clang build script: scale back xcode stuff a bit

Hopefully still enough to have an arm64 compiler-rt while keeping the
rest of the script mostly as it was before
https://chromium-review.googlesource.com/c/chromium/src/+/2269512

Bug: 1098899
Change-Id: I67385083126d2d1e75599b0bd201e8bc9894809b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2274590Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784023}

tools/clang/scripts/build.py

@@ -455,33 +455,8 @@ def main():
   # enough GCC to build Clang.
   MaybeDownloadHostGcc(args)
 
-  # mac/arm64 needs MacOSX11.0.sdk. System Xcode (+ SDK) on the chrome bots
-  # is something much older.
-  # Options:
-  # - temporarily set system Xcode to Xcode 12 beta while running this script,
-  #   (cf build/swarming_xcode_install.py, but it looks unused)
-  # - use Xcode 12 beta for everything on tot bots, only need to fuzz with
-  #   scripts/slave/recipes/chromium_upload_clang.py then (but now the
-  #   chrome/ios build will use the 11.0 SDK too and we'd be on the hook for
-  #   keeping it green -- if it's currently green, who knows)
-  # - pass flags to cmake to try to coax it into using Xcode 12 beta for the
-  #   LLVM build without it being system Xcode.
-  #
-  # The last option seems best, so let's go with that. We need to pass
-  # -isysroot to the 11.0 SDK and -B to the /usr/bin so that the new ld64 is
-  # used.
   if sys.platform == 'darwin':
     isysroot = subprocess.check_output(['xcrun', '--show-sdk-path']).rstrip()
-  if sys.platform == 'darwin' and args.bootstrap:
-    sys.path.insert(1, os.path.join(CHROMIUM_DIR, 'build'))
-    import mac_toolchain
-    LLVM_XCODE = os.path.join(THIRD_PARTY_DIR, 'llvm-xcode')
-    mac_toolchain.InstallXcodeBinaries('xcode_12_beta', LLVM_XCODE)
-    isysroot = os.path.join(LLVM_XCODE, 'Contents', 'Developer', 'Platforms',
-                            'MacOSX.platform', 'Developer', 'SDKs',
-                            'MacOSX11.0.sdk')
-    xcode_bin = os.path.join(LLVM_XCODE, 'Contents', 'Developer', 'Toolchains',
-                             'XcodeDefault.xctoolchain', 'usr', 'bin')
 
   global CLANG_REVISION, PACKAGE_VERSION
   if args.llvm_force_head_revision:
@@ -748,7 +723,6 @@ def main():
                 '-target', 'x86_64-unknown-unknown', '-O2', '-g', '-std=c++14',
                  '-fno-exceptions', '-fno-rtti', '-w', '-c', training_source]
     if sys.platform == 'darwin':
-      # TODO(thakis): Try switching tihs back to `xcrun --show-sdk-path`.
       train_cmd.extend(['-stdlib=libc++', '-isysroot', isysroot])
     RunCommand(train_cmd, msvc_arch='x64')
 
@@ -778,14 +752,42 @@ def main():
         '-DDARWIN_iossim_ARCHS=i386;x86_64',
         ])
     if args.bootstrap:
+      # mac/arm64 needs MacOSX11.0.sdk. System Xcode (+ SDK) on the chrome bots
+      # is something much older.
+      # Options:
+      # - temporarily set system Xcode to Xcode 12 beta while running this
+      #   script, (cf build/swarming_xcode_install.py, but it looks unused)
+      # - use Xcode 12 beta for everything on tot bots, only need to fuzz with
+      #   scripts/slave/recipes/chromium_upload_clang.py then (but now the
+      #   chrome/ios build will use the 11.0 SDK too and we'd be on the hook for
+      #   keeping it green -- if it's currently green, who knows)
+      # - pass flags to cmake to try to coax it into using Xcode 12 beta for the
+      #   LLVM build without it being system Xcode.
+      #
+      # The last option seems best, so let's go with that. We need to pass
+      # -isysroot to the 11.0 SDK and -B to the /usr/bin so that the new ld64 is
+      # used.
+      # The compiler-rt build overrides -isysroot flags set via cflags, and we
+      # only need to use the 11 SDK for the compiler-rt build. So set only
+      # DARWIN_macosx_CACHED_SYSROOT to the 11.0 SDK and use the regular SDK
+      # for the rest of the build. (The new ld is used for all links.)
+      sys.path.insert(1, os.path.join(CHROMIUM_DIR, 'build'))
+      import mac_toolchain
+      LLVM_XCODE = os.path.join(THIRD_PARTY_DIR, 'llvm-xcode')
+      mac_toolchain.InstallXcodeBinaries('xcode_12_beta', LLVM_XCODE)
+      isysroot_11 = os.path.join(LLVM_XCODE, 'Contents', 'Developer',
+                                 'Platforms', 'MacOSX.platform', 'Developer',
+                                 'SDKs', 'MacOSX11.0.sdk')
+      xcode_bin = os.path.join(LLVM_XCODE, 'Contents', 'Developer',
+                               'Toolchains', 'XcodeDefault.xctoolchain', 'usr',
+                               'bin')
       # Include an arm64 slice for libclang_rt.osx.a. This requires using
       # MacOSX11.0.sdk (via -isysroot, via DARWIN_macosx_CACHED_SYSROOT) and
       # the new ld, via -B
       compiler_rt_args.extend([
           # We don't need 32-bit intel support for macOS, we only ship 64-bit.
-          # XXX probably only add arm64 for bootstrap builds
           '-DDARWIN_osx_ARCHS=arm64;x86_64',
-          '-DDARWIN_macosx_CACHED_SYSROOT=' + isysroot,
+          '-DDARWIN_macosx_CACHED_SYSROOT=' + isysroot_11,
       ])
       ldflags += ['-B', xcode_bin]
     else:
@@ -802,7 +804,6 @@ def main():
   if sys.platform == 'darwin' and args.bootstrap:
     # When building on 10.9, /usr/include usually doesn't exist, and while
     # Xcode's clang automatically sets a sysroot, self-built clangs don't.
-    # TODO(thakis): Try changing this back to `xcrun --show-sdk-path`.
     cflags = ['-isysroot', isysroot]
     cxxflags = ['-stdlib=libc++'] + cflags
     ldflags += ['-stdlib=libc++']

tools/clang/scripts/update.py

@@ -39,7 +39,7 @@ import zipfile
 # Reverting problematic clang rolls is safe, though.
 CLANG_REVISION = 'fb1aa286c1400ad7'
 CLANG_SVN_REVISION = 'n358615'
-CLANG_SUB_REVISION = 2
+CLANG_SUB_REVISION = 3
 
 PACKAGE_VERSION = '%s-%s-%s' % (CLANG_SVN_REVISION, CLANG_REVISION[:8],
                                 CLANG_SUB_REVISION)