linux-kernel - [PATCH] scripts/Makefile.clang: set --target for host based on make -v

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Message-Id: <20220617203948.3714905-1-ndesaulniers@google.com>
Date:   Fri, 17 Jun 2022 13:39:48 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH] scripts/Makefile.clang: set --target for host based on make -v

We're working on providing statically linked images of clang to host on
kernel.org. We're building them in Alpine Linux based Docker containers,
which are MUSL based systems.

In order to keep bootstrapping simpler, I'd like for them to have an
implicit default --target of x86_64-alpine-linux-musl (set via LLVM's
cmake variable LLVM_DEFAULT_TARGET_TRIPLE).

Similarly, if one were to use a different build of clang meant for a
glibc or bionic based system on a MUSL based host, we'd prefer to use
the correct MUSL based triple for target hosts.

Borrowed from the Zen of Python: Explicit is better than implicit. Let's
be explicit about the target triple for HOSTCC when building with
HOSTCC=clang or LLVM=1.

Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 Makefile               |  3 +--
 scripts/Makefile.clang | 10 ++++++++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 1a6678d817bd..87712d9b043c 100644
--- a/Makefile
+++ b/Makefile
@@ -600,10 +600,9 @@ endif
 # CC_VERSION_TEXT is referenced from Kconfig (so it needs export),
 # and from include/config/auto.conf.cmd to detect the compiler upgrade.
 CC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(CC) --version 2>/dev/null | head -n 1))
+HOSTCC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(HOSTCC) --version 2>/dev/null | head -n 1))
 
-ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
 include $(srctree)/scripts/Makefile.clang
-endif
 
 # Include this also for config targets because some architectures need
 # cc-cross-prefix to determine CROSS_COMPILE.
diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
index 87285b76adb2..a4505cd62d7b 100644
--- a/scripts/Makefile.clang
+++ b/scripts/Makefile.clang
@@ -1,3 +1,4 @@
+ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
 # Individual arch/{arch}/Makefiles should use -EL/-EB to set intended
 # endianness and -m32/-m64 to set word size based on Kconfigs instead of
 # relying on the target triple.
@@ -39,3 +40,12 @@ CLANG_FLAGS	+= -Werror=ignored-optimization-argument
 KBUILD_CFLAGS	+= $(CLANG_FLAGS)
 KBUILD_AFLAGS	+= $(CLANG_FLAGS)
 export CLANG_FLAGS
+endif
+
+# If HOSTCC is clang, set the host target triple explicitly; do not rely on
+# implicit defaults.
+ifneq ($(findstring clang,$(HOSTCC_VERSION_TEXT)),)
+HOST_TRIPLE		:= --target=$(shell make --version | head -n2 | tail -n1 | cut -d ' ' -f 3)
+KBUILD_HOSTCFLAGS	+= $(HOST_TRIPLE)
+KBUILD_HOSTLDFLAGS	+= $(HOST_TRIPLE)
+endif

base-commit: 79fe0f863f920c5fcf9dea61676742f813f0b7a6
-- 
2.36.1.476.g0c4daa206d-goog