[gn build] Support linux/win compiler-rt cross compilation

[aeubanks]

Summary

Right now the gn build sort of has a notion of a "host stage2" toolchain. This patch partially veers away from that and goes toward explicitly listing stage2 toolchain arch/cpu combinations.

[aeubanks]

don't use win_sysroot on win hosts

[aeubanks]

fix win build

[hans]

lgtm

llvm/utils/gn/build/toolchain/compiler.gni

17

ultra nit: line break

llvm/utils/gn/build/toolchain/BUILD.gn

 import("//llvm/utils/gn/build/toolchain/compiler.gni")
 
 declare_args() {
   # If is_goma is true, the location of the goma client install.
   # Set this to the output of `goma_ctl goma_dir`.
   goma_dir = ""
 }
 
 assert(!use_goma || goma_dir != "",
        "set `goma_dir` to the output of `goma_ctl goma_dir` in your args.gn")
 
+unix_copy_command = "ln -f {{source}} {{output}} 2>/dev/null || (rm -rf {{output}} && cp -af {{source}} {{output}})"
+
 template("unix_toolchain") {
   toolchain(target_name) {
     # https://groups.google.com/a/chromium.org/g/gn-dev/c/F_lv5T-tNDM
     forward_variables_from(invoker.toolchain_args, "*")
     not_needed("*")
 
     forward_variables_from(invoker, "*")
 
tool("link") {
       description = "LINK $outfile"
       outputs = [ outfile ]
 
       # Setting this allows targets to override the default executable output by
       # setting output_dir.
       default_output_dir = "{{root_out_dir}}/bin"
     }
 
-    copy_command = "ln -f {{source}} {{output}} 2>/dev/null || (rm -rf {{output}} && cp -af {{source}} {{output}})"
     tool("copy") {
-      command = copy_command
+      command = unix_copy_command
       description = "COPY {{source}} {{output}}"
     }
 
     if (current_os == "ios" || current_os == "mac") {
       tool("copy_bundle_data") {
         # https://github.com/nico/hack/blob/master/notes/copydir.md
         _copydir = "cd {{source}} && " +
                    "find . | cpio -pdl \"\$OLDPWD\"/{{output}} 2>/dev/null"
tool("link") {
       default_output_extension = ".exe"
 
       # Setting this allows targets to override the default executable output by
       # setting output_dir.
       default_output_dir = "{{root_out_dir}}/bin"
     }
 
     tool("copy") {
+      if (host_os == "win") {
         # GN hands out slash-using paths, but cmd's copy needs backslashes.
         # Use cmd's %foo:a=b% substitution feature to convert.
         command = "cmd /c set source=\"{{source}}\" & set output=\"{{output}}\" & call copy /Y %source:/=\% %output:\=/% > nul"
+      } else {
+        command = unix_copy_command
+      }
+
       description = "COPY {{source}} {{output}}"
     }
 
     tool("stamp") {
+      if (host_os == "win") {
         command = "cmd /c type nul > {{output}}"
+      } else {
+        command = "touch {{output}}"
+      }
       description = "STAMP {{output}}"
     }
   }
 }
 
 win_toolchain("win") {
   toolchain_args = {
     current_os = "win"
     current_cpu = host_cpu
   }
 }
 
-win_toolchain("stage2_win") {
+win_toolchain("stage2_win_x64") {
   toolchain_args = {
-    current_os = host_os
-    current_cpu = host_cpu
+    current_os = "win"
+    current_cpu = "x64"
 
+    if (host_os != "win") {
+      sysroot = win_sysroot
+    }
     clang_base_path = root_build_dir
     use_goma = false
   }
   deps = [
     "//:clang($host_toolchain)",
     "//:lld($host_toolchain)",
   ]
 }
 
 win_toolchain("stage2_win_x86") {
   toolchain_args = {
-    current_os = host_os
+    current_os = "win"
     current_cpu = "x86"
 
