From fffa4c5aa5b5995ce88680170fb2288b10b05fbe Mon Sep 17 00:00:00 2001
From: Stephanos Ioannidis <root@stephanos.io>
Date: Mon, 7 Jun 2021 14:42:06 +0900
Subject: gcc: Allow setting custom target CXXFLAGS

This commit adds two additional arguments (`cxxflags_for_target` and
`extra_cxxflags_for_target`) for the gcc backend build function that
can be used to specify custom target CXXFLAGS.

By default, the target CXXFLAGS is set to the target CFLAGS. When
`cxxflags_for_target` is specified however, it overrides that behaviour
and allows setting different target CXXFLAGS from the target CFLAGS.

The `extra_cxxflags_for_target` argument can be used to specify the
extra target CXXFLAGS to be appended to the target CXXFLAGS. This is
useful when it is necessary to append CXX-specific flags to the
existing CFLAGS to be used as the target CXXFLAGS.

A useful application of this is building full and nano versions of
libstdc++ with different target CXXFLAGS as necessitated by
`nano.specs`.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

diff --git a/scripts/build/cc/gcc.sh b/scripts/build/cc/gcc.sh
index 39c70bb..dc391e4 100644
--- a/scripts/build/cc/gcc.sh
+++ b/scripts/build/cc/gcc.sh
@@ -295,7 +295,8 @@ do_gcc_core_backend() {
     local enable_optspace
     local complibs
     local lang_list
-    local cflags cflags_for_build cflags_for_target
+    local cflags cflags_for_build cflags_for_target cxxflags_for_target
+    local extra_cxxflags_for_target
     local ldflags
     local build_step
     local log_txt
@@ -611,6 +612,16 @@ do_gcc_core_backend() {
     # Assume '-O2' by default for building target libraries.
     cflags_for_target="-g -O2 ${cflags_for_target}"
 
+    # Set target CXXFLAGS to CFLAGS if none is provided.
+    if [ -z "${cxxflags_for_target}" ]; then
+        cxxflags_for_target="${cflags_for_target}"
+    fi
+
+    # Append extra CXXFLAGS if provided.
+    if [ -n "${extra_cxxflags_for_target}" ]; then
+        cxxflags_for_target="${cxxflags_for_target} ${extra_cxxflags_for_target}"
+    fi
+
     # Use --with-local-prefix so older gccs don't look in /usr/local (http://gcc.gnu.org/PR10532).
     # Pass only user-specified CFLAGS/LDFLAGS in CFLAGS_FOR_TARGET/LDFLAGS_FOR_TARGET: during
     # the build of, for example, libatomic, GCC tried to compile multiple variants for runtime
@@ -624,7 +635,7 @@ do_gcc_core_backend() {
     CXXFLAGS_FOR_BUILD="${cflags_for_build}"           \
     LDFLAGS="${core_LDFLAGS[*]}"                       \
     CFLAGS_FOR_TARGET="${cflags_for_target}"           \
-    CXXFLAGS_FOR_TARGET="${cflags_for_target}"         \
+    CXXFLAGS_FOR_TARGET="${cxxflags_for_target}"       \
     LDFLAGS_FOR_TARGET="${CT_TARGET_LDFLAGS}"          \
     ${CONFIG_SHELL}                                    \
     "${CT_SRC_DIR}/gcc/configure"                      \
@@ -940,6 +951,8 @@ do_gcc_backend() {
     local cflags
     local cflags_for_build
     local cflags_for_target
+    local cxxflags_for_target
+    local extra_cxxflags_for_target
     local ldflags
     local build_manuals
     local exec_prefix
@@ -1225,6 +1238,16 @@ do_gcc_backend() {
     # Assume '-O2' by default for building target libraries.
     cflags_for_target="-g -O2 ${cflags_for_target}"
 
+    # Set target CXXFLAGS to CFLAGS if none is provided.
+    if [ -z "${cxxflags_for_target}" ]; then
+        cxxflags_for_target="${cflags_for_target}"
+    fi
+
+    # Append extra CXXFLAGS if provided.
+    if [ -n "${extra_cxxflags_for_target}" ]; then
+        cxxflags_for_target="${cxxflags_for_target} ${extra_cxxflags_for_target}"
+    fi
+
     # NB: not using CT_ALL_TARGET_CFLAGS/CT_ALL_TARGET_LDFLAGS here!
     # See do_gcc_core_backend for explanation.
     CT_DoExecLog CFG                                   \
@@ -1235,7 +1258,7 @@ do_gcc_backend() {
     CXXFLAGS_FOR_BUILD="${cflags_for_build}"           \
     LDFLAGS="${final_LDFLAGS[*]}"                      \
     CFLAGS_FOR_TARGET="${cflags_for_target}"           \
-    CXXFLAGS_FOR_TARGET="${cflags_for_target}"         \
+    CXXFLAGS_FOR_TARGET="${cxxflags_for_target}"       \
     LDFLAGS_FOR_TARGET="${CT_TARGET_LDFLAGS}"          \
     ${CONFIG_SHELL}                                    \
     "${CT_SRC_DIR}/gcc/configure"                      \
-- 
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