From: Jean-Philippe Brucker <jean-philippe@linaro.org>
Date: Thu, 16 Dec 2021 16:38:38 +0000
Subject: tools: Help cross-building with clang
Patch-mainline: v5.17-rc1
Git-commit: cebdb7374577ac6e14afb11311af8c2c44a259fa
References: jsc#PED-1368
Cross-compilation with clang uses the -target parameter rather than a
toolchain prefix. Just like the kernel Makefile, add that parameter to
CFLAGS when CROSS_COMPILE is set.
Unlike the kernel Makefile, we use the --sysroot and --gcc-toolchain
options because unlike the kernel, tools require standard libraries.
Commit c91d4e47e10e ("Makefile: Remove '--gcc-toolchain' flag") provides
some background about --gcc-toolchain. Normally clang finds on its own
the additional utilities and libraries that it needs (for example GNU ld
or glibc). On some systems however, this autodetection doesn't work.
There, our only recourse is asking GCC directly, and pass the result to
--sysroot and --gcc-toolchain. Of course that only works when a cross
GCC is available.
Autodetection worked fine on Debian, but to use the aarch64-linux-gnu
toolchain from Archlinux I needed both --sysroot (for crt1.o) and
--gcc-toolchain (for crtbegin.o, -lgcc). The --prefix parameter wasn't
needed there, but it might be useful on other distributions.
Use the CLANG_CROSS_FLAGS variable instead of CLANG_FLAGS because it
allows tools such as bpftool, that need to build both host and target
binaries, to easily filter out the cross-build flags from CFLAGS.
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/bpf/20211216163842.829836-2-jean-philippe@linaro.org
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
tools/scripts/Makefile.include | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -87,7 +87,18 @@ LLVM_STRIP ?= llvm-strip
ifeq ($(CC_NO_CLANG), 1)
EXTRA_WARNINGS += -Wstrict-aliasing=3
-endif
+
+else ifneq ($(CROSS_COMPILE),)
+CLANG_CROSS_FLAGS := --target=$(notdir $(CROSS_COMPILE:%-=%))
+GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)gcc))
+ifneq ($(GCC_TOOLCHAIN_DIR),)
+CLANG_CROSS_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
+CLANG_CROSS_FLAGS += --sysroot=$(shell $(CROSS_COMPILE)gcc -print-sysroot)
+CLANG_CROSS_FLAGS += --gcc-toolchain=$(realpath $(GCC_TOOLCHAIN_DIR)/..)
+endif # GCC_TOOLCHAIN_DIR
+CFLAGS += $(CLANG_CROSS_FLAGS)
+AFLAGS += $(CLANG_CROSS_FLAGS)
+endif # CROSS_COMPILE
# Hack to avoid type-punned warnings on old systems such as RHEL5:
# We should be changing CFLAGS and checking gcc version, but this