[draft] Sketched out an explicit QEMU mode

cibuildwheel/linux.py

@@ -11,7 +11,7 @@
 from ._compat.typing import assert_never
 from .architecture import Architecture
 from .logger import log
-from .oci_container import OCIContainer
+from .oci_container import OCIContainer, OCIPlatform
 from .options import Options
 from .typing import PathOrStr
 from .util import (
@@ -28,6 +28,14 @@
     unwrap,
 )
 
+ArchitectureOCIPlatformMap = {
+    Architecture.x86_64: OCIPlatform.AMD64,
+    Architecture.i686: OCIPlatform.i386,
+    Architecture.aarch64: OCIPlatform.ARM64,
+    Architecture.ppc64le: OCIPlatform.PPC64LE,
+    Architecture.s390x: OCIPlatform.S390X,
+}
+
 
 @dataclass(frozen=True)
 class PythonConfiguration:
@@ -431,11 +439,20 @@ def build(options: Options, tmp_path: Path) -> None:  # noqa: ARG001
 
             print(f"info: This container will host the build for {', '.join(ids_to_build)}...")
 
+            for wheel_platform, oci_platform in ArchitectureOCIPlatformMap.items():
+                if build_step.platform_tag.endswith(wheel_platform.name):
+                    this_build_platform = oci_platform
+                    break
+            else:
+                msg = f"Unexpected build platform: {build_step.platform_tag}."
+                raise ValueError(msg)
+
             with OCIContainer(
                 image=build_step.container_image,
                 enforce_32_bit=build_step.platform_tag.endswith("i686"),
                 cwd=container_project_path,
                 engine=options.globals.container_engine,
+                oci_platform=this_build_platform,
             ) as container:
                 build_in_container(
                     options=options,

cibuildwheel/oci_container.py

@@ -12,6 +12,7 @@
 import uuid
 from collections.abc import Mapping, Sequence
 from dataclasses import dataclass
+from enum import Enum
 from pathlib import Path, PurePath, PurePosixPath
 from types import TracebackType
 from typing import IO, Dict, Literal
@@ -29,6 +30,14 @@
 ContainerEngineName = Literal["docker", "podman"]
 
 
+class OCIPlatform(Enum):
+    AMD64 = "linux/amd64"
+    i386 = "linux/386"
+    ARM64 = "linux/arm64"
+    PPC64LE = "linux/ppc64le"
+    S390X = "linux/s390x"
+
+
 @dataclass(frozen=True)
 class OCIContainerEngineConfig:
     name: ContainerEngineName
@@ -111,6 +120,7 @@ def __init__(
         enforce_32_bit: bool = False,
         cwd: PathOrStr | None = None,
         engine: OCIContainerEngineConfig = DEFAULT_ENGINE,
+        oci_platform: OCIPlatform | None = None,
     ):
         if not image:
             msg = "Must have a non-empty image to run."
@@ -121,6 +131,7 @@ def __init__(
         self.cwd = cwd
         self.name: str | None = None
         self.engine = engine
+        self.oci_platform = oci_platform
 
     def __enter__(self) -> Self:
         self.name = f"cibuildwheel-{uuid.uuid4()}"
@@ -149,6 +160,7 @@ def __enter__(self) -> Self:
             [
                 self.engine.name,
                 "create",
+                *((f"--platform={self.oci_platform.value}",) if self.oci_platform else ()),
                 "--env=CIBUILDWHEEL",
                 "--env=SOURCE_DATE_EPOCH",
                 f"--name={self.name}",