Rework the way ChromiumOS toolchains will work in GN.

build/toolchain/gcc_toolchain.gni

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/nacl/config.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
 
@@ skipping 16 matching lines @@
 #  - ar
 #  - ld
 # and the following which is used in the toolchain_args
 #  - toolchain_cpu  (What "current_cpu" should be set to when invoking a
 #                    build using this toolchain.)
 #  - toolchain_os  (What "current_os" should be set to when invoking a
 #                   build using this toolchain.)
 #
 # Optional parameters that control the tools:
 #
+#  - extra_cflags
+#      Extra flags to be appended when compiling C files
+#  - extra_cppflags

[hashimoto, 2016/05/17 06:26:31]

nit: It'd be nice to make it clear the difference between this and
extra_cxxflags. People may think cpp stands for c-plus-plus.

[Dirk Pranke, 2016/05/17 21:37:45]

Will add comments.

+#      Extra flags to be appended when compiling C or C++ files
+#  - extra_cxxflags
+#      Extra flags to be appended when compiling C or C++ files

[hashimoto, 2016/05/17 06:26:31]

nit: Not when compiling C?

[Dirk Pranke, 2016/05/17 21:37:45]

Whoops. Will fix.

+#  - extra_ldflags
+#      Extra flags to be appended when linking
+#
 #  - libs_section_prefix
 #  - libs_section_postfix
 #      The contents of these strings, if specified, will be placed around
 #      the libs section of the linker line. It allows one to inject libraries
 #      at the beginning and end for all targets in a toolchain.
 #  - solink_libs_section_prefix
 #  - solink_libs_section_postfix
 #      Same as libs_section_{pre,post}fix except used for solink instead of link.
 #  - link_outputs
 #      The content of this array, if specified, will be added to the list of
@@ skipping 126 matching lines @@
     } else {
       solink_libs_section_prefix = ""
     }
 
     if (defined(invoker.solink_libs_section_postfix)) {
       solink_libs_section_postfix = invoker.solink_libs_section_postfix
     } else {
       solink_libs_section_postfix = ""
     }
 
+    if (defined(invoker.extra_cflags) && invoker.extra_cflags != "") {
+      extra_cflags = " " + invoker.extra_cflags
+    } else {
+      extra_cflags = ""
+    }
+
+    if (defined(invoker.extra_cppflags) && invoker.extra_cppflags != "") {
+      extra_cppflags = " " + invoker.extra_cppflags
+    } else {
+      extra_cppflags = ""
+    }
+
+    if (defined(invoker.extra_cxxflags) && invoker.extra_cxxflags != "") {
+      extra_cxxflags = " " + invoker.extra_cxxflags
+    } else {
+      extra_cxxflags = ""
+    }
+
+    if (defined(invoker.extra_ldflags) && invoker.extra_ldflags != "") {
+      extra_ldflags = " " + invoker.extra_ldflags
+    } else {
+      extra_ldflags = ""
+    }
+
     # These library switches can apply to all tools below.
     lib_switch = "-l"
     lib_dir_switch = "-L"
 
     # Object files go in this directory.
     object_subdir = "{{target_out_dir}}/{{label_name}}"
 
     tool("cc") {
       depfile = "{{output}}.d"
-      command = "$cc -MMD -MF $depfile ${rebuild_string}{{defines}} {{include_dirs}} {{cflags}} {{cflags_c}} -c {{source}} -o {{output}}"
+      command = "$cc -MMD -MF $depfile ${rebuild_string}{{defines}} {{include_dirs}} {{cflags}} {{cflags_c}}${extra_cppflags}${extra_cflags} -c {{source}} -o {{output}}"
       depsformat = "gcc"
       description = "CC {{output}}"
       outputs = [
         "$object_subdir/{{source_name_part}}.o",
       ]
     }
 
     tool("cxx") {
       depfile = "{{output}}.d"
-      command = "$cxx -MMD -MF $depfile ${rebuild_string}{{defines}} {{include_dirs}} {{cflags}} {{cflags_cc}} -c {{source}} -o {{output}}"
+      command = "$cxx -MMD -MF $depfile ${rebuild_string}{{defines}} {{include_dirs}} {{cflags}} {{cflags_cc}}${extra_cppflags}${extra_cxxflags} -c {{source}} -o {{output}}"
       depsformat = "gcc"
       description = "CXX {{output}}"
       outputs = [
         "$object_subdir/{{source_name_part}}.o",
       ]
     }
 
     tool("asm") {
       # For GCC we can just use the C compiler to compile assembly.
       depfile = "{{output}}.d"
@@ skipping 37 matching lines @@
       } else {
         unstripped_sofile = sofile
       }
 
       # These variables are not built into GN but are helpers that
       # implement (1) linking to produce a .so, (2) extracting the symbols
       # from that file (3) if the extracted list differs from the existing
       # .TOC file, overwrite it, otherwise, don't change it.
       tocfile = sofile + ".TOC"
 