+    if (host_os != "win") {
+      sysroot = win_sysroot
+    }
     clang_base_path = root_build_dir
     use_goma = false
   }
   deps = [
     "//:clang($host_toolchain)",
     "//:lld($host_toolchain)",
   ]
 }

llvm/utils/gn/build/toolchain/compiler.gni

 declare_args() {
   # Whether to use goma (https://chromium.googlesource.com/infra/goma/client/)
   use_goma = false
 
   # Set this to a clang build directory. If set, that clang is used as compiler.
   # goma only works with compiler binaries it knows about, so useful both for
   # using a goma-approved compiler and for compiling clang with a locally-built
   # clang in a different build directory.
   # On Windows, setting this also causes lld-link to be used as linker.
   # Example value: getenv("HOME") + "/src/llvm-build/Release+Asserts"
   clang_base_path = ""
 
   # Set this to the path to Android NDK r21. If set, cross compilation targeting
   # Android will be enabled.
   android_ndk_path = ""
+
+  # Set this to the path of the Win SDK. Only used for cross compilation. If set, cross compilation targeting Windows will be enabled.
+  win_sysroot = ""
 }
 
 declare_args() {
   # Set if the host compiler is clang.  On by default on Mac or if
   # clang_base_path is set.
   is_clang = host_os == "mac" || clang_base_path != ""
 
   # Set this to true to link with LLD instead of the default linker.
   use_lld = clang_base_path != ""
 }
+
+assert(
+    !(host_os == "win" && win_sysroot != ""),
+    "win_sysroot should only be used for cross compilation, use sysroot on Windows")

llvm/utils/gn/build/toolchain/target_flags.gni

target_ldflags += [
       "x86_64",
     ]
   }
 } else if (current_os == "baremetal") {
   target_flags += [ "--target=$llvm_current_triple" ]
 }
 
 if (current_cpu == "x86") {
-  target_flags = [ "-m32" ]
+  target_flags += [ "-m32" ]
 }

llvm/utils/gn/secondary/compiler-rt/BUILD.gn

 import("//llvm/lib/Target/targets.gni")
 import("//llvm/utils/gn/build/mac_sdk.gni")
 import("//llvm/utils/gn/build/toolchain/compiler.gni")
 
 # In the GN build, compiler-rt is always built by just-built clang and lld.
 # FIXME: For macOS and iOS builds, depend on lib in all needed target arch
 # toolchains and then lipo them together for the final output.
-if (current_os == "win") {
-  supported_toolchains = [ "//llvm/utils/gn/build/toolchain:stage2_win" ]
+supported_toolchains = []
+if (host_os == "win" || win_sysroot != "") {
+  supported_toolchains += [ "//llvm/utils/gn/build/toolchain:stage2_win_x64" ]
   supported_toolchains += [ "//llvm/utils/gn/build/toolchain:stage2_win_x86" ]
-} else {
-  supported_toolchains = [ "//llvm/utils/gn/build/toolchain:stage2_unix" ]
+}
+if (host_os != "win") {
+  supported_toolchains += [ "//llvm/utils/gn/build/toolchain:stage2_unix" ]
 }
 supported_toolchains += supported_android_toolchains
 if (llvm_build_AArch64) {
   supported_toolchains +=
       [ "//llvm/utils/gn/build/toolchain:stage2_baremetal_aarch64" ]
 }
 group("compiler-rt") {
   deps = [ "//compiler-rt/include($host_toolchain)" ]

llvm/utils/gn/secondary/compiler-rt/test/asan/BUILD.gn

group("asan_toolchain") {
     ]
   }
 }
 
 supported_toolchains = []
 if (host_os == "linux") {
   supported_toolchains += [ "//llvm/utils/gn/build/toolchain:stage2_unix" ]
 } else if (host_os == "win") {
-  supported_toolchains += [ "//llvm/utils/gn/build/toolchain:stage2_win" ]
+  supported_toolchains += [ "//llvm/utils/gn/build/toolchain:stage2_win_x64" ]
 }
+
 group("asan") {
   deps = []
   foreach(toolchain, supported_toolchains) {
     deps += [ ":asan_toolchain($toolchain)" ]
   }
 }
 
 if (supported_toolchains != []) {