tooling: define aarch64 toolchain

Use gcc to cross-compilation for aarch64, as clang requires
additional setup.
Clang support can be added on a follow-up.

BUILD

@@ -1,7 +0,0 @@
-filegroup(
-    name = "clang_tidy_config",
-    srcs = [
-        ".clang-tidy",
-    ],
-    visibility = ["//visibility:public"],
-)

Dockerfile

@@ -43,8 +43,12 @@ RUN apt-get update && apt-get install -y \
     clang-format-18 \
     clang-tidy-18 \
     lld-18 \
-    lldb-18 \
-    && rm -rf /var/lib/apt/lists/*
+    lldb-18
+
+# Cross-compilation
+RUN apt-get install -y \
+    gcc-aarch64-linux-gnu \
+    g++-aarch64-linux-gnu
 
 RUN pip install yamllint
 

MODULE.bazel

@@ -20,5 +20,6 @@ git_override(
 bazel_dep(name = "platforms", version = "0.0.10")
 
 register_toolchains(
-    "//toolchain:cc_toolchain_for_linux_x86_64",
+    "//toolchain/x86_64_linux",
+    "//toolchain/aarch64_linux",
 )

bazel/platforms/BUILD

@@ -0,0 +1,33 @@
+config_setting(
+    name = "x86_64_config",
+    constraint_values = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:linux",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+config_setting(
+    name = "aarch64_config",
+    constraint_values = [
+        "@platforms//cpu:aarch64",
+        "@platforms//os:linux",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+platform(
+    name = "x86_64_linux",
+    constraint_values = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:linux",
+    ],
+)
+
+platform(
+    name = "aarch64_linux",
+    constraint_values = [
+        "@platforms//cpu:aarch64",
+        "@platforms//os:linux",
+    ],
+)

examples/cpp/BUILD

@@ -2,17 +2,19 @@ cc_library(
     name = "lib",
     srcs = ["hello.cpp"],
     hdrs = ["hello.hpp"],
-    features = [
-        "warnings_critical_code",
-    ],
+    features = select({
+        "//bazel/platforms:aarch64_config": ["warnings_critical_code_gcc"],
+        "//conditions:default": ["warnings_critical_code_clang"],
+    }),
 )
 
 cc_binary(
     name = "bin",
     srcs = ["main.cpp"],
-    features = [
-        "warnings_critical_code",
-    ],
+    features = select({
+        "//bazel/platforms:aarch64_config": ["warnings_critical_code_gcc"],
+        "//conditions:default": ["warnings_critical_code_clang"],
+    }),
     deps = [
         ":lib",
     ],

toolchain/BUILD

@@ -1,34 +0,0 @@
-load(":cc_toolchain_config.bzl", "cc_toolchain_config")
-
-package(default_visibility = ["//visibility:public"])
-
-filegroup(name = "empty")
-
-cc_toolchain_config(name = "linux_x86_64_toolchain_config")
-
-cc_toolchain(
-    name = "linux_x86_64_toolchain",
-    all_files = ":empty",
-    compiler_files = ":empty",
-    dwp_files = ":empty",
-    linker_files = ":empty",
-    objcopy_files = ":empty",
-    strip_files = ":empty",
-    supports_param_files = 0,
-    toolchain_config = ":linux_x86_64_toolchain_config",
-    toolchain_identifier = "linux_x86_64_toolchain",
-)
-
-toolchain(
-    name = "cc_toolchain_for_linux_x86_64",
-    exec_compatible_with = [
-        "@platforms//cpu:x86_64",
-        "@platforms//os:linux",
-    ],
-    target_compatible_with = [
-        "@platforms//cpu:x86_64",
-        "@platforms//os:linux",
-    ],
-    toolchain = ":linux_x86_64_toolchain",
-    toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
-)

toolchain/aarch64_linux/BUILD

@@ -0,0 +1,34 @@
+load("//toolchain/aarch64_linux:cc_toolchain_config.bzl", "cc_toolchain_config")
+
+package(default_visibility = ["//visibility:public"])
+
+filegroup(name = "empty")
+
+cc_toolchain_config(name = "toolchain_config")
+
+cc_toolchain(
+    name = "cc_toolchain",
+    all_files = ":empty",
+    compiler_files = ":empty",
+    dwp_files = ":empty",
+    linker_files = ":empty",
+    objcopy_files = ":empty",
+    strip_files = ":empty",
+    supports_param_files = 0,
+    toolchain_config = ":toolchain_config",
+    toolchain_identifier = "aarch64_linux_toolchain",
+)
+
+toolchain(
+    name = "aarch64_linux",
+    exec_compatible_with = [
+        "@platforms//cpu:x86_64",
+        "@platforms//os:linux",
+    ],
+    target_compatible_with = [
+        "@platforms//cpu:aarch64",
+        "@platforms//os:linux",
+    ],
+    toolchain = "cc_toolchain",
+    toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
+)