For building v8 using gn on aix_ppc64, linux_s390x and linux_ppc64.

build/config/BUILDCONFIG.gn

Index: build/config/BUILDCONFIG.gn
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index d055e705627c96782434537d0157594ff4f6dad0..1bbdb5f766d69ea1ecf3214f523933bb822fb1e1 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -69,6 +69,22 @@ if (current_os == "") {
   current_os = target_os
 }
 
+# Detect host byteorder
+# ppc64 can be either BE or LE
+if (host_cpu == "ppc64") {
+  if (current_os == "aix") {
+    host_byteorder = "big"
+  } else {
+    # Only use the script when absolutely necessary
+    host_byteorder = exec_script("//build/get_byteorder.py", [], "trim string")

[Dirk Pranke, 2017/04/14 01:32:38]

Maybe we should make host_byteorder a built in variable (like host_cpu) instead?

[Dirk Pranke, 2017/04/18 20:31:31]

I've changed my mind. To repeat my latest comment from the v8-side patch:

I think we should leave this here, at least until we have a need for
host_byteorder somewhere outside of v8.

If we have that need at that time, we should start by creating a separate
host_byteorder.gni file, rather than setting it in BUILDCONFIG. We should avoid
changes to BUILDCONFIG if at all possible.

[rayb, 2017/04/25 00:41:03]

using host_byteorder.gni now.

+  }
+} else if (host_cpu == "ppc" || host_cpu == "s390" || host_cpu == "s390x" ||
+           host_cpu == "mips" || host_cpu == "mips64") {
+  host_byteorder = "big"
+} else {
+  host_byteorder = "little"
+}
+
 # =============================================================================
 # BUILD FLAGS
 # =============================================================================
@@ -136,7 +152,10 @@ declare_args() {
   # Set to true when compiling with the Clang compiler. Typically this is used
   # to configure warnings.
   is_clang = current_os == "mac" || current_os == "ios" ||
-             current_os == "linux" || current_os == "chromeos"
+             (current_os == "linux" &&
+              (current_cpu != "s390x" && current_cpu != "s390" &&
+               current_cpu != "ppc64" && current_cpu != "ppc")) ||
+             current_os == "chromeos"

[Michael Achenbach, 2017/04/18 13:46:03]

nit: Maybe move the chromeos clause before the linux clause for readability (to
have the most complicated clause last)? Not sure what formatting does to it
though...

[rayb, 2017/04/25 00:41:03]

Done.

 
   # Allows the path to a custom target toolchain to be injected as a single
   # argument, and set as the default toolchain.
@@ -207,6 +226,8 @@ if (host_toolchain == "") {
     } else {
       host_toolchain = "//build/toolchain/win:$target_cpu"
     }
+  } else if (host_os == "aix") {
+    host_toolchain = "//build/toolchain/aix:$host_cpu"
   } else {
     assert(false, "Unsupported host_os: $host_os")
   }
@@ -242,6 +263,8 @@ if (target_os == "android") {
   } else {
     _default_toolchain = "//build/toolchain/win:$target_cpu"
   }
+} else if (target_os == "aix") {
+  _default_toolchain = "//build/toolchain/aix:$target_cpu"
 } else if (target_os == "winrt_81" || target_os == "winrt_81_phone" ||
            target_os == "winrt_10") {
   _default_toolchain = "//build/toolchain/win:winrt_$target_cpu"
@@ -342,6 +365,15 @@ if (current_os == "win" || current_os == "winrt_81" ||
   is_nacl = false
   is_posix = true
   is_win = false
+} else if (current_os == "aix") {
+  is_android = false
+  is_chromeos = false
+  is_ios = false
+  is_linux = false
+  is_mac = false
+  is_nacl = false
+  is_posix = true
+  is_win = false
 }
 
 # =============================================================================
@@ -370,6 +402,7 @@ if (!is_posix) {
     "*\bposix/*",
   ]
 }
+
 if (!is_win) {
   sources_assignment_filter += [
     "*_win.cc",
@@ -498,11 +531,13 @@ if (current_os == "winrt_81" || current_os == "winrt_81_phone" ||
     current_os == "winrt_10") {
   default_compiler_configs += [ "//build/config/win:target_winrt" ]
 }
+
 if (is_posix) {
-  default_compiler_configs += [
-    "//build/config/gcc:no_exceptions",
-    "//build/config/gcc:symbol_visibility_hidden",
-  ]
+  default_compiler_configs += [ "//build/config/gcc:no_exceptions" ]
+  if (current_os != "aix") {
+    default_compiler_configs +=
+        [ "//build/config/gcc:symbol_visibility_hidden" ]
+  }
 }
 
 if (is_android) {