Make GN Android build link executables

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.
 
 # This template defines a GCC toolchain.
 #
 # It requires the following variables specifying the executables to run:
 #  - cc
 #  - cxx
 #  - ar
 #  - ld
 # and the following which is used in the toolchain_args
 #  - toolchain_cpu_arch  (What "cpu_arch" should be set to when invoking a
 #                         build using this toolchain.)
 #  - toolchain_os  (What "os" should be set to when invoking a build using this
 #                   toolchain.)
+#
+# Optional parameters:
+#  - 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.
 template("gcc_toolchain") {
   toolchain(target_name) {
     assert(defined(invoker.cc), "gcc_toolchain() must specify a \"cc\" value")
     assert(defined(invoker.cxx), "gcc_toolchain() must specify a \"cxx\" value")
     assert(defined(invoker.ar), "gcc_toolchain() must specify a \"ar\" value")
     assert(defined(invoker.ld), "gcc_toolchain() must specify a \"ld\" value")
     assert(defined(invoker.toolchain_cpu_arch),
            "gcc_toolchain() must specify a \"toolchain_cpu_arch\"")
     assert(defined(invoker.toolchain_os),
            "gcc_toolchain() must specify a \"toolchain_os\"")
 
     # We can't do string interpolation ($ in strings) on things with dots in
     # them. To allow us to use $cc below, for example, we create copies of
     # these values in our scope.
     cc = invoker.cc
     cxx = invoker.cxx
     ar = invoker.ar
     ld = invoker.ld
 
+    # Bring these into our scope for string interpolation with default values.

[awong, 2014/05/12 19:23:02]

I think we should experiment with default libs.  We should be able to avoid all
this complexity.

If you try running the gcc command with -### on both a nodefaultlib and nostdlib
configuration, I'm going to becha you'll see it "just do the right thing."

[brettw, 2014/05/12 21:00:08]

Sorry, but I am totally not touching this with a 10 ft pole.

[cjhopman, 2014/05/12 21:04:19]

Maybe we should try to do this with the gyp build since we could confirm that it
works in the different configurations (mostly just g++/clang++ and
stlport/libstdc++).

[awong, 2014/05/12 21:34:23]

Okay. I'll take this.

+    if (defined(invoker.libs_section_prefix)) {
+      libs_section_prefix = invoker.libs_section_prefix
+    } else {
+      libs_section_prefix = ""
+    }
+
+    if (defined(invoker.libs_section_postfix)) {
+      libs_section_postfix = invoker.libs_section_postfix
+    } else {
+      libs_section_postfix = ""
+    }
+
     # Make these apply to all tools below.
     lib_prefix = "-l"
     lib_dir_prefix="-L"
 
     tool("cc") {
       # cflags_pch_c
       command = "$cc -MMD -MF \$out.d \$defines \$includes \$cflags \$cflags_c -c \$in -o \$out"
       description = "CC \$out"
       depfile = "\$out.d"
       deps = "gcc"
     }
     tool("cxx") {
       # cflags_pch_cc
       command = "$cxx -MMD -MF \$out.d \$defines \$includes \$cflags \$cflags_cc -c \$in -o \$out"
       description = "CXX \$out"
       depfile = "\$out.d"
       deps = "gcc"
     }
     tool("alink") {
       command = "rm -f \$out && $ar rcs \$out \$in"
       description = "AR \$out"
     }
     tool("solink") {
-      command = "if [ ! -e \$lib -o ! -e \${lib}.TOC ]; then $ld -shared \$ldflags -o \$lib -Wl,-soname=\$soname -Wl,--whole-archive \$in \$solibs -Wl,--no-whole-archive \$libs && { readelf -d \${lib} | grep SONAME ; nm -gD -f p \${lib} | cut -f1-2 -d' '; } > \${lib}.TOC; else $ld -shared \$ldflags -o \$lib -Wl,-soname=\$soname -Wl,--whole-archive \$in \$solibs -Wl,--no-whole-archive \$libs && { readelf -d \${lib} | grep SONAME ; nm -gD -f p \${lib} | cut -f1-2 -d' '; } > \${lib}.tmp && if ! cmp -s \${lib}.tmp \${lib}.TOC; then mv \${lib}.tmp \${lib}.TOC ; fi; fi"
+      command = "if [ ! -e \$lib -o ! -e \${lib}.TOC ]; then $ld -shared \$ldflags -o \$lib -Wl,-soname=\$soname -Wl,--whole-archive \$in \$solibs -Wl,--no-whole-archive \$libs && { readelf -d \${lib} | grep SONAME ; nm -gD -f p \${lib} | cut -f1-2 -d' '; } > \${lib}.TOC; else $ld -shared \$ldflags -o \$lib -Wl,-soname=\$soname -Wl,--whole-archive \$in \$solibs -Wl,--no-whole-archive $libs_section_prefix \$libs $libs_section_postfix && { readelf -d \${lib} | grep SONAME ; nm -gD -f p \${lib} | cut -f1-2 -d' '; } > \${lib}.tmp && if ! cmp -s \${lib}.tmp \${lib}.TOC; then mv \${lib}.tmp \${lib}.TOC ; fi; fi"
       description = "SOLINK \$lib"
       #pool = "link_pool"
       restat = "1"
     }
     tool("link") {
-      command = "$ld \$ldflags -o \$out -Wl,--start-group \$in \$solibs -Wl,--end-group \$libs"
+      command = "$ld \$ldflags -o \$out -Wl,--start-group \$in \$solibs -Wl,--end-group $libs_section_prefix \$libs $libs_section_postfix"
       description = "LINK \$out"
       #pool = "link_pool"
     }
     tool("stamp") {
       command = "\${postbuilds}touch \$out"
       description = "STAMP \$out"
     }
     tool("copy") {
       command = "ln -f \$in \$out 2>/dev/null || (rm -rf \$out && cp -af \$in \$out)"
       description = "COPY \$in \$out"
     }
 
     # When invoking this toolchain not as the default one, these args will be
     # passed to the build. They are ignored when this is the default toolchain.
     toolchain_args() {
       cpu_arch = invoker.toolchain_cpu_arch
       os = invoker.toolchain_os
     }
   }
 }