# HG changeset patch
# User Dan Minor <dminor@mozilla.com>
# Date 1556723088 0
# Node ID f1bc4fcd152e66e858c3a1d0b0afd30a78e9474b
# Parent  c25bb3353335741cf7045c4430ea4c8c33f6f074
Bug 1540760 - Make it possible to use clang-cl as an assembler; r=firefox-build-system-reviewers,mshal

Some media libraries use gas syntax in their assembly files. Rather than
converting these arm assembly syntax files for aarch64, we can use clang-cl
to build them directly.

Differential Revision: https://phabricator.services.mozilla.com/D27785

diff --git a/build/moz.configure/toolchain.configure b/build/moz.configure/toolchain.configure
--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -2110,16 +2110,30 @@ def have_yasm(yasm_asflags):
         return True
 
 set_config('HAVE_NASM', have_nasm)
 
 set_config('HAVE_YASM', have_yasm)
 # Until the YASM variable is not necessary in old-configure.
 add_old_configure_assignment('YASM', have_yasm)
 
+
+# clang-cl integrated assembler support
+# ==============================================================
+@depends(target)
+def clangcl_asflags(target):
+    asflags = None
+    if target.os == 'WINNT' and target.cpu == 'aarch64':
+        asflags = ['--target=aarch64-windows-msvc']
+    return asflags
+
+
+set_config('CLANGCL_ASFLAGS', clangcl_asflags)
+
+
 # Code Coverage
 # ==============================================================
 
 js_option('--enable-coverage', env='MOZ_CODE_COVERAGE',
           help='Enable code coverage')
 
 @depends('--enable-coverage')
 def code_coverage(value):
diff --git a/python/mozbuild/mozbuild/frontend/context.py b/python/mozbuild/mozbuild/frontend/context.py
--- a/python/mozbuild/mozbuild/frontend/context.py
+++ b/python/mozbuild/mozbuild/frontend/context.py
@@ -2195,16 +2195,24 @@ VARIABLES = {
 
         By default, the build will use the toolchain assembler, $(AS), to
         assemble source files in assembly language (.s or .asm files). Setting
         this value to ``True`` will cause it to use yasm instead.
 
         If yasm is not available on this system, or does not support the
         current target architecture, an error will be raised.
         """),
+
+    'USE_INTEGRATED_CLANGCL_AS': (bool, bool,
+        """Use the integrated clang-cl assembler to assemble assembly files from SOURCES.
+
+        This allows using clang-cl to assemble assembly files which is useful
+        on platforms like aarch64 where the alternative is to have to run a
+        pre-processor to generate files with suitable syntax.
+        """),
 }
 
 # Sanity check: we don't want any variable above to have a list as storage type.
 for name, (storage_type, input_types, docs) in VARIABLES.items():
     if storage_type == list:
         raise RuntimeError('%s has a "list" storage type. Use "List" instead.'
             % name)
 
diff --git a/python/mozbuild/mozbuild/frontend/emitter.py b/python/mozbuild/mozbuild/frontend/emitter.py
--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -1353,16 +1353,26 @@ class TreeMetadataEmitter(LoggingMixin):
             if not nasm:
                 raise SandboxValidationError('nasm is not available', context)
             passthru.variables['AS'] = nasm
             passthru.variables['AS_DASH_C_FLAG'] = ''
             passthru.variables['ASOUTOPTION'] = '-o '
             computed_as_flags.resolve_flags('OS',
                                             context.config.substs.get('NASM_ASFLAGS', []))
 
+        if context.get('USE_INTEGRATED_CLANGCL_AS') is True:
+            clangcl = context.config.substs.get('CLANG_CL')
+            if not clangcl:
+                raise SandboxValidationError('clang-cl is not available', context)
+            passthru.variables['AS'] = 'clang-cl'
+            passthru.variables['AS_DASH_C_FLAG'] = '-c'
+            passthru.variables['ASOUTOPTION'] = '-o '
+            computed_as_flags.resolve_flags('OS',
+                                            context.config.substs.get('CLANGCL_ASFLAGS', []))
+
         if passthru.variables:
             yield passthru
 
         if context.objdir in self._compile_dirs:
             self._compile_flags[context.objdir] = computed_flags
             yield computed_link_flags
 
         if context.objdir in self._asm_compile_dirs: