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tools: Fix unavoidable GCC call in Clang builds

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In ChromeOS and Gentoo we catch any unwanted mixed Clang/LLVM
and GCC/binutils usage via toolchain wrappers which fail builds.
This has revealed that GCC is called unconditionally in Clang
configured builds to populate GCC_TOOLCHAIN_DIR.

Allow the user to override CLANG_CROSS_FLAGS to avoid the GCC
call - in our case we set the var directly in the ebuild recipe.

In theory Clang could be able to autodetect these settings so
this logic could be removed entirely, but in practice as the
commit cebdb73745 ("tools: Help cross-building with clang")
mentions, this does not always work, so giving distributions
more control to specify their flags & sysroot is beneficial.

Suggested-by: Manoj Gupta <manojgupta@chromium.com>
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/lkml/87czjk4osi.fsf@ryzen9.i-did-not-set--mail-host-address--so-tickle-me
Link: https://lore.kernel.org/bpf/20220308121428.81735-1-adrian.ratiu@collabora.com
This commit is contained in:
Adrian Ratiu 2022-03-08 14:14:28 +02:00 committed by Daniel Borkmann
parent d23a872032
commit 7fd9fd46a4
1 changed files with 4 additions and 0 deletions
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4
tools/scripts/Makefile.include
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@ -89,6 +89,9 @@ ifeq ($(CC_NO_CLANG), 1)
EXTRA_WARNINGS += -Wstrict-aliasing=3
else ifneq ($(CROSS_COMPILE),)
# Allow userspace to override CLANG_CROSS_FLAGS to specify their own
# sysroots and flags or to avoid the GCC call in pure Clang builds.
ifeq ($(CLANG_CROSS_FLAGS),)
CLANG_CROSS_FLAGS := --target=$(notdir $(CROSS_COMPILE:%-=%))
GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)gcc 2>/dev/null))
ifneq ($(GCC_TOOLCHAIN_DIR),)
@ -96,6 +99,7 @@ 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
endif # CLANG_CROSS_FLAGS
CFLAGS += $(CLANG_CROSS_FLAGS)
AFLAGS += $(CLANG_CROSS_FLAGS)
endif # CROSS_COMPILE