LLVM=1 patches for 5.4

LLVM=1 patches for 5.4

[Nick Desaulniers]

[-- Attachment #1: Type: text/plain, Size: 1982 bytes --]

Dear stable kernel maintainers,
Please consider the attached mbox file, which contains 9 patches which
cherry pick cleanly onto 5.4:

1. commit fcf1b6a35c16 ("Documentation/llvm: add documentation on
building w/ Clang/LLVM")
2. commit 0f44fbc162b7 ("Documentation/llvm: fix the name of llvm-size")
3. commit 63b903dfebde ("net: wan: wanxl: use allow to pass
CROSS_COMPILE_M68k for rebuilding firmware")
4. commit 734f3719d343 ("net: wan: wanxl: use $(M68KCC) instead of
$(M68KAS) for rebuilding firmware")
5. commit eefb8c124fd9 ("x86/boot: kbuild: allow readelf executable to
be specified")
6. commit 94f7345b7124 ("kbuild: remove PYTHON2 variable")
7. commit aa824e0c962b ("kbuild: remove AS variable")
8. commit 7e20e47c70f8 ("kbuild: replace AS=clang with LLVM_IAS=1")
9. commit a0d1c951ef08 ("kbuild: support LLVM=1 to switch the default
tools to Clang/LLVM")

This series improves/simplifies building kernels with Clang and LLVM
utilities; it will help the various CI systems testing kernels built
with Clang+LLVM utilities (in fact I will be pointing to this, if
accepted, next week at plumbers with those CI system maintainers), and
we will make immediate use of it in Android (see also:
https://android-review.googlesource.com/c/platform/prebuilts/clang/host/linux-x86/+/1405387).
We can always carry it out of tree in Android, but I think the series
is fairly tame, and would prefer not to.

I only particularly care about 5+8+9 (eefb8c124fd9, 7e20e47c70f8, and
a0d1c951ef08), but the rest are required for them to cherry-pick
cleanly.  I don't mind separating those three out, though they won't
be clean cherry-picks at that point.  It might be good to have
Masahiro review the series.  If accepted, I plan to wire up test
coverage of these immediately in
https://github.com/ClangBuiltLinux/continuous-integration/issues/300.

Most of the above landed in v5.7-rc1, with 94f7345b7124 landing in
v5.6-rc1 and eefb8c124fd9 landing in v5.5-rc3.
-- 
Thanks,
~Nick Desaulniers

[-- Attachment #2: llvm_1.mbox --]
[-- Type: application/octet-stream, Size: 24912 bytes --]

From 52dd5c2a6ce76063f3db72796940de5660be3ca4 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers@google.com>
Date: Wed, 26 Feb 2020 15:23:36 -0800
Subject: [PATCH 1/9] Documentation/llvm: add documentation on building w/
 Clang/LLVM

commit fcf1b6a35c16ac500fa908a4022238e5d666eabf upstream.

added to kbuild documentation. Provides more official info on building
kernels with Clang and LLVM than our wiki.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---
 Documentation/kbuild/index.rst |  1 +
 Documentation/kbuild/llvm.rst  | 80 ++++++++++++++++++++++++++++++++++
 MAINTAINERS                    |  1 +
 3 files changed, 82 insertions(+)
 create mode 100644 Documentation/kbuild/llvm.rst

diff --git a/Documentation/kbuild/index.rst b/Documentation/kbuild/index.rst
index 0f144fad99a6..3882bd5f7728 100644
--- a/Documentation/kbuild/index.rst
+++ b/Documentation/kbuild/index.rst
@@ -19,6 +19,7 @@ Kernel Build System
 
