xcompile: Fix clang compiler runtime detection

clang, like gcc, needs a compiler runtime library. Unlike gcc, it can
use either its own runtime library (compiler-rt), or gcc's version
(libgcc). Also unlike gcc, the version of clang that is currently part
of our reference toolchain does not provide the necessary versions of
compiler-rt for all platforms we support. Hence, for now, use libgcc
even on clang builds.  This patch allows switching between the two, but
switching to compiler-rt will break clang builds, unless someone fixes
our reference toolchain to provide libclang_rt.builtins-${ARCH}.a for
each of our supported platforms.

Change-Id: I5001a4b62ed34df19312f980b927ced8cbaf07db
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: https://review.coreboot.org/20303
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/util/xcompile/xcompile b/util/xcompile/xcompile
index 347ae8e2a5..63f1ca9cf5 100755
--- a/util/xcompile/xcompile
+++ b/util/xcompile/xcompile
@@ -206,10 +206,14 @@ detect_special_flags() {
 }
 
 detect_compiler_runtime() {
-	test -z "$CLANG" || \
-	CC_RT_CLANG="$(${CLANG} -print-libgcc-file-name 2>/dev/null)"
 	test -z "$GCC" || \
 	CC_RT_GCC="$(${GCC} ${CFLAGS_GCC} -print-libgcc-file-name)"
+	if [ ${CLANG_RUNTIME} = "libgcc" ]; then
+		CC_RT_CLANG=${CC_RT_GCC}
+	else
+		test -z "$CLANG" || \
+		  CC_RT_CLANG="$(${CLANG} ${CFLAGS_CLANG} -print-libgcc-file-name 2>/dev/null)"
+	fi
 }
 
 report_arch_toolchain() {
@@ -371,6 +375,14 @@ arch_config_power8() {
 	CC_RT_EXTRA_GCC="-mcpu=power8 -mbig-endian"
 }
 
+# Right now, the clang reference toolchain is not building compiler-rt builtins
+# for any of the cross compile architectures. Hence we use libgcc for now,
+# because that is available and lets us proceed with getting coreboot clang
+# ready. Toggle CLANG_RUNTIME if you want to experiment with compiler-rt.
+
+CLANG_RUNTIME="libgcc"
+# CLANG_RUNTIME="compiler-rt"
+
 test_architecture() {
 	local architecture=$1
 	local endian gccprefix search
@@ -431,7 +443,7 @@ test_architecture() {
 		# but that's more of a clang limitation. Let's be optimistic
 		# that this will change in the future.
 		CLANG="${XGCCPATH}clang"
-		CFLAGS_CLANG="-target ${clang_arch}-${TABI} $CFLAGS_CLANG -ccc-gcc-name ${GCC}"
+		CFLAGS_CLANG="-target ${clang_arch}-${TABI} --rtlib=${CLANG_RUNTIME} $CFLAGS_CLANG -ccc-gcc-name ${GCC}"
 	fi
 }