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Date: Sat, 30 Oct 2021 16:33:11 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Nathan Chancellor <nathan@...nel.org>,
Masahiro Yamada <masahiroy@...nel.org>,
Michal Marek <michal.lkml@...kovi.net>,
X86 ML <x86@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
llvm@...ts.linux.dev
Subject: Re: [PATCH] kbuild: Support clang-$ver builds
Latestest greatness... :-)
---
Subject: kbuild: Fix clang/llvm build infra
Debian (and derived) distros ship their compilers as -$ver suffixed
binaries. For gcc it is sufficent to use:
$ make CC=gcc-12
However, clang builds (esp. clang-lto) need a whole array of tools to be
exactly right, leading to unweildy stuff like:
$ make CC=clang-13 LD=ld.lld=14 AR=llvm-ar-13 NM=llvm-nm-13 OBJCOPY=llvm-objcopy-13 OBJDUMP=llvm-objdump-13 READELF=llvm-readelf-13 STRIP=llvm-strip-13 LLVM=1
which is, quite franktly, totally insane and unusable. Instead make
the CC variable DTRT, enabling one such as myself to use:
$ make CC=clang-13
This also lets one quickly test different clang versions.
Additionally, also support path based LLVM suites like:
$ make CC=/opt/llvm/bin/clang
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
Makefile | 45 +++++++++++++++++++++++++++---------
tools/scripts/Makefile.include | 50 ++++++++++++++++++++++++++++-------------
2 files changed, 68 insertions(+), 27 deletions(-)
--- a/Makefile
+++ b/Makefile
@@ -423,9 +423,29 @@ HOST_LFS_CFLAGS := $(shell getconf LFS_C
HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS 2>/dev/null)
HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null)
-ifneq ($(LLVM),)
-HOSTCC = clang
-HOSTCXX = clang++
+# powerpc and s390 don't yet work with LLVM as a whole
+ifeq ($(ARCH),powerpc)
+LLVM = 0
+endif
+ifeq ($(ARCH),s390)
+LLVM = 0
+endif
+
+# otherwise, if CC=clang, default to using LLVM to enable LTO
+CC_BASE := $(shell echo $(CC) | sed 's/.*\///')
+CC_NAME := $(shell echo $(CC_BASE) | cut -b "1-5")
+ifeq ($(shell test "$(CC_NAME)" = "clang"; echo $$?),0)
+LLVM ?= 1
+LLVM_PFX := $(shell echo $(CC) | sed 's/\(.*\/\)\?.*/\1/')
+LLVM_SFX := $(shell echo $(CC_BASE) | cut -b "6-")
+endif
+
+# if not set by now, do not use LLVM
+LLVM ?= 0
+
+ifneq ($(LLVM),0)
+HOSTCC = $(LLVM_PFX)clang$(LLVM_SFX)
+HOSTCXX = $(LLVM_PFX)clang++$(LLVM_SFX)
else
HOSTCC = gcc
HOSTCXX = g++
@@ -442,15 +462,15 @@ KBUILD_HOSTLDLIBS := $(HOST_LFS_LIBS)