     issues
     reproducible-builds
+    llvm
 
 .. only::  subproject and html
 
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
new file mode 100644
index 000000000000..d6c79eb4e23e
--- /dev/null
+++ b/Documentation/kbuild/llvm.rst
@@ -0,0 +1,80 @@
+==============================
+Building Linux with Clang/LLVM
+==============================
+
+This document covers how to build the Linux kernel with Clang and LLVM
+utilities.
+
+About
+-----
+
+The Linux kernel has always traditionally been compiled with GNU toolchains
+such as GCC and binutils. Ongoing work has allowed for `Clang
+<https://clang.llvm.org/>`_ and `LLVM <https://llvm.org/>`_ utilities to be
+used as viable substitutes. Distributions such as `Android
+<https://www.android.com/>`_, `ChromeOS
+<https://www.chromium.org/chromium-os>`_, and `OpenMandriva
+<https://www.openmandriva.org/>`_ use Clang built kernels.  `LLVM is a
+collection of toolchain components implemented in terms of C++ objects
+<https://www.aosabook.org/en/llvm.html>`_. Clang is a front-end to LLVM that
+supports C and the GNU C extensions required by the kernel, and is pronounced
+"klang," not "see-lang."
+
+Clang
+-----
+
+The compiler used can be swapped out via `CC=` command line argument to `make`.
+`CC=` should be set when selecting a config and during a build.
+
+	make CC=clang defconfig
+
+	make CC=clang
+
+Cross Compiling
+---------------
+
+A single Clang compiler binary will typically contain all supported backends,
+which can help simplify cross compiling.
+
+	ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang
+
+`CROSS_COMPILE` is not used to prefix the Clang compiler binary, instead
+`CROSS_COMPILE` is used to set a command line flag: `--target <triple>`. For
+example:
+
+	clang --target aarch64-linux-gnu foo.c
+
+LLVM Utilities
+--------------
+
+LLVM has substitutes for GNU binutils utilities. These can be invoked as
+additional parameters to `make`.
+
+	make CC=clang AS=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
+	  OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-objsize \\
+	  READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\
+	  HOSTLD=ld.lld
+
+Getting Help
+------------
+
+- `Website <https://clangbuiltlinux.github.io/>`_
+- `Mailing List <https://groups.google.com/forum/#!forum/clang-built-linux>`_: <clang-built-linux@googlegroups.com>
+- `Issue Tracker <https://github.com/ClangBuiltLinux/linux/issues>`_
+- IRC: #clangbuiltlinux on chat.freenode.net
+- `Telegram <https://t.me/ClangBuiltLinux>`_: @ClangBuiltLinux
+- `Wiki <https://github.com/ClangBuiltLinux/linux/wiki>`_
+- `Beginner Bugs <https://github.com/ClangBuiltLinux/linux/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22>`_
+
+Getting LLVM
+-------------
+
+- http://releases.llvm.org/download.html
+- https://github.com/llvm/llvm-project
+- https://llvm.org/docs/GettingStarted.html
+- https://llvm.org/docs/CMake.html
+- https://apt.llvm.org/
+- https://www.archlinux.org/packages/extra/x86_64/llvm/
+- https://github.com/ClangBuiltLinux/tc-build
+- https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source
+- https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/
diff --git a/MAINTAINERS b/MAINTAINERS
index fe6fa5d3a63e..1407008df749 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4028,6 +4028,7 @@ B:	https://github.com/ClangBuiltLinux/linux/issues
 C:	irc://chat.freenode.net/clangbuiltlinux
 S:	Supported
 K:	\b(?i:clang|llvm)\b
+F:	Documentation/kbuild/llvm.rst
 
 CLEANCACHE API
 M:	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
-- 
2.28.0.297.g1956fa8f8d-goog


From 32f506fb476d511da81dc550d64e430da237da49 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Thu, 2 Apr 2020 10:38:42 -0700
Subject: [PATCH 2/9] Documentation/llvm: fix the name of llvm-size

commit 0f44fbc162b737ff6251ae248184390ae2279fee upstream.

The tool is called llvm-size, not llvm-objsize.

