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+---
+layout: post
+title:  "The Case for Using Guix to Solve the gem5 Packaging Problem"
+author: Christopher Batten<sup>1</sup>, Pjotr Prins<sup>2</sup>, Efraim Flashner<sup>2</sup>, Arun Isaac<sup>2</sup>,Ekaiz Zarraga<sup>2</sup>, Erik Garrison<sup>2</sup>, Tuan Ta<sup>1</sup>
+date:   2022-05-23
+categories: project
+---
+
+<sup>1</sup> School of Electrical and Computer Engineering, Cornell University, Ithaca, NY <br>
+<sup>2</sup> The University of Tennessee Health Science Center, Memphis, TN <br>
+<sup>3</sup> ElenQ Technology
+
+This post will first describe the gem5 packaging problem before making
+the case for using Guix, a mature functional cross-platform package
+manager, for building, distributing, installing, and managing the gem5
+ecosystem.
+
+The gem5 Packaging Problem
+--------------------------------------------------------------------------
+
+The gem5 simulator has become the defacto standard for cycle-level
+simulation, and gem5 now supports evaluating a diverse set of workloads.
+Unfortunately, both the gem5 simulator and gem5 workloads still lack a
+compelling software packaging solution to simplify building,
+distributing, installing, and managing the gem5 ecosystem. In this
+section, we describe the gem5 simulator and workload packaging problems
+before sketching an ideal software packaging solution.
+
+**The gem5 Simulator Packaging Problem --** The gem5 simulator is a
+complex piece of software with numerous build- and run-time dependencies
+including a modern C++ compiler, SCons, Boost, and Python. To mitigate
+dependency issues, the gem5 installation instructions strongly recommend
+using specific versions of Ubuntu. The gem5 simulator has numerous
+compile-time options to experiment with different ISAs, coherence
+protocols, and/or accelerators, and this in turn makes providing a single
+precompiled binary difficult. Even so, the gem5 community does point new
+researchers to a small number of precompiled Docker images. Given these
+challenges, the gem5 community has chosen not to support any kind of
+packaging for the gem5 simulator. Almost all researchers individually
+manage dependencies and recompile the gem5 simulator from source.
+
+**The gem5 Workload Packaging Problem --** Building workloads to run on
+the gem5 simulator using syscall emulation can be just as challenging as
+building the gem5 simulator itself. These workloads must be
+cross-compiled meaning researchers must build a complete
+cross-compilation toolchain for each target architecture. Researchers
+might also need to build an emulator (e.g., QEMU) to test these workloads
+before moving to cycle-level simulation. Researchers must ensure the
+workloads only use static libraries and do not call any unsupported
+syscalls. Given these challenges, the gem5 community directly included
+precompiled binaries as part of the gem5 source distribution for many
+years. More recently, the community has migrated to pre-compiled binaries
+as part of the gem5 resources project.
+
+An ideal software packaging solution would be: _reproducible --_ easily
+duplicate precisely specified development environments; _transparent --_
+understand entire development environment including exact build
+configuration and version of every dependency; _composable --_ easily
+integrate the gem5 simulator and workload into standard development
+environments without needing cumbersome, heavyweight containers; _fast --_
+leverage precompiled packages; _distribution agnostic --_ enable
+researchers to use the Linux distribution of their choice; _unified --_
+same packaging solution can be used for both the gem5 simulator and
+workloads; _portable --_ easily build gem5 workloads for native execution
+and/or target multiple ISAs for cycle-level simulation without manually
+managing multiple cross-compilation toolchains; and _flexible --_ easily
+switch between development environments, modify existing packages, add
+new packages, produce reproducible workflows, and/or generate containers.
+
+## Using Guix for gem5
+
+Guix is a mature functional cross-platform package manager with hundreds
+of committers and over 20K packages. In this section, we briefly describe
+our on-going efforts to use Guix for packaging both the gem5 simulator
+and gem5 workloads.
