Support LOCAL_MODULE_RELATIVE_PATH

Most users of LOCAL_MODULE_PATH are setting a subdirectory of the
normal install path, for example to install HALs into system/lib/hw.
This is problematic for multiarch builds, where the install location
depends on the arch.  Allow modules to specify LOCAL_MODULE_RELATIVE_PATH.
HALs will generally use:
LOCAL_MODULE_RELATIVE_PATH := hw

Change-Id: I4e4ceec61d026bbe74ba604554c06104bde42e5e

core/base_rules.mk

@@ -99,6 +99,7 @@ endif
 
 ifneq (true,$(LOCAL_UNINSTALLABLE_MODULE))
 my_module_path := $(strip $(LOCAL_MODULE_PATH))
+my_module_relative_path := $(strip $(LOCAL_MODULE_RELATIVE_PATH))
 ifeq ($(my_module_path),)
   ifdef LOCAL_IS_HOST_MODULE
     partition_tag :=
@@ -121,6 +122,9 @@ ifeq ($(my_module_path),)
     $(error $(LOCAL_PATH): unhandled install path "$(install_path_var) for $(LOCAL_MODULE)")
   endif
 endif
+ifneq ($(my_module_relative_path),)
+  my_module_path := $(my_module_path)/$(my_module_relative_path)
+endif
 endif # not LOCAL_UNINSTALLABLE_MODULE
 
 ifneq ($(strip $(LOCAL_BUILT_MODULE)$(LOCAL_INSTALLED_MODULE)),)

core/build-system.html

@@ -383,7 +383,7 @@ the rest of them easier to read, and you can always refer back to the templates
 if you need them again later.</p>
 <p>By default, on the target these are built into /system/bin, and on the
 host, they're built into <combo>/host/bin.  These can be overridden by setting
-<code>LOCAL_MODULE_PATH</code>.  See
+<code>LOCAL_MODULE_PATH</code> or <code>LOCAL_MODULE_RELATIVE_PATH</code>.  See
 <a href="#moving-targets">Putting targets elsewhere</a>
 for more.</p>
 
@@ -533,16 +533,27 @@ endif
 
 <h3><a name="moving-modules"/>Putting modules elsewhere</h3>
 <p>If you have modules that normally go somewhere, and you need to have them
-build somewhere else, read this.  One use of this is putting files on
-the root filesystem instead of where they normally go in /system. Add these
-lines to your Android.mk:</p>
+build somewhere else, read this.</p>
+<p>If you have modules that need to go in a subdirectory of their normal
+location, for example HAL modules that need to go in /system/lib/hw or
+/vendor/lib/hw, set LOCAL_MODULE_RELATIVE_PATH in your Android.mk, for
+example:</p>
+<pre>
+LOCAL_MODULE_RELATIVE_PATH := hw
+</pre>
+<p>If you have modules that need to go in an entirely different location, for
+example the root filesystem instead of in /system, add these lines to your
+Android.mk:</p>
 <pre>
 LOCAL_MODULE_PATH := $(TARGET_ROOT_OUT_SBIN)
 LOCAL_UNSTRIPPED_PATH := $(TARGET_ROOT_OUT_SBIN_UNSTRIPPED)
 </pre>
-<p>For executables and libraries, you need to also specify a
-<code>LOCAL_UNSTRIPPED_PATH</code> location, because on target builds, we keep
-the unstripped executables so GDB can find the symbols.</code>
+<p>For executables and libraries, you need to specify a
+<code>LOCAL_UNSTRIPPED_PATH</code> location if you specified a
+<code>LOCAL_MODULE_PATH</code>, because on target builds, we keep
+the unstripped executables so GDB can find the symbols.
+<code>LOCAL_UNSTRIPPED_PATH</code> is not necessary if you only specified
+<code>LOCAL_MODULE_RELATIVE_PATH</code>.</p>
 <p>Look in <code>config/envsetup.make</code> for all of the variables defining
 places to build things.</p>
 <p>FYI: If you're installing an executable to /sbin, you probably also want to
@@ -818,6 +829,13 @@ so the unstripped binary has somewhere to go.  An error will occur if you forget
 to.</p>
 <p>See <a href="#moving-modules">Putting modules elsewhere</a> for more.</p>
 
+<h4>LOCAL_MODULE_RELATIVE_PATH</h4>
+<p>Instructs the build system to put the module in a subdirectory under the
+directory that is normal for its type.  If you set this you do not need to
+set <code>LOCAL_UNSTRIPPED_PATH</code>, the unstripped binaries will also use
+the relative path.</p>
+<p>See <a href="#moving-modules">Putting modules elsewhere</a> for more.</p>
+
 <h4>LOCAL_UNSTRIPPED_PATH</h4>
 <p>Instructs the build system to put the unstripped version of the module
 somewhere other than what's normal for its type.  Usually, you override this

core/clear_vars.mk

@@ -4,6 +4,7 @@
 
 LOCAL_MODULE:=
 LOCAL_MODULE_PATH:=
+LOCAL_MODULE_RELATIVE_PATH :=
 LOCAL_MODULE_STEM:=
 LOCAL_DONT_CHECK_MODULE:=
 LOCAL_CHECKED_MODULE:=