Fixes: fcf1b6a35c16 ("Documentation/llvm: add documentation on building w/ Clang/LLVM")
Signed-off-by: Fangrui Song <maskray@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Documentation/kbuild/llvm.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
index d6c79eb4e23e..eefbdfa3e4d9 100644
--- a/Documentation/kbuild/llvm.rst
+++ b/Documentation/kbuild/llvm.rst
@@ -51,7 +51,7 @@ LLVM has substitutes for GNU binutils utilities. These can be invoked as
 additional parameters to `make`.
 
 	make CC=clang AS=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
-	  OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-objsize \\
+	  OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-size \\
 	  READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\
 	  HOSTLD=ld.lld
 
-- 
2.28.0.297.g1956fa8f8d-goog


From ca258a40a1675124f0b423833b1c9821d7f6055e Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Thu, 26 Mar 2020 14:57:15 +0900
Subject: [PATCH 3/9] net: wan: wanxl: use allow to pass CROSS_COMPILE_M68k for
 rebuilding firmware

commit 63b903dfebdea92aa92ad337d8451a6fbfeabf9d upstream.

As far as I understood from the Kconfig help text, this build rule is
used to rebuild the driver firmware, which runs on an old m68k-based
chip. So, you need m68k tools for the firmware rebuild.

wanxl.c is a PCI driver, but CONFIG_M68K does not select CONFIG_HAVE_PCI.
So, you cannot enable CONFIG_WANXL_BUILD_FIRMWARE for ARCH=m68k. In other
words, ifeq ($(ARCH),m68k) is false here.

I am keeping the dead code for now, but rebuilding the firmware requires
'as68k' and 'ld68k', which I do not have in hand.

Instead, the kernel.org m68k GCC [1] successfully built it.

Allowing a user to pass in CROSS_COMPILE_M68K= is handier.

[1] https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/9.2.0/x86_64-gcc-9.2.0-nolibc-m68k-linux.tar.xz

Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 drivers/net/wan/Kconfig  |  2 +-
 drivers/net/wan/Makefile | 12 ++++++------
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wan/Kconfig b/drivers/net/wan/Kconfig
index dd1a147f2971..058d77d2e693 100644
--- a/drivers/net/wan/Kconfig
+++ b/drivers/net/wan/Kconfig
@@ -200,7 +200,7 @@ config WANXL_BUILD_FIRMWARE
 	depends on WANXL && !PREVENT_FIRMWARE_BUILD
 	help
 	  Allows you to rebuild firmware run by the QUICC processor.
-	  It requires as68k, ld68k and hexdump programs.
+	  It requires m68k toolchains and hexdump programs.
 
 	  You should never need this option, say N.
 
diff --git a/drivers/net/wan/Makefile b/drivers/net/wan/Makefile
index 701f5d2fe3b6..995277c657a1 100644
--- a/drivers/net/wan/Makefile
+++ b/drivers/net/wan/Makefile
@@ -40,17 +40,17 @@ $(obj)/wanxl.o:	$(obj)/wanxlfw.inc
 
 ifeq ($(CONFIG_WANXL_BUILD_FIRMWARE),y)
 ifeq ($(ARCH),m68k)
-  AS68K = $(AS)
-  LD68K = $(LD)
+  M68KAS = $(AS)
+  M68KLD = $(LD)
 else
-  AS68K = as68k
-  LD68K = ld68k
+  M68KAS = $(CROSS_COMPILE_M68K)as
+  M68KLD = $(CROSS_COMPILE_M68K)ld
 endif
 
 quiet_cmd_build_wanxlfw = BLD FW  $@
       cmd_build_wanxlfw = \
-	$(CPP) -D__ASSEMBLY__ -Wp,-MD,$(depfile) -I$(srctree)/include/uapi $< | $(AS68K) -m68360 -o $(obj)/wanxlfw.o; \
-	$(LD68K) --oformat binary -Ttext 0x1000 $(obj)/wanxlfw.o -o $(obj)/wanxlfw.bin; \
+	$(CPP) -D__ASSEMBLY__ -Wp,-MD,$(depfile) -I$(srctree)/include/uapi $< | $(M68KAS) -m68360 -o $(obj)/wanxlfw.o; \
+	$(M68KLD) --oformat binary -Ttext 0x1000 $(obj)/wanxlfw.o -o $(obj)/wanxlfw.bin; \
 	hexdump -ve '"\n" 16/1 "0x%02X,"' $(obj)/wanxlfw.bin | sed 's/0x  ,//g;1s/^/static const u8 firmware[]={/;$$s/,$$/\n};\n/' >$(obj)/wanxlfw.inc; \
 	rm -f $(obj)/wanxlfw.bin $(obj)/wanxlfw.o
 
-- 
2.28.0.297.g1956fa8f8d-goog


From 791d921e52348413f842c7e33148617e696c02fe Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Thu, 26 Mar 2020 14:57:16 +0900
Subject: [PATCH 4/9] net: wan: wanxl: use $(M68KCC) instead of $(M68KAS) for
 rebuilding firmware

commit 734f3719d3438f9cc181d674c33ca9762e9148a1 upstream.

