Make --host work for ./build-userland, ./build-dhrystone, etc. in addition to just ./build-modules

README.adoc

@@ -921,7 +921,7 @@ It has however severe limitations:
 Still interested?
 
 ....
-./build-modules --gcc-which host --host
+./build-modules --host
 ....
 
 Compilation will likely fail for some modules because of kernel or toolchain differences that we can't control on the host.
@@ -929,7 +929,7 @@ Compilation will likely fail for some modules because of kernel or toolchain dif
 The best workaround is to compile just your modules with:
 
 ....
-./build-modules --gcc-which host --host -- hello hello2
+./build-modules --host -- hello hello2
 ....
 
 which is equivalent to:
@@ -14514,6 +14514,8 @@ git submodule update --init submodules/dhrystone
 ./run --userland "$(./getvar userland_build_dir)/submodules/dhrystone/dhrystone"
 ....
 
+TODO automate run more nicely to dispense `getvar`.
+
 Increase the number of loops to try and reach more meaningful results:
 
 ....
@@ -14527,7 +14529,12 @@ Build and run on gem5 user mode:
 ./run --emulator gem5 --userland "$(./getvar --static userland_build_dir)/submodules/dhrystone/dhrystone"
 ....
 
-TODO automate run more nicely.
+Run natively on the host:
+
+....
+./build-dhrystone --host
+"$(./getvar --host userland_build_dir)/submodules/dhrystone/dhrystone"
+....
 
 Build for <<baremetal>> execution and run it in baremetal QEMU. TODO: fix the build, just need to factor out all run arguments from link:build-baremetal[] into link:common.py[] and it should just work, no missing syscalls.
 

build-modules

@@ -23,14 +23,6 @@ See also: https://cirosantilli.com/linux-kernel-module-cheat#host
             default='',
             help='''
 Pass custom options to make.
-''',
-        )
-        self.add_argument(
-            '--host',
-            default=False,
-            help='''\
-Build the Linux kernel modules against the host kernel.
-Place the modules on a separate magic directory from non --host builds.
 ''',
         )
         self._add_argument('--force-rebuild')

common.py

@@ -499,6 +499,17 @@ options are given, for example --static, since users don't usually want
 static executables to be placed in the final image, but rather only for
 user mode simulations in simulators that don't support dynamic linking like gem5.
 '''
+        )
+        self.add_argument(
+            '--host',
+            default=False,
+            help='''\
+Use the host toolchain and other dependencies to build exectuables for host execution.
+Automatically place the build output on a separate directory from non --host builds,
+e.g. by defaulting --userland-build-id host if that option has effect for the package.
+Make --copy-overlay default to False as the generated executables can't in general
+be run in the guest.
+''',
         )
         self.add_argument(
             '--out-rootfs-overlay-dir-prefix',
@@ -694,6 +705,8 @@ Incompatible archs are skipped.
         if not env['_args_given']['userland_build_id']:
             if env['static']:
                 env['userland_build_id'] = 'static'
+            elif env['host']:
+                env['userland_build_id'] = 'host'
             else:
                 env['userland_build_id'] = env['default_build_id']
         if not env['_args_given']['gem5_build_id']:
@@ -954,7 +967,7 @@ Incompatible archs are skipped.
             env['userland_build_dir'] = join(env['out_dir'], 'userland', env['userland_build_id'], env['arch'])
         env['package'] = set(env['package'])
         if not env['_args_given']['copy_overlay']:
-            if self.env['in_tree'] or self.env['static']:
+            if self.env['in_tree'] or self.env['static'] or self.env['host']:
                 env['copy_overlay'] = False
 
         # Kernel modules.
@@ -1082,6 +1095,8 @@ lunch aosp_{}-eng
         if not env['_args_given']['gcc_which']:
             if env['mode'] == 'baremetal':
                 env['gcc_which'] = 'crosstool-ng'
+            elif env['host']:
+                env['gcc_which'] = 'host'
         if env['gcc_which'] == 'buildroot':
             env['toolchain_prefix'] = os.path.join(
                 env['buildroot_host_bin_dir'],