scons: allow passing arbitrary CCFLAGS and LDFLAGS from the CLI

The flags may be passed as:

scons CCFLAGS_EXTRA='-Wno-error -pedantic' \
      LDFLAGS_EXTRA='-g -g' build/<arch>/gem5.opt

The initial motivation for this commit is to help disable warning that
have become errors while bisecting.

scons orders the flags by Append call order, and ideally these flags
should be added last to override the others, since the last GCC flags
take precedence. However I haven't found a simple way to put them at
the very end.

Change-Id: Ida24dfb9604d88b99f113392ab5e47d578ba7259
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19048
Reviewed-by: Juha Jäykkä <juha.jaykka@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>

diff --git a/SConstruct b/SConstruct
index 28999a5b584af1dd7ac1fcc8213e0719e4ef6330..9e27b484c4308a2bfc7a4b85e6e7867a278d5df1 100755 (executable)
--- a/SConstruct
+++ b/SConstruct
@@ -1,6 +1,6 @@
 # -*- mode:python -*-
 
-# Copyright (c) 2013, 2015-2017 ARM Limited
+# Copyright (c) 2013, 2015-2017, 2019 ARM Limited
 # All rights reserved.
 #
 # The license below extends only to copyright in the software and shall
@@ -290,6 +290,8 @@ global_vars = Variables(global_vars_file, args=ARGUMENTS)
 global_vars.AddVariables(
     ('CC', 'C compiler', environ.get('CC', main['CC'])),
     ('CXX', 'C++ compiler', environ.get('CXX', main['CXX'])),
+    ('CCFLAGS_EXTRA', 'Extra C and C++ compiler flags', ''),
+    ('LDFLAGS_EXTRA', 'Extra linker flags', ''),
     ('PYTHON_CONFIG', 'Python config binary to use',
      [ 'python2.7-config', 'python-config' ]),
     ('PROTOC', 'protoc tool', environ.get('PROTOC', 'protoc')),
@@ -1285,6 +1287,9 @@ for variant_path in variant_paths:
     if env['USE_SSE2']:
         env.Append(CCFLAGS=['-msse2'])
 
+    env.Append(CCFLAGS='$CCFLAGS_EXTRA')
+    env.Append(LINKFLAGS='$LDFLAGS_EXTRA')
+
     # The src/SConscript file sets up the build rules in 'env' according
     # to the configured variables.  It returns a list of environments,
     # one for each variant build (debug, opt, etc.)