The firmware source, wanxlfw.S, is currently compiled by the combo of
$(CPP) and $(M68KAS). This is not what we usually do for compiling *.S
files. In fact, this Makefile is the only user of $(AS) in the kernel
build.

Instead of combining $(CPP) and (AS) from different tool sets, using
$(M68KCC) as an assembler driver is simpler, and saner.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 drivers/net/wan/Makefile | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wan/Makefile b/drivers/net/wan/Makefile
index 995277c657a1..cf7a0a65aae8 100644
--- a/drivers/net/wan/Makefile
+++ b/drivers/net/wan/Makefile
@@ -40,16 +40,16 @@ $(obj)/wanxl.o:	$(obj)/wanxlfw.inc
 
 ifeq ($(CONFIG_WANXL_BUILD_FIRMWARE),y)
 ifeq ($(ARCH),m68k)
-  M68KAS = $(AS)
+  M68KCC = $(CC)
   M68KLD = $(LD)
 else
-  M68KAS = $(CROSS_COMPILE_M68K)as
+  M68KCC = $(CROSS_COMPILE_M68K)gcc
   M68KLD = $(CROSS_COMPILE_M68K)ld
 endif
 
 quiet_cmd_build_wanxlfw = BLD FW  $@
       cmd_build_wanxlfw = \
-	$(CPP) -D__ASSEMBLY__ -Wp,-MD,$(depfile) -I$(srctree)/include/uapi $< | $(M68KAS) -m68360 -o $(obj)/wanxlfw.o; \
+	$(M68KCC) -D__ASSEMBLY__ -Wp,-MD,$(depfile) -I$(srctree)/include/uapi -c -o $(obj)/wanxlfw.o $<; \
 	$(M68KLD) --oformat binary -Ttext 0x1000 $(obj)/wanxlfw.o -o $(obj)/wanxlfw.bin; \
 	hexdump -ve '"\n" 16/1 "0x%02X,"' $(obj)/wanxlfw.bin | sed 's/0x  ,//g;1s/^/static const u8 firmware[]={/;$$s/,$$/\n};\n/' >$(obj)/wanxlfw.inc; \
 	rm -f $(obj)/wanxlfw.bin $(obj)/wanxlfw.o
-- 
2.28.0.297.g1956fa8f8d-goog


From 963cdc94b730d2a5ba8b5cebd65337a124401c3d Mon Sep 17 00:00:00 2001
From: Dmitry Golovin <dima@golovin.in>
Date: Thu, 5 Dec 2019 00:54:41 +0200
Subject: [PATCH 5/9] x86/boot: kbuild: allow readelf executable to be
 specified

commit eefb8c124fd969e9a174ff2bedff86aa305a7438 upstream.

Introduce a new READELF variable to top-level Makefile, so the name of
readelf binary can be specified.

Before this change the name of the binary was hardcoded to
"$(CROSS_COMPILE)readelf" which might not be present for every
toolchain.

This allows to build with LLVM Object Reader by using make parameter
READELF=llvm-readelf.