+
+**Using Guix to Package gem5 Simulators --** We have developed a
+proof-of-concept Guix package for the gem5 simulator that handles all
+build- and run-time dependencies and installation[^1]. The package builds
+gem5 for six ISAs, ensures builds are reproducible by eliminating
+non-deterministic use of `|__DATE__|` and `|__TIME__|`, patches the build
+environment to work with SCons, and performs a well-structured install of
+the gem5 simulator binaries and example configurations. The package is:
+_reproducible_ through the use of isolated and deterministic
+environments for experimenting with the gem5 simulator; _transparent_,
+since the complete recursive dependency graph is precisely specified;
+_composable_, since the gem5 simulator is installed just like any
+other tool without the need for a container; and _distribution
+agnostic_, since the package can be installed on Ubuntu, RHEL, SUSE, or
+even Guix System which is an entire distribution based exclusively on
+Guix. Derived packages could enable easily providing packages for
+different compile-time configurations. When merged upstream into the main
+Guix package repository, this package will be part of the Guix build farm
+enabling binary package substitution for _fast_ installation.
+
+**Using Guix to Package gem5 Workloads --** Guix already includes
+packages for QEMU and cross-compilation toolchains for commercial ISAs.
+We are contributing to the RISC-V port of Guix including packaging the
+RISC-V cross-compilation toolchain. We identified a simple Smith-Waterman
+sequence alignment Guix package as an interesting gem5 workload and
+developed a derived Guix package that patches the standard build process
+to produce a statically linked binary[^2]. In addition to being
+_reproducible_, _transparent_, _composable_, and _distribution agnostic_,
+using Guix is also _portable_, since we can easily cross-compile the
+package for ARM or RISC-V, and _flexible_, since it requires only eight
+lines of Guile code to create a new derived package supporting static
+compilation.
+
+## Case Study
+
+The attached appendix describes step-by-step commands for a case study
+that: installs QEMU, gem5, and cross-compilers for x86, ARM, and RISC-V
+in an isolated environment; cross-compiles and runs Smith-Waterman for
+all three ISAs; and runs this benchmark on the in-order and out-of-order
+timing models. To reproduce this case study, a researcher first must
+download and install Guix[^3].
+
+### Add new channel
+
+By default, Guix includes its own main package repository, but users can
+also create their own ``channels'' that include third-party packages. We
+need to add such a channel to get access to the gem5 simulator package
+and the derived Smith-Waterman package.
+
+     % cd $HOME/.config/guix
+     % cat > channels.scm \
+    <<'END'
+    (use-modules (guix ci))
+    (list
+     (channel
+      (name 'gn-bioinformatics)
+      (url (string-append "https://git.genenetwork.org/"
+             "guix-bioinformatics/guix-bioinformatics.git"))
+      (branch "master"))
+     (channel-with-substitutes-available
+      %default-guix-channel "https://ci.guix.gnu.org"))
+    END
+
+### Update Guix and install Smith-Waterman
+
+We use `guix pull` to download all of the package descriptions from the
+main package repository along with any third-party packages. We then
+install the default Smith-Waterman package and run it natively. Here we
+use the default "profile", but we could also install this package in a
+dedicated Guix "profile", similar to Python's virtual environment.
+
+    % mkdir -p $HOME/tmp/misc/test-guix
+    % cd $HOME/tmp/misc/test-guix
+    % guix pull
+    % guix install smithwaterman
+    % smithwaterman -p TGATTGTACCAAA TGATCATGTACCA
+
+### Install QEMU and gem5
+
+We now install both the QEMU and gem5 packages for all architectures in
+the same profile.
+
+    % guix install qemu
+    % guix install gem5
+
+### Build and run Smith-Waterman for x86_64 ISA
+
+We use `guix build --target=x86_64-linux-gnu` to cross-compile
+most Guix packages for x86_64. Here we cross-compile the derived package
+for Smith-Waterman which produces a statically linked executable that we
+then run on both QEMU and gem5.