# Make variables (CC, etc...)
CPP = $(CC) -E
-ifneq ($(LLVM),)
-CC = clang
-LD = ld.lld
-AR = llvm-ar
-NM = llvm-nm
-OBJCOPY = llvm-objcopy
-OBJDUMP = llvm-objdump
-READELF = llvm-readelf
-STRIP = llvm-strip
+ifneq ($(LLVM),0)
+CC = $(LLVM_PFX)clang$(LLVM_SFX)
+LD = $(LLVM_PFX)ld.lld$(LLVM_SFX)
+AR = $(LLVM_PFX)llvm-ar$(LLVM_SFX)
+NM = $(LLVM_PFX)llvm-nm$(LLVM_SFX)
+OBJCOPY = $(LLVM_PFX)llvm-objcopy$(LLVM_SFX)
+OBJDUMP = $(LLVM_PFX)llvm-objdump$(LLVM_SFX)
+READELF = $(LLVM_PFX)llvm-readelf$(LLVM_SFX)
+STRIP = $(LLVM_PFX)llvm-strip$(LLVM_SFX)
else
CC = $(CROSS_COMPILE)gcc
LD = $(CROSS_COMPILE)ld
@@ -461,6 +481,7 @@ OBJDUMP = $(CROSS_COMPILE)objdump
READELF = $(CROSS_COMPILE)readelf
STRIP = $(CROSS_COMPILE)strip
endif
+
PAHOLE = pahole
RESOLVE_BTFIDS = $(objtree)/tools/bpf/resolve_btfids/resolve_btfids
LEX = flex
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -51,12 +51,32 @@ define allow-override
$(eval $(1) = $(2)))
endef
-ifneq ($(LLVM),)
-$(call allow-override,CC,clang)
-$(call allow-override,AR,llvm-ar)
-$(call allow-override,LD,ld.lld)
-$(call allow-override,CXX,clang++)
-$(call allow-override,STRIP,llvm-strip)
+# powerpc and s390 don't yet work with LLVM as a whole
+ifeq ($(ARCH),powerpc)
+LLVM = 0
+endif
+ifeq ($(ARCH),s390)
+LLVM = 0
+endif
+
+# otherwise, if CC=clang, default to using LLVM to enable LTO
+CC_BASE := $(shell echo $(CC) | sed 's/.*\///')
+CC_NAME := $(shell echo $(CC_BASE) | cut -b "1-5")
+ifeq ($(shell test "$(CC_NAME)" = "clang"; echo $$?),0)
+LLVM ?= 1
+LLVM_PFX := $(shell echo $(CC) | sed 's/\(.*\/\)\?.*/\1/')
+LLVM_SFX := $(shell echo $(CC_BASE) | cut -b "6-")
+endif
+
+# if not set by now, do not use LLVM
+LLVM ?= 0
+
+ifneq ($(LLVM),0)
+$(call allow-override,CC,$(LLVM_PFX)clang$(LLVM_SFX))
+$(call allow-override,AR,$(LLVM_PFX)llvm-ar$(LLVM_SFX))
+$(call allow-override,LD,$(LLVM_PFX)ld.lld$(LLVM_SFX))
+$(call allow-override,CXX,$(LLVM_PFX)clang++$(LLVM_SFX))
+$(call allow-override,STRIP,$(LLVM_PFX)llvm-strip$(LLVM_SFX))
else
# Allow setting various cross-compile vars or setting CROSS_COMPILE as a prefix.
$(call allow-override,CC,$(CROSS_COMPILE)gcc)
@@ -68,10 +88,10 @@ endif
CC_NO_CLANG := $(shell $(CC) -dM -E -x c /dev/null | grep -Fq "__clang__"; echo $$?)
-ifneq ($(LLVM),)
-HOSTAR ?= llvm-ar
-HOSTCC ?= clang
-HOSTLD ?= ld.lld
+ifneq ($(LLVM),0)
+HOSTAR ?= $(LLVM_PFX)llvm-ar$(LLVM_SFX)
+HOSTCC ?= $(LLVM_PFX)clang$(LLVM_SFX)
+HOSTLD ?= $(LLVM_PFX)ld.lld$(LLVM_SFX)
else
HOSTAR ?= ar
HOSTCC ?= gcc
@@ -79,11 +99,11 @@ HOSTLD ?= ld
endif
# Some tools require Clang, LLC and/or LLVM utils
-CLANG ?= clang
-LLC ?= llc
-LLVM_CONFIG ?= llvm-config
-LLVM_OBJCOPY ?= llvm-objcopy
-LLVM_STRIP ?= llvm-strip
+CLANG ?= $(LLVM_PFX)clang$(LLVM_SFX)
+LLC ?= $(LLVM_PFX)llc$(LLVM_SFX)
+LLVM_CONFIG ?= $(LLVM_PFX)llvm-config$(LLVM_SFX)
+LLVM_OBJCOPY ?= $(LLVM_PFX)llvm-objcopy$(LLVM_SFX)
+LLVM_STRIP ?= $(LLVM_PFX)llvm-strip$(LLVM_SFX)
ifeq ($(CC_NO_CLANG), 1)
EXTRA_WARNINGS += -Wstrict-aliasing=3
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