[ios] Use generic implementation of libvpx in "catalyst" environment

The linker fails if any object file does not define LC_BUILD_VERSION
when linking a binary for "catalyst" environment. As nasm does not
create such a section, the build fail if using optimised version of
libvpx.

As a workaround, use generic implementation instead of the optimized
one in that configuration (since it is still experimental anyway).

Bug: 1145197, 1138425
Change-Id: I6bf02c499d8e35dcc0fe34f5bb53df230a8449cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2517955
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: James Zern <jzern@google.com>
Cr-Commit-Position: refs/heads/master@{#824389}

build/config/ios/config.gni

+# Copyright 2020 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+declare_args() {
+  # Configure the environment for which to build. Could be either "device",
+  # "simulator" or "catalyst". If unspecified, then it will be assumed to be
+  # "simulator" if the target_cpu is "x68" or "x64", "device" otherwise. The
+  # default is only there for compatibility reasons and will be removed (see
+  # crbug.com/1138425 for more details).
+  target_environment = ""
+}
+
+if (target_environment == "") {
+  if (current_cpu == "x86" || current_cpu == "x64") {
+    target_environment = "simulator"
+  } else {
+    target_environment = "device"
+  }
+}
+
+assert(target_environment == "simulator" || target_environment == "device" ||
+       target_environment == "catalyst")

build/config/ios/ios_sdk.gni

@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/ios/config.gni")
 import("//build/config/ios/ios_sdk_overrides.gni")
 import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
@@ -60,13 +61,6 @@ declare_args() {
 
   # TODO(crbug.com/1015730): remove this flag because ios_use_goma_rbe covers.
   ios_enable_relative_sdk_path = ios_use_goma_rbe
-
-  # Configure the environment for which to build. Could be either "device",
-  # "simulator" or "catalyst". If unspecified, then it will be assumed to be
-  # "simulator" if the target_cpu if "x68" or "x64", "device" otherwise. The
-  # default is only there for compatibility reason and will be removed (see
-  # crbug.com/1138425 for more details).
-  target_environment = ""
 }
 
 declare_args() {
@@ -79,17 +73,6 @@ declare_args() {
   primary_fat_toolchain_name = ""
 }
 
-if (target_environment == "") {
-  if (current_cpu == "x86" || current_cpu == "x64") {
-    target_environment = "simulator"
-  } else {
-    target_environment = "device"
-  }
-}
-
-assert(target_environment == "simulator" || target_environment == "device" ||
-       target_environment == "catalyst")
-
 # Official builds may not use goma.
 assert(!(use_goma && is_chrome_branded && is_official_build &&
              target_cpu == "arm64"),

third_party/libvpx/BUILD.gn

@@ -5,6 +5,7 @@
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/chromeos/ui_mode.gni")
+import("//build/config/ios/config.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//third_party/libvpx/libvpx_srcs.gni")
 import("//third_party/nasm/nasm_assemble.gni")
@@ -311,7 +312,15 @@ static_library("libvpx") {
     configs += [ "//build/config/compiler:optimize_max" ]
   }
   
-  if (is_nacl) {
+  # As "nasm" does not embed the required LC_BUILD_VERSION section in object
+  # files, it is not possible to build optimised version of the code if the
+  # target is iOS under "catalyst" environment. This version is not shipped,
+  # so there is no concern about performance.
+  # TODO(crbug.com/1145197): Remove this exception once "nasm" has support
+  # for embedding the correct LD_BUILD_VERSION section.
+  _force_generic_srcs = is_ios && target_environment == "catalyst"
+
+  if (is_nacl || _force_generic_srcs) {
     sources = libvpx_srcs_generic
   } else if (current_cpu == "x86") {
     sources = libvpx_srcs_x86
@@ -345,6 +354,7 @@ static_library("libvpx") {
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [ ":libvpx_config" ]
   deps = []
+  if (!_force_generic_srcs) {
     if (current_cpu == "x86" || (current_cpu == "x64" && !is_msan)) {
       deps += [
         ":libvpx_asm",
@@ -357,6 +367,7 @@ static_library("libvpx") {
         ":libvpx_intrinsics_ssse3",
       ]
     }
+  }
   if (cpu_arch_full == "arm-neon-cpu-detect") {
     deps += [ ":libvpx_intrinsics_neon" ]
   }