--- a/build/templates.mozbuild
+++ b/build/templates.mozbuild
@@ -57,35 +57,32 @@ def Library(name):
 def AllowCompilerWarnings():
     COMPILE_FLAGS['WARNINGS_AS_ERRORS'] = []
 
 @template
 def DisableCompilerWarnings():
     COMPILE_FLAGS['WARNINGS_CFLAGS'] = []
 
 @template
-def RustLibrary(name, features=None, target_dir=None, output_category=None):
+def RustLibrary(name, features=None, output_category=None):
     '''Template for Rust libraries.'''
     Library(name)
 
     IS_RUST_LIBRARY = True
     # Some Rust build scripts compile C/C++ sources, don't error on warnings for them.
     AllowCompilerWarnings()
 
     # And furthermore, don't even show warnings for them, so they don't regress
     # the Compiler Warnings build metric
     # <https://developer.mozilla.org/en-US/docs/Mozilla/Performance/Automated_Performance_Testing_and_Sheriffing/Build_Metrics#compiler_warnings>.
     DisableCompilerWarnings()
 
     if features:
         RUST_LIBRARY_FEATURES = features
 
-    if target_dir:
-        RUST_LIBRARY_TARGET_DIR = target_dir
-
     if output_category:
         RUST_LIBRARY_OUTPUT_CATEGORY = output_category
 
 
 @template
 def SharedLibrary(name, output_category=None):
     '''Template for shared libraries.'''
     Library(name)

--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -524,17 +524,17 @@ class TreeMetadataEmitter(LoggingMixin):
                 context)
 
         crate_type = crate_type[0]
         if crate_type != 'staticlib':
             raise SandboxValidationError(
                 'crate-type %s is not permitted for %s' % (crate_type, libname),
                 context)
 
-        cargo_target_dir = context.get('RUST_LIBRARY_TARGET_DIR', '.')
+        cargo_target_dir = context.config.topobjdir
 
         dependencies = set(config.get('dependencies', {}).iterkeys())
 
         features = context.get(cls.FEATURES_VAR, [])
         unique_features = set(features)
         if len(features) != len(unique_features):
             raise SandboxValidationError(
                 'features for %s should not contain duplicates: %s' % (libname, features),

--- a/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
+++ b/python/mozbuild/mozbuild/test/backend/test_recursivemake.py
@@ -832,51 +832,51 @@ class TestRecursiveMakeBackend(BackendTe
         env = self._consume('rust-library', RecursiveMakeBackend)
 
         backend_path = mozpath.join(env.topobjdir, 'backend.mk')
         lines = [l.strip() for l in open(backend_path, 'rt').readlines()[2:]
                  # Strip out computed flags, they're a PITA to test.
                  if not l.startswith('COMPUTED_')]
 
         expected = [
-            'RUST_LIBRARY_FILE := ./x86_64-unknown-linux-gnu/release/libtest_library.a',
+            'RUST_LIBRARY_FILE := %s/x86_64-unknown-linux-gnu/release/libtest_library.a' % env.topobjdir,
             'CARGO_FILE := $(srcdir)/Cargo.toml',
             'CARGO_TARGET_DIR := %s' % env.topobjdir,
         ]
 
         self.assertEqual(lines, expected)
 
     def test_host_rust_library(self):
         """Test that a Rust library is written to backend.mk correctly."""
         env = self._consume('host-rust-library', RecursiveMakeBackend)
 
         backend_path = mozpath.join(env.topobjdir, 'backend.mk')
         lines = [l.strip() for l in open(backend_path, 'rt').readlines()[2:]
                  # Strip out computed flags, they're a PITA to test.
                  if not l.startswith('COMPUTED_')]
 
         expected = [
-            'HOST_RUST_LIBRARY_FILE := ./x86_64-unknown-linux-gnu/release/libhostrusttool.a',
+            'HOST_RUST_LIBRARY_FILE := %s/x86_64-unknown-linux-gnu/release/libhostrusttool.a' % env.topobjdir,
             'CARGO_FILE := $(srcdir)/Cargo.toml',
             'CARGO_TARGET_DIR := %s' % env.topobjdir,
         ]
 
         self.assertEqual(lines, expected)
 
     def test_host_rust_library_with_features(self):
         """Test that a host Rust library with features is written to backend.mk correctly."""
         env = self._consume('host-rust-library-features', RecursiveMakeBackend)
 
         backend_path = mozpath.join(env.topobjdir, 'backend.mk')
         lines = [l.strip() for l in open(backend_path, 'rt').readlines()[2:]
                  # Strip out computed flags, they're a PITA to test.
                  if not l.startswith('COMPUTED_')]
 
         expected = [
-            'HOST_RUST_LIBRARY_FILE := ./x86_64-unknown-linux-gnu/release/libhostrusttool.a',
+            'HOST_RUST_LIBRARY_FILE := %s/x86_64-unknown-linux-gnu/release/libhostrusttool.a' % env.topobjdir,
             'CARGO_FILE := $(srcdir)/Cargo.toml',
             'CARGO_TARGET_DIR := %s' % env.topobjdir,
             'HOST_RUST_LIBRARY_FEATURES := musthave cantlivewithout',
         ]
 
         self.assertEqual(lines, expected)
 
     def test_rust_library_with_features(self):
@@ -884,17 +884,17 @@ class TestRecursiveMakeBackend(BackendTe
         env = self._consume('rust-library-features', RecursiveMakeBackend)
 
         backend_path = mozpath.join(env.topobjdir, 'backend.mk')
         lines = [l.strip() for l in open(backend_path, 'rt').readlines()[2:]
                  # Strip out computed flags, they're a PITA to test.
                  if not l.startswith('COMPUTED_')]
 
         expected = [
-            'RUST_LIBRARY_FILE := ./x86_64-unknown-linux-gnu/release/libfeature_library.a',
+            'RUST_LIBRARY_FILE := %s/x86_64-unknown-linux-gnu/release/libfeature_library.a' % env.topobjdir,
             'CARGO_FILE := $(srcdir)/Cargo.toml',
             'CARGO_TARGET_DIR := %s' % env.topobjdir,
             'RUST_LIBRARY_FEATURES := musthave cantlivewithout',
         ]
 
         self.assertEqual(lines, expected)
 
     def test_rust_programs(self):

--- a/toolkit/library/gtest/rust/moz.build
+++ b/toolkit/library/gtest/rust/moz.build
@@ -1,10 +1,10 @@
 # -*- Mode: python; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 40 -*-
 # vim: set filetype=python:
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 include('../../rust/gkrust-features.mozbuild')
 
-RustLibrary('gkrust-gtest', gkrust_features, '../..',
+RustLibrary('gkrust-gtest', gkrust_features,
             output_category=None if CONFIG['LINK_GTEST_DURING_COMPILE'] else 'gtest')

--- a/toolkit/library/rust/moz.build
+++ b/toolkit/library/rust/moz.build
@@ -1,17 +1,17 @@
 # -*- Mode: python; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 40 -*-
 # vim: set filetype=python:
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 include('gkrust-features.mozbuild')
 
-RustLibrary('gkrust', gkrust_features, '..')
+RustLibrary('gkrust', gkrust_features)
 
 # Target directory doesn't matter a lot here, since we can't share panic=abort
 # compilation artifacts with gkrust.
 RUST_TESTS = [
     'selectors',
     'servo_arc',
     'stylo_tests',
 ]