[Buildroot] [PATCH v11 8/9] package/clang: install a toolchain-wrapper for the host clang cross-compiler

Matt Weber matthew.weber at rockwellcollins.com
Thu Mar 11 14:29:31 UTC 2021

From: Romain Naour <romain.naour at smile.fr>

In order to use Clang as a host cross-compiler for Buildroot, we
need to provide at least the path to the sysroot (using
--sysroot) and some other compiler flags.

This series looks to reuse the toolchain wrapper for GCC since
Clang support most of the gcc flags used in the Buildroot's
toolchain wrapper. The only flag -mfused-madd (deprecated
since gcc 4.6) for mips is not supported by clang. Since
Clang require gcc >= 5.x this flag can never be used.

host-clang refers to an existing GCC-based toolchain (internal or
external) for libstdc++. However, a Buildroot external toolchain
gets a different BR_CROSS_PATH_SUFFIX. Therefore, we can't reuse the
toolchain-wrapper that gets built for the GCC-based toolchain, but
instead have to compile an additional clang-specific wrapper, called

After building the clang toolchain wrapper, create the symlinks needed
to force package infrastructure to use clang througt the wrapper.

Initially clang install the clang-8 binary and create all other symlinks:

 # clang -> clang-8
 # clang++ -> clang
 # clang-8
 # clang-cl -> clang
 # clang-cpp -> clang

Use a post install hook to rename the clang-8 binary to clang-8.br_real
and recreate all symlinks:

 # clang -> toolchain-wrapper-clang
 # clang++ -> toolchain-wrapper-clang
 # clang-8 -> toolchain-wrapper-clang
 # clang-8.br_real
 # clang++.br_real -> clang-8.br_real
 # clang.br_real -> clang-8.br_real
 # clang-cl -> toolchain-wrapper-clang
 # clang-cl.br_real -> clang-8.br_real
 # clang-cpp -> toolchain-wrapper-clang
 # clang-cpp.br_real -> clang-8.br_real

NOTE: *.br_real symlinks are needed as the wrapper references them

Use the previously introduced CLANG_VERSION_MAJOR variable to create
theses symlinks.

Set BR_CROSS_PATH_SUFFIX to ".br_real" as for the Buildroot's internal
GCC toolchain backend to find the "real" clang binary installed in

build and install the specific clang toolchain wrapper.

Signed-off-by: Romain Naour <romain.naour at smile.fr>
Cc: Valentin Korenblit <valentinkorenblit at gmail.com>
Signed-off-by: Matthew Weber <matthew.weber at rockwellcollins.com>

v1 -> v2
 - Fixup commit description and clarified *.br_real
 - Simplified loop
 package/clang/clang.mk | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/package/clang/clang.mk b/package/clang/clang.mk
index 95b4964be3..3c75f8d6b1 100644
--- a/package/clang/clang.mk
+++ b/package/clang/clang.mk
@@ -112,5 +112,33 @@ ifeq ($(BR2_TOOLCHAIN_EXTERNAL),y)
+	$(Q)cd $(HOST_DIR)/bin; \
+	rm -f clang-$(CLANG_VERSION_MAJOR).br_real; \
+	mv clang-$(CLANG_VERSION_MAJOR) clang-$(CLANG_VERSION_MAJOR).br_real; \
+	ln -sf toolchain-wrapper-clang clang-$(CLANG_VERSION_MAJOR); \
+	for i in clang clang++ clang-cl clang-cpp; do \
+		ln -snf toolchain-wrapper-clang $$i; \
+		ln -snf clang-$(CLANG_VERSION_MAJOR).br_real $$i.br_real; \
+	done
+		-s -Wl,--hash-style=$(TOOLCHAIN_WRAPPER_HASH_STYLE) \
+		toolchain/toolchain-wrapper.c \
+		-o $(@D)/toolchain-wrapper-clang
+	$(INSTALL) -D -m 0755 $(@D)/toolchain-wrapper-clang \
+		$(HOST_DIR)/bin/toolchain-wrapper-clang
 $(eval $(cmake-package))
 $(eval $(host-cmake-package))

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