GN: Add support for 32- and 64-bit cross-compiles.

This makes it possible on Linux to refer to 64-bit targets from a 32-bit build, and 32-bit targets from a 64-bit build.

This also adds flags for Mac cross-compiles but I haven't written the toolchain definitions yet.

BUG=322106
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/81153003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236871 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 45 insertions, 15 deletions

diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index f67106b..de1ee08b 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -383,20 +383,32 @@ set_defaults("source_set") {
 # default toolchain.
 
 if (is_win) {
-  if (cpu_arch == "x64") {
+  if (build_cpu_arch == "x64") {
     host_toolchain = "//build/toolchain/win:64"
-  } else if (cpu_arch == "x86") {
+  } else if (build_cpu_arch == "x86") {
     host_toolchain = "//build/toolchain/win:32"
   }
-  set_default_toolchain(host_toolchain)
+
+  if (cpu_arch == "x64") {
+    set_default_toolchain("//build/toolchain/win:64")
+  } else if (cpu_arch == "x86") {
+    set_default_toolchain("//build/toolchain/win:32")
+  }
 } else if (is_linux) {
-  host_toolchain = "//build/toolchain/linux:host"
-  if (cpu_arch == "arm" && build_cpu_arch != "arm") {
-    # Special toolchain for ARM cross-compiling.
-    set_default_toolchain("//build/toolchain/linux:arm-cross-compile")
-  } else {
-    # Use whatever GCC is on the current platform.
-    set_default_toolchain(host_toolchain)
+  if (build_cpu_arch == "arm") {
+    host_toolchain = "//build/toolchain/linux:arm"
+  } else if (build_cpu_arch == "x86") {
+    host_toolchain = "//build/toolchain/linux:32"
+  } else if (build_cpu_arch == "x64") {
+    host_toolchain = "//build/toolchain/linux:64"
+  }
+
+  if (build_cpu_arch == "arm") {
+    set_default_toolchain("//build/toolchain/linux:arm")
+  } else if (build_cpu_arch == "x86") {
+    set_default_toolchain("//build/toolchain/linux:32")
+  } else if (build_cpu_arch == "x64") {
+    set_default_toolchain("//build/toolchain/linux:64")
   }
 } else if (is_mac) {
   host_toolchain = "//build/toolchain/mac:clang"
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 6f69e05..2ded34e 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -39,14 +39,12 @@ config("compiler") {
       cflags += [ "-fstack-protector", "--param=ssp-buffer-size=4" ]
     }
 
-    # Mac-specific compiler flags setup.
-    # ----------------------------------
     if (is_mac) {
+      # Mac-specific compiler flags setup.
+      # ----------------------------------
+
       # These flags are shared between the C compiler and linker.
       common_mac_flags = [
-        # TODO(brettw) obviously this arch flag needs to be parameterized.
-        "-arch i386",
-
         # Set which SDK to use.
         # TODO(brettw) this needs to be configurable somehow.
         "-isysroot", "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.7.sdk",
@@ -54,6 +52,13 @@ config("compiler") {
         "-mmacosx-version-min=10.6",
       ]
 
+      # CPU architecture.
+      if (cpu_arch == "x64") {
+        common_mac_flags += "-arch x86_64"
+      } else if (cpu_arch == "x32") {
+        common_mac_flags += "-arch i386"
+      }
+
       cflags += common_mac_flags + [
         # Without this, the constructors and destructors of a C++ object inside
         # an Objective C struct won't be called, which is very bad.
@@ -70,6 +75,19 @@ config("compiler") {
         "-Wl,-rpath,@loader_path/.",
         "-Wl,-rpath,@loader_path/../../..",
       ]
+    } else {
+      # Non-Mac Posix compiler flags setup.
+      # -----------------------------------
+
+      # CPU architecture. We may or may not be doing a cross compile now, so for
+      # simplicity we always explicitly set the architecture.
+      if (cpu_arch == "x64") {
+        cflags += "-m64"
+        ldflags += "-m64"
+      } else if (cpu_arch == "x32") {
+        cflags += "-m32"
+        ldflags += "-m32"
+      }
     }
 
     # Linux-specific compiler flags setup.