[MIPS] Implementation of sel_ldr for MIPS architecture.

SConstruct

Index: SConstruct
diff --git a/SConstruct b/SConstruct
index faca3da3ae369a7c46b03a31e255dbf4b52c75e8..7a9d7aeeb06d8a3fee592d17785a73b116816c47 100755
--- a/SConstruct
+++ b/SConstruct
@@ -2259,6 +2259,37 @@ def SetupLinuxEnvArm(env):
   # get_plugin_dirname.cc has a dependency on dladdr
   env.Append(LIBS=['dl'])
 
+def SetupLinuxEnvMips(env):
+  jail = '${SCONSTRUCT_DIR}/toolchain/linux_mips-trusted'
+  if env.Bit('built_elsewhere'):
+    def FakeInstall(dest, source, env):
+      print 'Not installing', dest
+      # Replace build commands with no-ops
+    env.Replace(CC='true', CXX='true', LD='true',
+                AR='true', RANLIB='true', INSTALL=FakeInstall)
+    # Allow emulation on x86 hosts for testing built_elsewhere flag
+    if not platform.machine().startswith('mips'):
+      env.Replace(EMULATOR=jail + '/run_under_qemu_mips32')
+  else:
+    sys.path.append('tools/trusted_cross_toolchains')
+    from setup_mips32_trusted_toolchain import mips32_env
+    sys.path.pop()
+    # Allow env vars to override these settings, for what it's worth.
+    mips32_env = mips32_env.copy()
+    mips32_env.update(os.environ)
+    env.Replace(CC=mips32_env.get('MIPS32_CC', 'NO-MIPSEL-CC-SPECIFIED'),
+                CXX=mips32_env.get('MIPS32_CXX', 'NO-MIPSEL-CXX-SPECIFIED'),
+                LD=mips32_env.get('MIPS32_LD', 'NO-MIPSEL-LD-SPECIFIED'),
+                EMULATOR=mips32_env.get('MIPS32_EMU', ''),
+                ASFLAGS=[],
+                LIBPATH=['${LIB_DIR}',
+                mips32_env.get('MIPS32_LIB_DIR', '').split()],
+                LINKFLAGS=mips32_env.get('MIPS32_LINKFLAGS', ''),
+                )
+
+    env.Append(LIBS=['rt', 'dl', 'pthread'],
+                     CCFLAGS=['-EL', '-Wl,-EL', '-march=mips32r2'])
+
 def MakeLinuxEnv():
   linux_env = MakeUnixLikeEnv().Clone(
       BUILD_TYPE = '${OPTIMIZATION_LEVEL}-linux',
@@ -2297,8 +2328,7 @@ def MakeLinuxEnv():
   elif linux_env.Bit('build_arm'):
     SetupLinuxEnvArm(linux_env)
   elif linux_env.Bit('build_mips32'):
-    # TODO(petarj): Add support for MIPS.
-    pass
+    SetupLinuxEnvMips(linux_env)
   else:
     Banner('Strange platform: %s' % GetPlatform())
 
@@ -2315,7 +2345,7 @@ def MakeLinuxEnv():
       )
   # The ARM toolchain has a linker that doesn't handle the code its
   # compiler generates under -fPIE.
-  if linux_env.Bit('build_arm'):
+  if linux_env.Bit('build_arm') or linux_env.Bit('build_mips32'):
     linux_env.Prepend(CCFLAGS=['-fPIC'])
     # TODO(mcgrathr): Temporarily punt _FORTIFY_SOURCE for ARM because
     # it causes a libc dependency newer than the old bots have installed.