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Armando Faz edited this page Jun 6, 2025 · 1 revision

Bazel Compilation

Use this repository for a minimal reproducible example:

https://github.com/armfazh/circl-bazel-adventure

To compile and run our Go application, just type:

bazel run //:circl-bazel-adventure

You should see random keys printed to the console!

Compilation Issue Solved! 🧩

In Issue #537, it was reported that CIRCL failed to build with Bazel.

TL;DR Update rules_go to v0.55.0

Thanks to @patrickmscott who work on the solution PR #4298.

Detailed Explanation

The rules_go is the official Bazel extension that teaches Bazel how to build and test Go programs. It provides the essential rules—like go_binary, go_library, and go_test—that translate your Go source code into targets Bazel can understand, compile, and manage.

The issue was that rules_go was not properly including header files used in CIRCL.

In Go, there exist two types of headers (i.e., files with .h extension):

  • C Headers - Used for including C code (when compling with CGO=1 support).
  • Assembler Headers - Used in assembler files to include definitions and macros. These files are not related to C nor CGO support.

CIRCL is a heavy-optimized library that uses assembler routines and relies a lot in assembler headers.

To compound the complexity of the problem, it is also possible to include assembler headers inside of another assembler header (even if it is defined in a different package of the same project).

Issue

To reproduce the issue, set rules_go version to <=0.54.0.

- bazel_dep(name = "rules_go", version = "")
+ bazel_dep(name = "rules_go", version = "0.54.0")

The output looks like this

$ bazel run //:circl-bazel-adventure

Use --sandbox_debug to see verbose messages from the sandbox and retain the
sandbox build root for debugging
external/gazelle++go_deps+com_github_cloudflare_circl/dh/x25519/curve_amd64.s:8:
#include:
open external/gazelle++go_deps+com_github_cloudflare_circl/math/fp25519/fp_amd64.h: no such file or directory

The error points to the abscense of the assembler header file fp_amd64.h (which includes prime field arithmetic for the AMD64 architecture).

Several hacks were suggested in the meantime.

Solution

Update rules_go version to 0.55.0.

- bazel_dep(name = "rules_go", version = "0.54.0")
+ bazel_dep(name = "rules_go", version = "0.55.0")

and compilation just works.

The BUILD.bazel File: A Closer Look 👀

So, what's going on in that BUILD.bazel file? Let's break it down.

load("@rules_go//go:def.bzl", "go_binary", "go_library")

go_library(
    name = "circl-bazel-adventure_lib",
    srcs = ["main.go"],
    importpath = "github.com/user/circl-bazel-adventure",
    visibility = ["//visibility:private"],
    deps = ["@com_github_cloudflare_circl//dh/x25519:go_default_library"],
)

go_binary(
    name = "circl-bazel-adventure",
    embed = [":circl-bazel-adventure_lib"],
    visibility = ["//visibility:public"],
)
  • load(...): This line imports the Go rules we need from the Bazel Go rules library. These are the building blocks for our Go project.
  • go_library(...): This rule defines a Go library. We've named it go-bazel-adventure_lib and told it that our source code is in main.go. Think of this as compiling the reusable parts of our code.
  • go_binary(...): This rule creates the final executable program. We've named it go-bazel-adventure and told it to "embed" or include our go-bazel-adventure_lib.

And that's the core of it! You define your code and its dependencies, and Bazel figures out the rest.

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