-      link_command = "$ld -shared {{ldflags}} -o \"$unstripped_sofile\" -Wl,-soname=\"$soname\" @\"$rspfile\""
+      link_command = "$ld -shared {{ldflags}}${extra_ldflags} -o \"$unstripped_sofile\" -Wl,-soname=\"$soname\" @\"$rspfile\""
 
       assert(defined(readelf), "to solink you must have a readelf")
       assert(defined(nm), "to solink you must have an nm")
       strip_switch = ""
       if (defined(invoker.strip)) {
         strip_switch = "--strip=${invoker.strip}"
       }
 
       # This needs a Python script to avoid using a complex shell command
       # requiring sh control structures, pipelines, and POSIX utilities.
@@ skipping 39 matching lines @@
       soname = "{{target_output_name}}{{output_extension}}"  # e.g. "libfoo.so".
       sofile = "{{output_dir}}/$soname"
       rspfile = sofile + ".rsp"
 
       if (defined(invoker.strip)) {
         unstripped_sofile = "{{root_out_dir}}/lib.unstripped/$soname"
       } else {
         unstripped_sofile = sofile
       }
 
-      command = "$ld -shared {{ldflags}} -o \"$unstripped_sofile\" -Wl,-soname=\"$soname\" @\"$rspfile\""
+      command = "$ld -shared {{ldflags}}${extra_ldflags} -o \"$unstripped_sofile\" -Wl,-soname=\"$soname\" @\"$rspfile\""
 
       if (defined(invoker.strip)) {
         strip_command = "${invoker.strip} --strip-unneeded -o \"$sofile\" \"$unstripped_sofile\""
         command += " && " + strip_command
       }
       rspfile_content = "-Wl,--whole-archive {{inputs}} {{solibs}} -Wl,--no-whole-archive $solink_libs_section_prefix {{libs}} $solink_libs_section_postfix"
 
       description = "SOLINK_MODULE $sofile"
 
       # Use this for {{output_extension}} expansions unless a target manually
@@ skipping 30 matching lines @@
       # overrides it (in which case {{output_extension}} will be what the target
       # specifies).
       default_output_extension = default_executable_extension
 
       default_output_dir = "{{root_out_dir}}"
 
       if (defined(invoker.strip)) {
         unstripped_outfile = "{{root_out_dir}}/exe.unstripped/$exename"
       }
 
-      command = "$ld {{ldflags}} -o \"$unstripped_outfile\" -Wl,--start-group @\"$rspfile\" {{solibs}} -Wl,--end-group $libs_section_prefix {{libs}} $libs_section_postfix"
+      command = "$ld {{ldflags}}${extra_ldflags} -o \"$unstripped_outfile\" -Wl,--start-group @\"$rspfile\" {{solibs}} -Wl,--end-group $libs_section_prefix {{libs}} $libs_section_postfix"
       if (defined(invoker.strip)) {
         link_wrapper =
             rebase_path("//build/toolchain/gcc_link_wrapper.py", root_build_dir)
         command = "$python_path \"$link_wrapper\" --strip=\"${invoker.strip}\" --unstripped-file=\"$unstripped_outfile\" --output=\"$outfile\" -- $command"
       }
       description = "LINK $outfile"
       rspfile_content = "{{inputs}}"
       outputs = [
         outfile,
       ]
@@ skipping 39 matching lines @@
       }
       if (defined(invoker.symbol_level)) {
         symbol_level = invoker.symbol_level
       }
       if (defined(invoker.use_allocator)) {
         use_allocator = invoker.use_allocator
       }
       if (defined(invoker.use_gold)) {
         use_gold = invoker.use_gold
       }
+      if (defined(invoker.use_sysroot)) {
+        use_sysroot = invoker.use_sysroot

[hashimoto, 2016/05/17 06:26:31]

Sorry, I'm not familiar enough with GN to understand this code.
Does this mean the global use_sysroot (i.e. the one in args.gn) is hidden by
this local use_sysroot when using this toolchain?

[Dirk Pranke, 2016/05/17 21:37:45]

Yes, exactly. 

See
https://chromium.googlesource.com/chromium/src/+/master/tools/gn/docs/referen...
 (`gn help toolchain` and `gn help toolchain_args`). Basically these variables
will override the ones that are set globally in args.gn (or have the default
values) *for targets using that toolchain*.

+      }
 
       if (defined(invoker.clear_sanitizers) && invoker.clear_sanitizers) {
         is_asan = false
         is_cfi = false
         is_lsan = false
         is_msan = false
         is_syzyasan = false
         is_tsan = false
         is_ubsan = false
         is_ubsan_vptr = false
@@ skipping 36 matching lines @@
 
     forward_variables_from(invoker,
                            [
                              "toolchain_cpu",
                              "toolchain_os",
                              "use_gold",
                              "strip",
                            ])
   }
 }