Link: https://github.com/ClangBuiltLinux/linux/issues/771
Signed-off-by: Dmitry Golovin <dima@golovin.in>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Makefile                          | 3 ++-
 arch/x86/boot/compressed/Makefile | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index cc72b8472f24..971ed7b03c56 100644
--- a/Makefile
+++ b/Makefile
@@ -414,6 +414,7 @@ STRIP		= $(CROSS_COMPILE)strip
 OBJCOPY		= $(CROSS_COMPILE)objcopy
 OBJDUMP		= $(CROSS_COMPILE)objdump
 OBJSIZE		= $(CROSS_COMPILE)size
+READELF		= $(CROSS_COMPILE)readelf
 PAHOLE		= pahole
 LEX		= flex
 YACC		= bison
@@ -472,7 +473,7 @@ GCC_PLUGINS_CFLAGS :=
 CLANG_FLAGS :=
 
 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
-export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE PAHOLE LEX YACC AWK INSTALLKERNEL
+export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE READELF PAHOLE LEX YACC AWK INSTALLKERNEL
 export PERL PYTHON PYTHON2 PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
 export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
 
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 6b84afdd7538..98aac5b4bdb7 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -102,7 +102,7 @@ vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
 quiet_cmd_check_data_rel = DATAREL $@
 define cmd_check_data_rel
 	for obj in $(filter %.o,$^); do \
-		${CROSS_COMPILE}readelf -S $$obj | grep -qF .rel.local && { \
+		$(READELF) -S $$obj | grep -qF .rel.local && { \
 			echo "error: $$obj has data relocations!" >&2; \
 			exit 1; \
 		} || true; \
-- 
2.28.0.297.g1956fa8f8d-goog


From ac39d2f3b13f640ccf3321d73a8482ff4bc3adbd Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Mon, 6 Jan 2020 17:36:28 +0900
Subject: [PATCH 6/9] kbuild: remove PYTHON2 variable

commit 94f7345b712405b79647a6a4bf8ccbd0d78fa69d upstream.

Python 2 has retired. There is no user of this variable.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Makefile | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 971ed7b03c56..9db9385c335d 100644
--- a/Makefile
+++ b/Makefile
@@ -423,7 +423,6 @@ INSTALLKERNEL  := installkernel
 DEPMOD		= /sbin/depmod
 PERL		= perl
 PYTHON		= python
-PYTHON2		= python2
 PYTHON3		= python3
 CHECK		= sparse
 BASH		= bash
@@ -474,7 +473,7 @@ CLANG_FLAGS :=
 
 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE READELF PAHOLE LEX YACC AWK INSTALLKERNEL
-export PERL PYTHON PYTHON2 PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
+export PERL PYTHON PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
 export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
-- 
2.28.0.297.g1956fa8f8d-goog


From c45a815ff14a684eb7d71875a694ea3e9b3bbaf8 Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Thu, 26 Mar 2020 14:57:18 +0900
Subject: [PATCH 7/9] kbuild: remove AS variable

commit aa824e0c962b532d5073cbb41b2efcd6f5e72bae upstream.

As commit 5ef872636ca7 ("kbuild: get rid of misleading $(AS) from
documents") noted, we rarely use $(AS) directly in the kernel build.

Now that the only/last user of $(AS) in drivers/net/wan/Makefile was
converted to $(CC), $(AS) is no longer used in the build process.

You can still pass in AS=clang, which is just a switch to turn on
the LLVM integrated assembler.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Makefile | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 9db9385c335d..7c5f09904bb5 100644
--- a/Makefile
+++ b/Makefile
@@ -404,7 +404,6 @@ KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
 KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
 
 # Make variables (CC, etc...)
-AS		= $(CROSS_COMPILE)as
 LD		= $(CROSS_COMPILE)ld
 CC		= $(CROSS_COMPILE)gcc
 CPP		= $(CC) -E
@@ -471,7 +470,7 @@ KBUILD_LDFLAGS :=
 GCC_PLUGINS_CFLAGS :=
 CLANG_FLAGS :=
 
-export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
+export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE READELF PAHOLE LEX YACC AWK INSTALLKERNEL
 export PERL PYTHON PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
 export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
@@ -534,7 +533,7 @@ endif
 ifneq ($(GCC_TOOLCHAIN),)
 CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
 endif
-ifeq ($(shell $(AS) --version 2>&1 | head -n 1 | grep clang),)
+ifeq ($(if $(AS),$(shell $(AS) --version 2>&1 | head -n 1 | grep clang)),)
 CLANG_FLAGS	+= -no-integrated-as
 endif
 CLANG_FLAGS	+= -Werror=unknown-warning-option
-- 
2.28.0.297.g1956fa8f8d-goog


From 5a7fd3e996f640114bb6ca27d7303f92af5e4894 Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Wed, 8 Apr 2020 10:36:22 +0900
Subject: [PATCH 8/9] kbuild: replace AS=clang with LLVM_IAS=1

commit 7e20e47c70f810d678d02941fa3c671209c4ca97 upstream.