+
+    % cd $HOME/tmp/misc/test-guix
+    % DIR=$(guix build \
+             --target=x86_64-linux-gnu smithwaterman-static)
+    % ln -sf $DIR/bin/smithwaterman sw-x86_64
+    % qemu-x86_64 ./sw-x86_64 -p TGATTGTACCAAA TGATCATGTACCA
+    % gem5-x86.opt \
+        $GUIX_PROFILE/share/gem5/configs/example/se.py \
+        --cmd=./sw-x86_64 \
+        --options="-p TGATTGTACCAAA TGATCATGTACCA"
+
+### Build and run Smith-Waterman for ARM ISA
+
+We use `guix build --target=aarch64-linux-gnu` to cross-compile
+most Guix packages for ARM. Here we cross-compile the derived package for
+Smith-Waterman which produces a statically linked executable that we then
+run on both QEMU and gem5.
+
+    % cd $HOME/tmp/misc/test-guix
+    % DIR=$(guix build \
+             --target=aarch64-linux-gnu smithwaterman-static)
+    % ln -sf $DIR/bin/smithwaterman sw-aarch64
+    % qemu-aarch64 ./sw-aarch64 -p TGATTGTACCAAA TGATCATGTACCA
+    % gem5-arm.opt \
+        $GUIX_PROFILE/share/gem5/configs/example/se.py \
+        --cmd=./sw-aarch64 \
+        --options="-p TGATTGTACCAAA TGATCATGTACCA"
+
+### Build and run Smith-Waterman for RISC-V ISA
+
+We use `guix build --target=riscv64-linux-gnu` to cross-compile
+most Guix packages for RISC-V. Here we cross-compile the derived package for
+Smith-Waterman which produces a statically linked executable that we then
+run on both QEMU and gem5.
+
+    % cd $HOME/tmp/misc/test-guix
+    % DIR=$(guix build \
+             --target=riscv64-linux-gnu smithwaterman-static)
+    % ln -sf $DIR/bin/smithwaterman sw-riscv64
+    % qemu-riscv64 ./sw-riscv64 -p TGATTGTACCAAA TGATCATGTACCA
+    % gem5-riscv.opt \
+        $GUIX_PROFILE/share/gem5/configs/example/se.py \
+        --cmd=./sw-riscv64 \
+        --options="-p TGATTGTACCAAA TGATCATGTACCA"
+
+### Run experiment on RISC-V ISA
+
+Once we have used Guix to install the gem5 simulator and the gem5
+workload packages, we can easily perform a computer architecture research
+experiment. Here we compare the performance of running Smith-Waterman on
+an in-order vs.~out-of-order RISC-V processor model.
+
+    % cd $HOME/tmp/misc/test-guix
+
+    % gem5-riscv.opt \
+        --outdir=m5out-minor-sw \
+        $GUIX_PROFILE/share/gem5/configs/example/se.py \
+        --cmd=./sw-riscv64 \
+        --options="-p TGATTGTACCAAA TGATCATGTACCA" \
+        --cpu-type=MinorCPU --ruby
+
+    % gem5-riscv.opt \
+        --outdir=m5out-o3-sw \
+        $GUIX_PROFILE/share/gem5/configs/example/se.py \
+        --cmd=./sw-riscv64 \
+        --options="-p TGATTGTACCAAA TGATCATGTACCA" \
+        --cpu-type=O3CPU --ruby
+
+    % grep system.cpu.numCycles m5out-minor-sw/stats.txt
+    % grep system.cpu.numCycles m5out-o3-sw/stats.txt
+
+Acknowledgements
+--------------------------------------------------------------------------
+
+This work was supported by NSF PPoSS Award #2118709 and NLNet awards for
+GNUMes-RISCV and Guix-Riscv64.
+
+[^1]: <https://git.genenetwork.org/guix-bioinformatics/guix-bioinformatics/src/branch/master/gn/packages/virtualization.scm>
+[^2]: <https://git.genenetwork.org/guix-bioinformatics/guix-bioinformatics/src/branch/master/gn/packages/static.scm>
+[^3]: <https://guix.gnu.org/en/download>
+