env2mfile: Base cpu on DEB_HOST_GNU_CPU unless DEB_HOST_ARCH is special

`DEB_HOST_ARCH` encodes both the CPU family and the OS, so using it to
get the CPU type gives the wrong answer for non-Linux ports.

However, `DEB_HOST_GNU_CPU` gives less detailed information about the
CPU: it's `arm` for all 32-bit ARM CPUs, and doesn't distinguish between
the differing baselines of `armel` (ARMv5 softfloat) and `armhf`
(ARMv7 hardfloat).

When cross-compiling for x86_64 Linux, this changes the `cpu()` from
`amd64` to `x86_64`, which is consistent with the answer we get during
native builds on that architecture.

When cross-compiling for `ppc64el`, this changes the `cpu()` from
`ppc64el` to `ppc64`, which is a reasonable change but is still not
consistent with what we see during native builds (which is `ppc64le`):
see #13741 for that.

Resolves: https://github.com/mesonbuild/meson/issues/13742
Signed-off-by: Simon McVittie <smcv@debian.org>

mesonbuild/scripts/env2mfile.py

@@ -130,14 +130,20 @@ def get_args_from_envvars(infos: MachineInfo) -> None:
     if objcpp_link_args:
         infos.link_args['objcpp'] = objcpp_link_args
 
+# map from DEB_HOST_GNU_CPU to Meson machine.cpu_family()
 deb_cpu_family_map = {
     'mips64el': 'mips64',
     'i686': 'x86',
     'powerpc64le': 'ppc64',
 }
 
-deb_cpu_map = {
+# map from DEB_HOST_ARCH to Meson machine.cpu()
+deb_arch_cpu_map = {
     'armhf': 'arm7hlf',
+}
+
+# map from DEB_HOST_GNU_CPU to Meson machine.cpu()
+deb_cpu_map = {
     'mips64el': 'mips64',
     'powerpc64le': 'ppc64',
 }
@@ -202,7 +208,8 @@ def dpkg_architecture_to_machine_info(output: str, options: T.Any) -> MachineInf
     host_subsystem = host_os
     host_kernel = replace_special_cases(deb_kernel_map, data['DEB_HOST_ARCH_OS'])
     host_cpu_family = replace_special_cases(deb_cpu_family_map, data['DEB_HOST_GNU_CPU'])
-    host_cpu = replace_special_cases(deb_cpu_map, data['DEB_HOST_ARCH'])
+    host_cpu = deb_arch_cpu_map.get(data['DEB_HOST_ARCH'],
+                                    replace_special_cases(deb_cpu_map, data['DEB_HOST_GNU_CPU']))
     host_endian = data['DEB_HOST_ARCH_ENDIAN']
 
     compilerstems = [('c', 'gcc'),

unittests/internaltests.py

@@ -1835,9 +1835,7 @@ class InternalTests(unittest.TestCase):
                     system='linux',
                     subsystem='linux',
                     kernel='linux',
-                    # TODO: In native builds we get x86_64, but in
+                    cpu='x86_64',
-                    # cross-builds it's amd64
-                    cpu='TODO',
                     cpu_family='x86_64',
                     endian='little',
                 ),
@@ -1940,8 +1938,7 @@ class InternalTests(unittest.TestCase):
                     # fail when kernel() is called.
                     # https://github.com/mesonbuild/meson/issues/13740
                     kernel='TODO',
-                    # TODO: Currently hurd-i386, but should be i686
+                    cpu='i686',
-                    cpu='TODO',
                     cpu_family='x86',
                     endian='little',
                 ),
@@ -1980,8 +1977,7 @@ class InternalTests(unittest.TestCase):
                     system='kfreebsd',
                     subsystem='kfreebsd',
                     kernel='freebsd',
-                    # TODO: Currently kfreebsd-amd64 but should be x86_64
+                    cpu='x86_64',
-                    cpu='TODO',
                     cpu_family='x86_64',
                     endian='little',
                 ),
@@ -2059,8 +2055,7 @@ class InternalTests(unittest.TestCase):
                     system='linux',
                     subsystem='linux',
                     kernel='linux',
-                    # TODO: Currently ppc64el, but native builds have ppc64le,
+                    # TODO: Currently ppc64, but native builds have ppc64le
-                    # and maybe it should be ppc64 in both cases?
                     # https://github.com/mesonbuild/meson/issues/13741
                     cpu='TODO',
                     cpu_family='ppc64',