Add support of cross-building the engine for ARM64 Linux Host (#390)

Added cross-building Flutter Engine for ARM64 Linux platforms. This PR is part of ARM64 Linux support in the Flutter SDK.

Author: Hidenori Matsubayashi

AUTHORS

@@ -6,3 +6,4 @@
 Google Inc.
 Jim Simon <jim.j.simon@gmail.com>
 The Fuchsia Authors
+Hidenori Matsubayashi <Hidenori.Matsubayashi@sony.com>

build/config/sysroot.gni

@@ -27,8 +27,12 @@ if (current_toolchain == default_toolchain && target_sysroot != "") {
 } else if (is_linux && !is_chromeos) {
   if (current_cpu == "mipsel") {
     sysroot = rebase_path("//mipsel-sysroot/sysroot")
-  } else if (use_default_linux_sysroot && !is_fuchsia && current_cpu == "x64") {
-    sysroot = rebase_path("//build/linux/debian_sid_amd64-sysroot")
+  } else if (use_default_linux_sysroot && !is_fuchsia) {
+    if (current_cpu == "x64") {
+      sysroot = rebase_path("//build/linux/debian_sid_amd64-sysroot")
+    } else {
+      sysroot = rebase_path("//build/linux/debian_sid_arm64-sysroot")
+    }
     assert(
         exec_script("//build/dir_exists.py", [ sysroot ], "string") == "True",
         "Missing sysroot ($sysroot). To fix, run: build/linux/sysroot_scripts/install-sysroot.py --arch=$current_cpu")

build/toolchain/gcc_toolchain.gni

@@ -45,6 +45,9 @@ analyzer_wrapper =
 #      Location of the strip executable. When specified, strip will be run on
 #      all shared libraries and executables as they are built. The pre-stripped
 #      artifacts will be put in lib.stripped/ and exe.stripped/.
+#  - llvm_objcopy
+#      Location of the llvm-objcopy executable. Used as strip instead of strip
+#      when specified.
 template("gcc_toolchain") {
   toolchain(target_name) {
     assert(defined(invoker.cc), "gcc_toolchain() must specify a \"cc\" value")
@@ -169,7 +172,7 @@ template("gcc_toolchain") {
       tocfile = sofile + ".TOC"
       temporary_tocname = sofile + ".tmp"
       link_command = "$ld -shared {{ldflags}} $coverage_flags -o $sofile -Wl,--build-id=sha1 -Wl,-soname=$soname @$rspfile"
-      toc_command = "{ $readelf -d $sofile | grep SONAME ; $nm -gD -f p $sofile | cut -f1-2 -d' '; } > $temporary_tocname"
+      toc_command = "{ $readelf -d $sofile | grep SONAME ; $nm -gD -f posix $sofile | cut -f1-2 -d' '; } > $temporary_tocname"
       replace_command = "if ! cmp -s $temporary_tocname $tocfile; then mv $temporary_tocname $tocfile; fi"
 
       command = "$link_command && $toc_command && $replace_command"
@@ -214,7 +217,7 @@ template("gcc_toolchain") {
       rspfile = "$outfile.rsp"
       unstripped_outfile = outfile
 
-      if (defined(invoker.strip)) {
+      if (defined(invoker.strip) || defined(invoker.llvm_objcopy)) {
         unstripped_outfile = "{{root_out_dir}}/exe.unstripped/$exename"
       }
 
@@ -224,6 +227,10 @@ template("gcc_toolchain") {
         strip_command =
             "${strip} --strip-unneeded -o $outfile $unstripped_outfile"
         command += " && " + strip_command
+      } else if (defined(invoker.llvm_objcopy)) {
+        strip = invoker.llvm_objcopy
+        strip_command = "${strip} --strip-all $unstripped_outfile $outfile"
+        command += " && " + strip_command
       }
       if (defined(invoker.postlink)) {
         command += " && " + invoker.postlink

build/toolchain/linux/BUILD.gn

@@ -97,10 +97,10 @@ gcc_toolchain("clang_arm64") {
   cxx = "${compiler_prefix}$prefix/clang++"
 
   readelf = "readelf"
-  nm = "nm"
-  ar = "ar"
+  nm = "${prefix}/llvm-nm"
+  ar = "${prefix}/llvm-ar"
   ld = cxx
-  strip = "strip"
+  llvm_objcopy = "${prefix}/llvm-objcopy"
 
   toolchain_cpu = "arm64"
   toolchain_os = "linux"