base: Fix compilation on powerpc64le*.
+e9938dc8f0e gnu: texlive-bin: Fix compilation on powerpc64le*.
+69b3907adf6 gnu: guile-avahi: Fix compilation on powerpc64le-linux.
+4cc2d2aa599 gnu: bdb-4.8: Fix configure on powerpc64le-linux.
+be4b1cf53bd gnu: binutils-final: Support more Power architectures.
+060478c32c9 gnu: binutils-final: Provide bash for binary on powerpc-linux.
+b2135b5d576 gnu: gcc-boot0: Enable 128-bit long double for POWER9.
+6e98e9ca923 gnu: glibc: Fix ldd path on powerpc*.
+cac88b28b83 gnu: gcc-4.7: On powerpc64le, fix /lib64 references.
+fc7cf0c1ecc utils: Add target-powerpc? procedure.
+```
+
+In the end, through the combined efforts of multiple people, we slowly
+worked through the issues until we reached a point where we could do
+all of the following things successfully:
+
+- Build Guix manually on a [Debian GNU/Linux
+  ppc64el](https://wiki.debian.org/ppc64el) machine (yet another name
+  for the powerpc64le-linux-gnu triplet), and all of its "make check"
+  tests passed.
+- Build GNU Hello using Guix and run it.
+- Run "guix pull" to build and install the most recent version of
+  Guix, with powerpc64le-linux support.
+- Build a release binary tarball for powerpc64le-linux using "make
+  guix-binary.powerpc64le-linux.tar.xz"
+- Use that binary to install a version of Guix that could build/run
+  GNU Hello and run "guix pull" successfully.
+
+This was an exciting moment!  But there was still more work to be
+done.
+
+Originally, we did this work on the wip-ppc64le branch, with the
+intent of merging it into core-updates.  By convention, the
+"[core-updates](https://guix.gnu.org/manual/en/html_node/Submitting-Patches.html)"
+branch in Guix is where changes are made if they cause too many
+rebuilds.  Since we were updating package definitions so deep in the
+dependency graph of the package collection, we assumed it wouldn't be
+possible to avoid rebuilding the world.  For this reason, we had based
+the wip-ppc64le branch on core-updates.
+
+However, Efraim Flashner proved us wrong!  He created a separate
+branch, wip-ppc64le-for-master, where he adjusted some of the
+wip-ppc64le commits to avoid rebuilding the world on other platforms.
+Thanks to his work, we were able to merge the changes directly to
+master!  This meant that we would be able to include it in the next
+release (Guix v.1.2.1).
+
+In short, the initial porting work is done, and it is now possible for
+anyone to easily try out Guix on this new platform.  Because "guix
+pull" works, too, it is also easy to iterate on what we have and work
+towards improving support for the platform.  It took a lot of
+cooperation and effort to get this far, but there are multiple people
+actively contributing to this port in the Guix community who want to
+see it succeed, and we hope you will join us in exploring the limits
+of this exciting new freedom-friendly platform!
+
+
+### Hiccups Along the Way
+
+Along the way, there were a few problems that stymied our porting
+attempts.
+
+First, we thought we would try to port to powerpc64-linux
+(big-endian).  This did not prove to be any easier than the
+little-endian port.  In addition, other distributions (e.g.,
+[Debian](https://www.debian.org/ports/) and
+[Fedora](https://fedoraproject.org/wiki/Architectures)) have recently
+dropped their big-endian powerpc64 ports, so the little-endian variant
+is more likely to be tested and supported in the community.  So we
+decided to focus our efforts on the little-endian variant, and so far
+we haven't looked back.
+
+In both the big-endian and little-endian case, we were saddened to
+discover that the bootstrap binaries are not entirely reproducible.
+This fact is documented in [bug
+41669](https://debbugs.gnu.org/cgi/bugreport.cgi?bug=41669), along
+with our extensive investigations.  In short, if you build the
+bootstrap binaries on two separate machines without using any
+substitutes, you will find that the derivation which cross-compiles
+%gcc-static (the bootstrap GCC, version 5.5.0) produces different
+output on the two systems.  However, if you build %gcc-static twice on
+the same system, it builds reproducibly.  This suggests that something
+in the transitive closure of inputs of %gcc-static is perhaps
+contributing to its non-reproducibility.  There is an interesting graph toward the end of the bug report that suggests that the non-reproducibliity is introduced by one or more of 21 derivations in the transitive closure of %gcc-static's inputs that do not build reproducibly across systems.
+
+At some point, you have to cut your losses and move on.  After months
+of investigation without resolving the reproducibility issue, we
+finally decided to move forward with the bootstrap binaries produced
+earlier.  If necessary, we can always go back and try to fix this
+issue, but it seemed more important to get started with the
+bootstrapping work.  Anyone who is interested in solving this problem
+can comment on the bug report and help us figure out the mystery.  We
+are very interested in solving it, but at the moment we are more
+interested in bootstrapping the rest of the system with the existing
+bootstrap binaries.
+
+### Next Steps
+
+It is now possible to install Guix on a powerpc64le-linux system and
+use it to build some useful software - in particular, Guix itself.  So
+Guix is now "self-hosted" on this platform, which gives us a
+comfortable place to begin further work.
+
+The following tasks still need to be done.  Anyone can help, so please
+get in touch if you want to contribute!
+
+- Solve the GCC bootstrap binary reproducibility issue.
+- Get Guix System to work on powerpc64le-linux.
+- Get CI infrastructure to work (Cuirass, guix-build-coordinator,
+  substitutes, etc.)
+- Fix all package build failures.
+- Try building rust, and if it works, judiciously re-introduce the
+  librsvg dependency for powerpc64le-linux in gtk+ and gtk+-2, since
+  [it is currently
+  missing](https://git.savannah.gnu.org/cgit/guix.git).
+- Upgrade GCC to 8 on core-updates, fix issues that occur.
+- Merge core-updates to master after that.
-- 
2.30.2


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