The 'AS' variable is unused for building the kernel. Only the remaining
usage is to turn on the integrated assembler. A boolean flag is a better
fit for this purpose.

AS=clang was added for experts. So, I replaced it with LLVM_IAS=1,
breaking the backward compatibility.

Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Documentation/kbuild/llvm.rst | 5 ++++-
 Makefile                      | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
index eefbdfa3e4d9..450708534860 100644
--- a/Documentation/kbuild/llvm.rst
+++ b/Documentation/kbuild/llvm.rst
@@ -50,11 +50,14 @@ LLVM Utilities
 LLVM has substitutes for GNU binutils utilities. These can be invoked as
 additional parameters to `make`.
 
-	make CC=clang AS=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
+	make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
 	  OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-size \\
 	  READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\
 	  HOSTLD=ld.lld
 
+Currently, the integrated assembler is disabled by default. You can pass
+`LLVM_IAS=1` to enable it.
+
 Getting Help
 ------------
 
diff --git a/Makefile b/Makefile
index 7c5f09904bb5..552640a22a0c 100644
--- a/Makefile
+++ b/Makefile
@@ -533,7 +533,7 @@ endif
 ifneq ($(GCC_TOOLCHAIN),)
 CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
 endif
-ifeq ($(if $(AS),$(shell $(AS) --version 2>&1 | head -n 1 | grep clang)),)
+ifneq ($(LLVM_IAS),1)
 CLANG_FLAGS	+= -no-integrated-as
 endif
 CLANG_FLAGS	+= -Werror=unknown-warning-option
-- 
2.28.0.297.g1956fa8f8d-goog


From 32509f91e5156984411c4f90502aa32442342e50 Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Wed, 8 Apr 2020 10:36:23 +0900
Subject: [PATCH 9/9] kbuild: support LLVM=1 to switch the default tools to
 Clang/LLVM

commit a0d1c951ef08ed24f35129267e3595d86f57f5d3 upstream.

As Documentation/kbuild/llvm.rst implies, building the kernel with a
full set of LLVM tools gets very verbose and unwieldy.

Provide a single switch LLVM=1 to use Clang and LLVM tools instead
of GCC and Binutils. You can pass it from the command line or as an
environment variable.

Please note LLVM=1 does not turn on the integrated assembler. You need
to pass LLVM_IAS=1 to use it. When the upstream kernel is ready for the
integrated assembler, I think we can make it default.

We discussed what we need, and we agreed to go with a simple boolean
flag that switches both target and host tools:

  https://lkml.org/lkml/2020/3/28/494
  https://lkml.org/lkml/2020/4/3/43

Some items discussed, but not adopted:

- LLVM_DIR

  When multiple versions of LLVM are installed, I just thought supporting
  LLVM_DIR=/path/to/my/llvm/bin/ might be useful.

  CC      = $(LLVM_DIR)clang
  LD      = $(LLVM_DIR)ld.lld
    ...

  However, we can handle this by modifying PATH. So, we decided to not do
  this.

- LLVM_SUFFIX

  Some distributions (e.g. Debian) package specific versions of LLVM with
  naming conventions that use the version as a suffix.

  CC      = clang$(LLVM_SUFFIX)
  LD      = ld.lld(LLVM_SUFFIX)
    ...

