NOT FOR REVIEW: proof-of-concept for building lib/linux/libclang_rt.profile-x86_64.a on a mac in the gn build

[thakis]

Summary

Seems to work!

Hardcodes the path to the linux sysroot, so not landable as-is.

[dblaikie]

If you create a review using arc's --draft (I think that's the name/spelling) it'll avoid sending email to the *-dev list, so you can create it and share it around without adding more email to the busy *-dev lists until you're ready to send it for review, btw.

[thakis]

In D104466#2831949, @dblaikie wrote:

If you create a review using arc's --draft (I think that's the name/spelling) it'll avoid sending email to the *-dev list, so you can create it and share it around without adding more email to the busy *-dev lists until you're ready to send it for review, btw.

I don't use arc. It has a bunch of dependencies that make it difficult to use on non-linux. (But if there's a way to create drafts in the web ui, lmk and I'll use that.)

[dblaikie]

In D104466#2860607, @thakis wrote:

In D104466#2831949, @dblaikie wrote:

If you create a review using arc's --draft (I think that's the name/spelling) it'll avoid sending email to the *-dev list, so you can create it and share it around without adding more email to the busy *-dev lists until you're ready to send it for review, btw.

I don't use arc. It has a bunch of dependencies that make it difficult to use on non-linux. (But if there's a way to create drafts in the web ui, lmk and I'll use that.)

Yeah, fair for sure - @MaskRay / @mehdi_amini - any ideas how to do this directly in the web UI, perhaps?

[MaskRay]

arc diff --draft 'HEAD^' triggers build bots but doesn't trigger llvm-commits subscription.

[dblaikie]

In D104466#2860632, @MaskRay wrote:

arc diff --draft 'HEAD^' triggers build bots but doesn't trigger llvm-commits subscription.

Is there a way to do it without arc, though? (where it might be difficult to get/use arc on some platforms, etc)

llvm/utils/gn/build/BUILD.gn

if (host_os != "win") {
     ]
     cflags += [ "/EHs-c-" ]
 
     # The MSVC default value (1 MB) is not enough for parsing recursive C++
     # templates in Clang.
     ldflags += [ "/STACK:10000000" ]
   }
 
+  if (host_os != current_os && !(host_os == "mac" && current_os == "ios")) {
+    if (current_os == "linux" && current_cpu == "x64") {
+      cflags += [ "--target=x86_64-linux-gnu" ]
+    } else {
+      assert(false, "unimplemented cross config $host_os => $current_os")
+    }
+  }
+
   # Warning setup.
   if (host_os == "win" && !is_clang) {
     cflags += [
       # Suppress ''modifier' : used more than once' (__forceinline and inline).
       "-wd4141",
 
       # Suppress 'conversion from 'type1' to 'type2', possible loss of data'.
       "-wd4244",

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

toolchain_args = {
       clang_base_path = root_build_dir
       use_goma = false
     }
 
     deps = [
       "//:clang($host_toolchain)",
       "//:lld($host_toolchain)",
     ]
-    if (current_os != "ios" && current_os != "mac") {
+    if (toolchain_args.current_os != "ios" && toolchain_args.current_os != "mac") {
       ar = "bin/llvm-ar"
       deps += [ "//:llvm-ar($host_toolchain)" ]
     }
   }
 }
 
 stage2_unix_toolchain("stage2_unix") {
   toolchain_args = {
     current_os = host_os
     current_cpu = host_cpu
   }
 }
 
+stage2_unix_toolchain("stage2_unix_linux") {
+  toolchain_args = {
+    current_os = "linux"
+    current_cpu = host_cpu
+    sysroot = "//sysroot-linux"
+  }
+}
+
 if (android_ndk_path != "") {
   stage2_unix_toolchain("stage2_android_aarch64") {
     toolchain_args = {
       current_os = "android"
       current_cpu = "arm64"
     }
   }
 

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" ]
 } else {
   supported_toolchains = [ "//llvm/utils/gn/build/toolchain:stage2_unix" ]
 }
+if (current_os == "mac") {
+  supported_toolchains += [ "//llvm/utils/gn/build/toolchain:stage2_unix_linux" ]
+}
 if (android_ndk_path != "") {
   supported_toolchains += [
     "//llvm/utils/gn/build/toolchain:stage2_android_aarch64",
     "//llvm/utils/gn/build/toolchain:stage2_android_arm",
   ]
 }
 group("compiler-rt") {
   deps = []