Start to fusl toolchain

fusl/BUILD.gn

Index: fusl/BUILD.gn
diff --git a/fusl/BUILD.gn b/fusl/BUILD.gn
index a352bcbc19e88b8e6c358b7889dbe09ab84f0390..a77d3bc05049683190cbe9cc81646f625315d8c7 100644
--- a/fusl/BUILD.gn
+++ b/fusl/BUILD.gn
@@ -2,6 +2,9 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# Define the sysroot directory.
+sysroot = "$root_out_dir/sysroot"
+
 config("fusl_config") {
   cflags = [
     # Flags from musl
@@ -1467,10 +1470,9 @@ static_library("libc") {
   deps += [ ":libc_${current_cpu}" ]
 }
 
-# Build a sysroot.
-sysroot = "${target_out_dir}/sysroot/"
-sysroot_lib_dir = "${sysroot}/usr/lib"
-sysroot_include_dir = "${sysroot}/usr/include"
+static_library("libm") {
+  complete_static_lib = true
+}
 
 template("copy_objects") {
   assert(defined(invoker.input_dir), "input_dir must be defined")
@@ -1504,6 +1506,9 @@ template("copy_objects") {
   }
 }
 
+sysroot_lib_dir = "${sysroot}/usr/lib"
+sysroot_include_dir = "${sysroot}/usr/include"
+
 copy_objects("copy_crt_objects") {
   sources = [
     "Scrt1.o",
@@ -1548,34 +1553,85 @@ copy("copy_include_bits") {
   ]
 }
 
-copy("copy_libc") {
+copy("copy_libs") {
   deps = [
     ":libc",
+    ":libm",
   ]
   sources = [
     "${target_out_dir}/libc.a",
+    "${target_out_dir}/libm.a",
   ]
   outputs = [
-    "${sysroot_lib_dir}/libc.a",
+    "${sysroot_lib_dir}/{{source_name_part}}.a",
   ]
 }
 
-group("sysroot") {
+group("copy_sysroot") {
   deps = [
     ":copy_crt_objects",
     ":copy_include",
     ":copy_include_bits",
-    ":copy_libc",
+    ":copy_libs",
   ]
   if (current_cpu == "x64") {
     deps += [ ":copy_crt_x64_objects" ]
   }
 }
 
-group("fusl") {
+# Everything that is using the fusl sysroot has a build time
+# dependency against it. However, taking an explicit dependency
+# against it will cause crt1.o and friends to be explicitly linked
+# in. This is problematic, as linkers will already by default link in
+# the correct bits of the C runtime. By adding this no-op action, we
+# preserve all the build time dependencies, but prevent crt1.o
+# etc. from ending up in downstream targets' linker response files.

[Petr Hosek, 2016/01/30 00:02:56]

That's what data_deps is for, no need for Python script or custom action.

[kulakowski, 2016/01/30 00:04:45]

There was some discussion in the mojo irc about this. It really is a build time
dependency.

The problem is that there is a transitive dependency from empty_main (my test
program) back to crt1.c, and so gn injects crt1.o into the linker script. This
then blows up with duplicate _init and _start and whatnot.

+action("sysroot") {
+  deps = [
+    ":copy_sysroot",
+  ]
+
+  script = "tools/sysroot_nothing.py"
+
+  stamp = "$target_gen_dir/sysroot_nothing.stamp"
+
+  args = [ rebase_path(stamp) ]
+
+  outputs = [
+    stamp,
+  ]
+}
+
+config("sysroot_config") {
+  rebased_sysroot = rebase_path(sysroot)
+
+  cflags = [
+    "--sysroot=$rebased_sysroot",
+    "-fPIC",
+    "-static",
+  ]
+
+  ldflags = [ "--sysroot=$rebased_sysroot" ]
+}
+
+executable("empty_main") {
+  configs = []
+  configs += [ ":sysroot_config" ]
+
+  sources = [
+    "test/empty_main.c",
+  ]
+
   deps = [
-    ":crt",
-    ":libc",
     ":sysroot",
   ]
 }
+
+group("fusl") {
+  deps = [
+    ":crt(//build/toolchain/fusl:fusl_$current_cpu)",
+    ":empty_main(//build/toolchain/fusl:fusl_$current_cpu)",
+    ":libc(//build/toolchain/fusl:fusl_$current_cpu)",
+    ":sysroot(//build/toolchain/fusl:fusl_$current_cpu)",
+  ]
+}