  will allow a user to pass LLVM_SUFFIX=-11 to use clang-11 etc.,
  but the suffixed versions in /usr/bin/ are symlinks to binaries in
  /usr/lib/llvm-#/bin/, so this can also be handled by PATH.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com> # build
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Documentation/kbuild/kbuild.rst |  5 +++++
 Documentation/kbuild/llvm.rst   |  8 ++++++--
 Makefile                        | 29 +++++++++++++++++++++++------
 tools/objtool/Makefile          |  6 ++++++
 4 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
index f1e5dce86af7..852ccc551bb3 100644
--- a/Documentation/kbuild/kbuild.rst
+++ b/Documentation/kbuild/kbuild.rst
@@ -262,3 +262,8 @@ KBUILD_BUILD_USER, KBUILD_BUILD_HOST
 These two variables allow to override the user@host string displayed during
 boot and in /proc/version. The default value is the output of the commands
 whoami and host, respectively.
+
+LLVM
+----
+If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
+of GCC and GNU binutils to build the kernel.
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
index 450708534860..c776b6eee969 100644
--- a/Documentation/kbuild/llvm.rst
+++ b/Documentation/kbuild/llvm.rst
@@ -47,8 +47,12 @@ example:
 LLVM Utilities
 --------------
 
-LLVM has substitutes for GNU binutils utilities. These can be invoked as
-additional parameters to `make`.
+LLVM has substitutes for GNU binutils utilities. Kbuild supports `LLVM=1`
+to enable them.
+
+	make LLVM=1
+
+They can be enabled individually. The full list of the parameters:
 
 	make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
 	  OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-size \\
diff --git a/Makefile b/Makefile
index 552640a22a0c..a5237dd861cc 100644
--- a/Makefile
+++ b/Makefile
@@ -394,8 +394,13 @@ HOST_LFS_CFLAGS := $(shell getconf LFS_CFLAGS 2>/dev/null)
 HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS 2>/dev/null)
 HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null)
 
-HOSTCC       = gcc
-HOSTCXX      = g++
+ifneq ($(LLVM),)
+HOSTCC	= clang
+HOSTCXX	= clang++
+else
+HOSTCC	= gcc
+HOSTCXX	= g++
+endif
 KBUILD_HOSTCFLAGS   := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \
 		-fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS) \
 		$(HOSTCFLAGS)
@@ -404,16 +409,28 @@ KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
 KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
 
 # Make variables (CC, etc...)
-LD		= $(CROSS_COMPILE)ld
-CC		= $(CROSS_COMPILE)gcc
 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
+OBJSIZE		= llvm-size
+STRIP		= llvm-strip
+else
+CC		= $(CROSS_COMPILE)gcc
+LD		= $(CROSS_COMPILE)ld
 AR		= $(CROSS_COMPILE)ar
 NM		= $(CROSS_COMPILE)nm
-STRIP		= $(CROSS_COMPILE)strip
 OBJCOPY		= $(CROSS_COMPILE)objcopy
 OBJDUMP		= $(CROSS_COMPILE)objdump
-OBJSIZE		= $(CROSS_COMPILE)size
 READELF		= $(CROSS_COMPILE)readelf
+OBJSIZE		= $(CROSS_COMPILE)size
+STRIP		= $(CROSS_COMPILE)strip
+endif
 PAHOLE		= pahole
 LEX		= flex
 YACC		= bison
diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index ee08aeff30a1..f591c4d1b6fe 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -3,9 +3,15 @@ include ../scripts/Makefile.include
 include ../scripts/Makefile.arch
 
 # always use the host compiler
+ifneq ($(LLVM),)
+HOSTAR	?= llvm-ar
+HOSTCC	?= clang
+HOSTLD	?= ld.lld
+else
 HOSTAR	?= ar
 HOSTCC	?= gcc
 HOSTLD	?= ld
+endif
 AR	 = $(HOSTAR)
 CC	 = $(HOSTCC)
 LD	 = $(HOSTLD)
-- 
2.28.0.297.g1956fa8f8d-goog

Re: LLVM=1 patches for 5.4

[Nick Desaulniers]

On Thu, Aug 20, 2020 at 1:14 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:

Oh, I almost forgot, here's a picture of my cat who helped me by
trying to lay on my keyboard mid-interactive rebase of this series.
https://photos.app.goo.gl/J7CtBJtHmiuzhSfq7
I asked him nicely to move; he proceeded to bite me, and not comply.

