question: how to fix bazel errors when cross-compiling for arm64?

[errordeveloper]

There had been a few issue regarding arm64 (#10512, #7686 & #1861), but this one is not a feature request.
I have attempted to configure Bazel to cross-compile for arm64, but I am facing a roadblock.

Here is what I did:

• read Bazel docs (Configuring C++ toolchains)
• implemented the changes and pushed to a branch errordeveloper@6496fdd

When I test my changes, I get this:

$ bazel build --config=cross_aarch64  //source/exe:envoy-static
INFO: Build options --cpu, --crosstool_top, and --host_crosstool_top have changed, discarding analysis cache.
ERROR: /root/.cache/bazel/_bazel_root/f8087e59fd95af1ae29e8fcb7ff1a3dc/external/envoy/bazel/foreign_cc/BUILD:40:1: in configure_make rule @envoy//bazel/foreign_cc:luajit: 
Traceback (most recent call last):
	File "/root/.cache/bazel/_bazel_root/f8087e59fd95af1ae29e8fcb7ff1a3dc/external/envoy/bazel/foreign_cc/BUILD", line 40
		configure_make(name = 'luajit')
	File "/root/.cache/bazel/_bazel_root/f8087e59fd95af1ae29e8fcb7ff1a3dc/external/rules_foreign_cc/tools/build_defs/configure.bzl", line 29, in _configure_make
		cc_external_rule_impl(ctx, <1 more arguments>)
	File "/root/.cache/bazel/_bazel_root/f8087e59fd95af1ae29e8fcb7ff1a3dc/external/rules_foreign_cc/tools/build_defs/framework.bzl", line 252, in cc_external_rule_impl
		attrs.create_configure_script(<1 more arguments>)
	File "/root/.cache/bazel/_bazel_root/f8087e59fd95af1ae29e8fcb7ff1a3dc/external/rules_foreign_cc/tools/build_defs/configure.bzl", line 43, in attrs.create_configure_script
		create_configure_script(<12 more arguments>)
	File "/root/.cache/bazel/_bazel_root/f8087e59fd95af1ae29e8fcb7ff1a3dc/external/rules_foreign_cc/tools/build_defs/configure_script.bzl", line 17, in create_configure_script
		get_env_vars(workspace_name, <5 more arguments>)
	File "/root/.cache/bazel/_bazel_root/f8087e59fd95af1ae29e8fcb7ff1a3dc/external/rules_foreign_cc/tools/build_defs/configure_script.bzl", line 71, in get_env_vars
		vars["LDFLAGS"]
key "LDFLAGS" not found in dictionary
INFO: Repository boringssl instantiated at:
  no stack (--record_rule_instantiation_callstack not enabled)
Repository rule http_archive defined at:
  /root/.cache/bazel/_bazel_root/f8087e59fd95af1ae29e8fcb7ff1a3dc/external/bazel_tools/tools/build_defs/repo/http.bzl:336:16: in <toplevel>
ERROR: Analysis of target '//source/exe:envoy-static' failed; build aborted: Analysis of target '@envoy//bazel/foreign_cc:luajit' failed
INFO: Elapsed time: 26.319s
INFO: 0 processes.
FAILED: Build did NOT complete successfully (454 packages loaded, 12661 targets configured)
    Fetching @com_github_gperftools_gperftools; Patching repository 9s
    Fetching @org_golang_x_tools; Cloning c9f9432ec4b21a28c4d47f172513698febb68e9c of https://go.googlesource.com/tools 5s
    Fetching @com_github_golang_protobuf; Cloning 6c65a5562fc06764971b7c5d05c76c75e84bdbf7 of https://github.com/golang/protobuf
$

I'm using a container image for this, so anyone should be able to reproduce easily:

git remote add errordeveloper https://github.com/errordeveloper/envoy
git fetch errordeveloper
git checkout errordeveloper/cross-aarch64 -b cross-aarch64

docker run \
  --volume "$(pwd):/src" \
  --workdir "/src" \
  --rm --tty --interactive \
    docker.io/cilium/image-compilers:ac609e4c5a77e9c4c92e096b8c96a49b78d5c869 \
      bazel build --config=cross_aarch64  //source/exe:envoy-static

I'd love some help here, would be happy to contribute back once I have it working!

[errordeveloper]

I have looked into rules_foreign_cc, but I fail to understand what is really going on there really.

[errordeveloper]

More specifically, what I don't get is:

• what exactly rules_foreign_cc is trying to do?
• how is vars["LDFLAGS"] set normally and why it doesn't get set in my case?

[errordeveloper]

I have managed to overcome the LDFLAGS issue with a fairly simple fix (bazel-contrib/rules_foreign_cc#407). I'll share an update if I run into anything else, or will be sure to close the issue otherwise.

[errordeveloper]

For the record, bazel-contrib/rules_foreign_cc#407 has been merged and I'll open a PR here to update the dependency.

[errordeveloper]

Good news: I have built Envoy successfully now, yet with quite a few tweaks, which can be found in my branch. I'd like to open a PR at some point, but it would help if someone could help me to resolve some of the underlying issues that I've managed to bypass.