Ken's comments
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@ -47,8 +47,8 @@ TLDR:
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Uber started in 2010, has clocked over 15 billion trips, and made lots of cool
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and innovative tech for it to happen. General-purpose "allowed" server-side
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languages are Go and Java, with Python and Node allowed for specific use cases
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(like front-end for Node and Python for data analysis/ML). Use of other
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languages in back-end code is minimal.
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(like front-end for Node and Python for data analysis/ML). C++ is used for a few
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low level libraries. Use of other languages in back-end code is minimal.
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Our Go Monorepo is larger than Linux kernel[^1], and worked on by a couple of
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thousand engineers. In short, it's big.
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@ -83,7 +83,8 @@ wave --- I still remember the complexity.
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At the time, the Go monorepo already used a hermetic Go toolchain. Therefore,
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the Go compiler used to build the monorepo was unaffected by the compiler
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installed on the system, if any. Therefore, on whichever environment a Go build
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was running, it always used the same version of Go.
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was running, it always used the same version of Go. Bazel docs [explain this
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better than me][bazel-hermetic].
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{{<img src="_/2022/uber-zig-gm-221.png"
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alt="A Jira task asking for a hermetic C++ toolchain."
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@ -96,7 +97,7 @@ unavoidable for some our Go code to use [CGo][cgo], so it needs a C/C++
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compiler. Go then links the Go and C parts to the final executable.
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The C++ toolchain was not hermetic since the start of Go monorepo: Bazel would
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use whatever it found on the system. That meant clang on macOS, gcc (whatever
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use whatever it found on the system. That meant Clang on macOS, GCC (whatever
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version) on Linux. Setting up a hermetic C++ toolchain in Bazel is a lot of
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work (think person-months for our monorepo), there was no immediate need, and
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it also was not painful *enough* to be picked up.
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@ -122,11 +123,12 @@ All of these issues were annoying, but not enough to invest into the toolchain.
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### 2020 Dec: need musl
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I was working on a toy project that is built with Bazel and uses CGo. I wanted
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my binary to be static, but Bazel does not make that easy. I spent a couple of
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evenings creating a Bazel toolchain on top of [musl.cc](https://musl.cc), but
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didn't go far, because at the time I wasn't able to make sense out of the
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Bazel's toolchain documentation, and I didn't find a good example to rely on.
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I was working on a non-Uber-related toy project that is built with Bazel and
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uses CGo. I wanted my binary to be static, but Bazel does not make that easy. I
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spent a couple of evenings creating a Bazel toolchain on top of
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[musl.cc](https://musl.cc), but didn't go far, because at the time I wasn't
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able to make sense out of the Bazel's toolchain documentation, and I didn't
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find a good example to rely on.
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### 2021 Jan: discovering `zig cc`
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@ -137,12 +139,13 @@ understand the remaining article better, because I gave the talk to a Zig
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audience). To sum up the Andrew's article, `zig cc` has the following
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advantages:
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- Fully hermetic C/C++ compiler in ~40MB tarball.
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- Fully hermetic C/C++ compiler in ~40MB tarball. This is an order of magnitude
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smaller than the standard Clang distributions.
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- Can link against a glibc version that was provided as a command-line argument
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(e.g. `-target x86_64-linux-gnu.2.28` will compile for x86_64 Linux and link
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against glibc 2.28).
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- Host and target are decoupled. The setup is the same for both linux-aarch64
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and darwin-x86_64 targets, regardless of the host.
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- Host and target are decoupled. The setup is the same for both `linux-aarch64`
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and `darwin-x86_64` targets, regardless of the host.
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- Linking with musl is "just a different libc version": `-target
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x86_64-linux-musl`.
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@ -201,7 +204,7 @@ dependency on system libraries and undoing of a lot of technical debt.
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justification.
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- bazel-zig-cc kinda works, but both bazel-zig-cc and zig cc have known bugs.
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- I can't realistically implement the necessary changes or bug fixes. I tried
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implementing `zig ar`, a trivial front-end for llvm's `ar`, and failed.
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implementing `zig ar`, a trivial front-end for LLVM's `ar`, and failed.
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- Once an issue had been identified as a Zig issue, getting attention from Zig
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developers was unpredictable. Some issues got resolved within days, some took
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more than 6 months, and donations din't change `zig cc` priorities.
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@ -232,7 +235,7 @@ research on this unproven prototype.
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Given that we now needed a cross-compiler, we had two candidates:
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- [grailbio/bazel-toolchain][grailbio/bazel-toolchain]. Uses a vanilla clang.
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- [grailbio/bazel-toolchain][grailbio/bazel-toolchain]. Uses a vanilla Clang.
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No risk. Well understood. Obviously safe and correct solution.
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- [~motiejus/bazel-zig-cc][bazel-zig-cc]: uses `zig cc`. Buggy, risky, unsafe,
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uncertain, used-by-nobody, but quite a tempting solution.
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@ -366,3 +369,4 @@ Many thanks Abhinav Gupta and Loris Cro for reading drafts of this.
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[milan-youtube]: https://www.youtube.com/watch?v=SCj2J3HcEfc
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[zig-motiejus-issues]: https://github.com/ziglang/zig/issues?q=author%3Amotiejus+sort%3Acreated-asc
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[kmicklas]: https://github.com/kmicklas
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[bazel-hermetic]: https://bazel.build/concepts/hermeticity
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