linux-kernel - [PATCH v2 1/2] Makefile: Remove '--gcc-toolchain' flag

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Date:   Tue,  9 Mar 2021 13:59:14 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Sedat Dilek <sedat.dilek@...il.com>,
        Fangrui Song <maskray@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH v2 1/2] Makefile: Remove '--gcc-toolchain' flag

This flag was originally added to allow clang to find the GNU cross
tools in commit 785f11aa595b ("kbuild: Add better clang cross build
support"). This flag was not enough to find the tools at times so
'--prefix' was added to the list in commit ef8c4ed9db80 ("kbuild: allow
to use GCC toolchain not in Clang search path") and improved upon in
commit ca9b31f6bb9c ("Makefile: Fix GCC_TOOLCHAIN_DIR prefix for Clang
cross compilation"). Now that '--prefix' specifies a full path and
prefix, '--gcc-toolchain' serves no purpose because the kernel builds
with '-nostdinc' and '-nostdlib'.

This has been verified with self compiled LLVM 10.0.1 and LLVM 13.0.0 as
well as a distribution version of LLVM 11.1.0 without binutils in the
LLVM toolchain locations.

Link: https://reviews.llvm.org/D97902
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---

v1 -> v2:

* Improve commit message (add history behind flag and link to Fangrui's
  documentation improvement).

I did not carry tags forward so that people could re-review and test.

 Makefile | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/Makefile b/Makefile
index 31dcdb3d61fa..182e93d91198 100644
--- a/Makefile
+++ b/Makefile
@@ -568,10 +568,6 @@ ifneq ($(CROSS_COMPILE),)
 CLANG_FLAGS	+= --target=$(notdir $(CROSS_COMPILE:%-=%))
 GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
 CLANG_FLAGS	+= --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
-GCC_TOOLCHAIN	:= $(realpath $(GCC_TOOLCHAIN_DIR)/..)
-endif
-ifneq ($(GCC_TOOLCHAIN),)
-CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
 endif
 ifneq ($(LLVM_IAS),1)
 CLANG_FLAGS	+= -no-integrated-as

base-commit: a38fd8748464831584a19438cbb3082b5a2dab15
-- 
2.31.0.rc1