--- original/rust-1.42.0.ebuild	2020-03-19 21:58:58.436775758 -0700
+++ rust-1.42.0.ebuild	2020-03-19 21:58:58.438775758 -0700
@@ -18,7 +18,7 @@
 	SLOT="stable/${ABI_VER}"
 	MY_P="rustc-${PV}"
 	SRC="${MY_P}-src.tar.xz"
-	KEYWORDS="~amd64 ~arm ~arm64 ~ppc64 ~x86"
+	KEYWORDS="amd64 ~arm ~arm64 ~ppc64 ~x86"
 fi
 
 RUST_STAGE0_VERSION="1.$(($(ver_cut 2) - 1)).1"
@@ -322,6 +322,24 @@
 
 	dodoc COPYRIGHT
 
+	cat <<-EOF > "${T}"/50${P}
+		RUST_SRC_PATH="/usr/lib/rustlib/src/rust/src/"
+		CARGO_TARGET_DIR_PREFIX="/tmp/rust-build-artifacts/"
+	EOF
+	doenvd "${T}"/50${P}
+
+	# We want gdb to automatically find the correct Rust sources
+	# (as installed by this ebuild). Note that automatical sourcing of
+	# this file requires a patched gdb.
+	# TODO: We should be able to use rust-gdb's
+	#       GDB_PYTHON_MODULE_DIRECTORY instead! It's cleaner and does
+	#       not rely on a patched gdb.
+	cat <<-EOF > "${T}/rust.gdb"
+		set substitute-path ${S}/src/ /usr/lib/rustlib/src/rust/src/
+	EOF
+	insinto /usr/share/gdb/
+	doins "${T}/rust.gdb"
+
 	# note: eselect-rust adds EROOT to all paths below
 	cat <<-EOF > "${T}/provider-${P}"
 		/usr/bin/rustdoc
@@ -376,6 +394,11 @@
 		ewarn "error: cannot produce proc-macro for serde_derive v1.0.98 as the target "
 		ewarn "x86_64-unknown-linux-musl does not support these crate types"
 	fi
+
+	elog
+	elog "In order for CARGO_TARGET_DIR_PREFIX to be set properly, please run"
+	elog "env-update && source /etc/profile"
+	elog
 }
 
 pkg_postrm() {