image: Pass the image's architecture to repart

image/compose.bzl

@@ -292,6 +292,7 @@ def _bootable_disk_image_impl(ctx: AnalysisContext) -> list[Provider]:
     system = declare_repart(
         ctx,
         tools = tools,
+        systemd_arch = ARCHITECTURES[ctx.attrs.arch].systemd,
         basename = basename,
         definitions = system_definitions,
         disk = False,
@@ -334,6 +335,7 @@ def _bootable_disk_image_impl(ctx: AnalysisContext) -> list[Provider]:
     disk = declare_repart(
         ctx,
         tools = tools,
+        systemd_arch = ARCHITECTURES[ctx.attrs.arch].systemd,
         basename = basename,
         definitions = boot_definitions,
         identifier = "disk",

image_format/disk.bzl

@@ -26,6 +26,7 @@ load(
     "resolve_signing_key",
     "signing_key_spec",
 )
+load("//platforms:architecture.bzl", "ARCHITECTURES", "architecture")
 
 Partition = dict[str, typing.Any]
 
@@ -283,6 +284,7 @@ def declare_repart(
     *,
     tools: ImageToolsInfo,
     image: ImageInfo,
+    systemd_arch: str,
     definitions: list[str],
     disk: bool = True,
     split: bool = False,
@@ -377,6 +379,7 @@ def declare_repart(
         written.append(WrittenPartitionInfo(definition = definition, manifest = listing))
 
     spec = {
+        "architecture": systemd_arch,
         "basename": basename,
         "definitions": definition_specs,
         "identity": "{}[{}]".format(ctx.label, identifier or "repart"),
@@ -481,6 +484,7 @@ def _repart_impl(ctx: AnalysisContext) -> list[Provider]:
     result = declare_repart(
         ctx,
         tools = ctx.attrs._tools[ImageToolsInfo],
+        systemd_arch = ARCHITECTURES[ctx.attrs._arch].systemd,
         basename = ctx.attrs.basename,
         definitions = ctx.attrs.definitions,
         disk = ctx.attrs.disk,
@@ -540,6 +544,8 @@ _repart = rule(
             doc = "split repart targets whose partitions should be copied into the result",
         ),
         "split": attrs.bool(default = False, doc = "also emit independent artifacts for new partitions"),
+        # `_arch` is the architecture the image runs on. repart picks the partition types for it.
+        "_arch": attrs.string(default = architecture.configured()),
     }
     | IMAGE_TOOLS_ATTR,
 )

image_format/disk.py

@@ -51,6 +51,9 @@ class ImportedPartitionSpec(TypedDict):
 
 class Spec(finalize.ImageSpec):
     out: str | None
+    # The systemd spelling of the architecture the image runs on. repart picks the partition types of
+    # root and usr partitions for it.
+    architecture: str
     # What the artifacts of this invocation are named after, extension aside.
     basename: str
     # Stable target identity the seed derives from, unless one is given outright.
@@ -360,6 +363,7 @@ def main(argv: list[str] | None = None) -> None:
             str(seed),
             "--definitions",
             str(repart_definitions),
+            f"--architecture={spec['architecture']}",
         ]
         if splits:
             cmd.append("--split=yes")

image_format/sysext.bzl

@@ -122,6 +122,8 @@ def declare_image_sysext(
         exe = tools.sysext,
         image = image,
         spec = {
+            # repart has no partition type for any architecture, so an `_any` DDI gets the build host's types.
+            "architecture": None if systemd_arch == "_any" else systemd_arch,
             "base": layers,
             "identity": str(ctx.label),
             "manifest": manifest.as_output(),

image_format/sysext.py

@@ -39,6 +39,9 @@ class Spec(finalize.ImageSpec):
     # Where to write the DDI's verity root hash: the identity a host reports
     # for the merged extension, published so consumers can join on it.
     root_hash_out: str
+    # The systemd spelling of the architecture the extension merges on. repart picks the partition
+    # types for it. With None, repart uses the build host's types.
+    architecture: str | None
 
 
 _SEED_NAMESPACE = uuid.UUID("b388a973-3ffa-44aa-90b7-afcc4573ea9f")
@@ -139,6 +142,8 @@ def main(argv: list[str] | None = None) -> None:
             "--seed",
             str(seed),
         ]
+        if spec["architecture"] is not None:
+            cmd.append(f"--architecture={spec['architecture']}")
         # The built-in sysext definitions always include the signature partition, and repart
         # refuses to fill it without a key, so an unsigned DDI must drop it instead.
         if spec["signing"]: