build: switch to build settings for static build
This switches the way to select static linking for C builds from a
constraint_setting to a build_setting. The benefit of this is that the
transition to static linking no longer depends on the architecture,
because this setting is not part of the platform anymore.
The alternative would be to select the matching static platform based on
the architecture in the transition implementation. However, I did not
find a good way to obtain the architecture in a transition
implementation. You can access the platform through the settings
parameter, but it's not clear how to extract the architecture from that.
Something that would work is to define an attribute for the architecture
on the rule where the transition is used, and fill this attribute using
a select() at the point where the rule is instantiated. But this
requires changes to all rules which use the transition, which is ugly.
Change-Id: I8962e24b561b8d1724bac785cb3739cdc434d47e
Reviewed-on: https://review.monogon.dev/c/monogon/+/4172
Tested-by: Jenkins CI
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/MODULE.bazel b/MODULE.bazel
index 588fe0d..b73a8eb 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -85,9 +85,7 @@
snapshot = "//build/toolchain/musl-host-gcc:sysroot.tar.xz",
)
-# Register our custom CC toolchains. Order matters - more specific toolchains must be registered first.
-# (host_cc_toolchain won't care about //build/platforms/linkmode, but musl_host_toolchain won't
-# match anything unless its linkmode is set).
+# Register our custom CC toolchains.
register_toolchains("//build/toolchain/musl-host-gcc:musl_host_toolchain")
register_toolchains("//build/toolchain/llvm-efi:efi_k8_toolchain")
diff --git a/build/platforms/BUILD.bazel b/build/platforms/BUILD.bazel
index 217350a..293af9b 100644
--- a/build/platforms/BUILD.bazel
+++ b/build/platforms/BUILD.bazel
@@ -18,18 +18,6 @@
visibility = ["//visibility:public"],
)
-# Linux x86_64 platform with static linking
-# (i.e. Metropolis node, scratch containers...).
-platform(
- name = "linux_amd64_static",
- constraint_values = [
- "@platforms//os:linux",
- "@platforms//cpu:x86_64",
- "//build/platforms/linkmode:musl-static",
- ],
- visibility = ["//visibility:public"],
-)
-
platform(
name = "remote_amd64",
constraint_values = [
diff --git a/build/platforms/linkmode/BUILD.bazel b/build/platforms/linkmode/BUILD.bazel
index 8a7f99c..f749e9d 100644
--- a/build/platforms/linkmode/BUILD.bazel
+++ b/build/platforms/linkmode/BUILD.bazel
@@ -1,14 +1,7 @@
-package(
- default_visibility = ["//visibility:public"],
-)
+load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
-# Minimal Metropolis node environment. No dynamic linker,
-# so everything has to be statically linked.
-constraint_value(
- name = "musl-static",
- constraint_setting = ":linkmode",
-)
-
-constraint_setting(
- name = "linkmode",
+bool_flag(
+ name = "static",
+ build_setting_default = False,
+ visibility = ["//visibility:public"],
)
diff --git a/build/toolchain/BUILD.bazel b/build/toolchain/BUILD.bazel
index c4c5ad8..75cd911 100644
--- a/build/toolchain/BUILD.bazel
+++ b/build/toolchain/BUILD.bazel
@@ -49,6 +49,11 @@
host_cc_toolchain_config(name = "host_cc_k8_toolchain_config")
+config_setting(
+ name = "is_dynamic",
+ flag_values = {"//build/platforms/linkmode:static": "False"},
+)
+
toolchain(
name = "host_cc_toolchain",
exec_compatible_with = [
@@ -59,6 +64,9 @@
"@platforms//os:linux",
"@platforms//cpu:x86_64",
],
+ target_settings = [
+ ":is_dynamic",
+ ],
toolchain = ":host_cc_k8_toolchain",
toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
)
diff --git a/build/toolchain/musl-host-gcc/BUILD.bazel b/build/toolchain/musl-host-gcc/BUILD.bazel
index 39a0eb4..fd7e553 100644
--- a/build/toolchain/musl-host-gcc/BUILD.bazel
+++ b/build/toolchain/musl-host-gcc/BUILD.bazel
@@ -42,6 +42,11 @@
],
)
+config_setting(
+ name = "is_static",
+ flag_values = {"//build/platforms/linkmode:static": "True"},
+)
+
toolchain(
name = "musl_host_toolchain",
exec_compatible_with = [
@@ -51,7 +56,9 @@
target_compatible_with = [
"@platforms//cpu:x86_64",
"@platforms//os:linux",
- "//build/platforms/linkmode:musl-static",
+ ],
+ target_settings = [
+ ":is_static",
],
toolchain = ":musl_host_cc_k8_toolchain",
toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
diff --git a/osbase/build/def.bzl b/osbase/build/def.bzl
index b047d8b..c8ca9dd 100644
--- a/osbase/build/def.bzl
+++ b/osbase/build/def.bzl
@@ -6,7 +6,7 @@
"""
return {
"@io_bazel_rules_go//go/config:static": True,
- "//command_line_option:platforms": "//build/platforms:linux_amd64_static",
+ "//build/platforms/linkmode:static": True,
}
build_static_transition = transition(
@@ -14,7 +14,7 @@
inputs = [],
outputs = [
"@io_bazel_rules_go//go/config:static",
- "//command_line_option:platforms",
+ "//build/platforms/linkmode:static",
],
)
@@ -63,9 +63,7 @@
"@io_bazel_rules_go//go/config:race": False,
"@io_bazel_rules_go//go/config:pure": False,
"@io_bazel_rules_go//go/config:static": False,
-
- # Note: this toolchain is not actually used to perform the build.
- "//command_line_option:platforms": "//build/platforms:linux_amd64_static",
+ "//build/platforms/linkmode:static": False,
}
def _ignore_unused_configuration_impl(_settings, _attr):