>
> Dear stable kernel maintainers,
> Please consider the attached mbox file, which contains 9 patches which
> cherry pick cleanly onto 5.4:
>
> 1. commit fcf1b6a35c16 ("Documentation/llvm: add documentation on
> building w/ Clang/LLVM")
> 2. commit 0f44fbc162b7 ("Documentation/llvm: fix the name of llvm-size")
> 3. commit 63b903dfebde ("net: wan: wanxl: use allow to pass
> CROSS_COMPILE_M68k for rebuilding firmware")
> 4. commit 734f3719d343 ("net: wan: wanxl: use $(M68KCC) instead of
> $(M68KAS) for rebuilding firmware")
> 5. commit eefb8c124fd9 ("x86/boot: kbuild: allow readelf executable to
> be specified")
> 6. commit 94f7345b7124 ("kbuild: remove PYTHON2 variable")
> 7. commit aa824e0c962b ("kbuild: remove AS variable")
> 8. commit 7e20e47c70f8 ("kbuild: replace AS=clang with LLVM_IAS=1")
> 9. commit a0d1c951ef08 ("kbuild: support LLVM=1 to switch the default
> tools to Clang/LLVM")
>
> This series improves/simplifies building kernels with Clang and LLVM
> utilities; it will help the various CI systems testing kernels built
> with Clang+LLVM utilities (in fact I will be pointing to this, if
> accepted, next week at plumbers with those CI system maintainers), and
> we will make immediate use of it in Android (see also:
> https://android-review.googlesource.com/c/platform/prebuilts/clang/host/linux-x86/+/1405387).
> We can always carry it out of tree in Android, but I think the series
> is fairly tame, and would prefer not to.
>
> I only particularly care about 5+8+9 (eefb8c124fd9, 7e20e47c70f8, and
> a0d1c951ef08), but the rest are required for them to cherry-pick
> cleanly.  I don't mind separating those three out, though they won't
> be clean cherry-picks at that point.  It might be good to have
> Masahiro review the series.  If accepted, I plan to wire up test
> coverage of these immediately in
> https://github.com/ClangBuiltLinux/continuous-integration/issues/300.
>
> Most of the above landed in v5.7-rc1, with 94f7345b7124 landing in
> v5.6-rc1 and eefb8c124fd9 landing in v5.5-rc3.
> --
> Thanks,
> ~Nick Desaulniers



-- 
Thanks,
~Nick Desaulniers

Re: LLVM=1 patches for 5.4

[Kees Cook]

On Thu, Aug 20, 2020 at 01:27:32PM -0700, Nick Desaulniers wrote:
> On Thu, Aug 20, 2020 at 1:14 PM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> 
> Oh, I almost forgot, here's a picture of my cat who helped me by
> trying to lay on my keyboard mid-interactive rebase of this series.
> https://photos.app.goo.gl/J7CtBJtHmiuzhSfq7
> I asked him nicely to move; he proceeded to bite me, and not comply.

I think this needs to be an ongoing change to the stable kernel process.
Since such things require documentation, I propose:


diff --git a/Documentation/process/stable-kernel-rules.rst b/Documentation/process/stable-kernel-rules.rst
index 06f743b612c4..928f6f3ce6e2 100644
--- a/Documentation/process/stable-kernel-rules.rst
+++ b/Documentation/process/stable-kernel-rules.rst
@@ -35,6 +35,7 @@ Rules on what kind of patches are accepted, and which ones are not, into the
 Procedure for submitting patches to the -stable tree
 ----------------------------------------------------
 
+ - Preference may be given to submissions featuring pictures of cats. Also dogs.
  - If the patch covers files in net/ or drivers/net please follow netdev stable
    submission guidelines as described in
    :ref:`Documentation/networking/netdev-FAQ.rst <netdev-FAQ>`


> > Dear stable kernel maintainers,
> > Please consider the attached mbox file, which contains 9 patches which
> > cherry pick cleanly onto 5.4:
> >
> > 1. commit fcf1b6a35c16 ("Documentation/llvm: add documentation on
> > building w/ Clang/LLVM")
> > 2. commit 0f44fbc162b7 ("Documentation/llvm: fix the name of llvm-size")
> > 3. commit 63b903dfebde ("net: wan: wanxl: use allow to pass
> > CROSS_COMPILE_M68k for rebuilding firmware")
> > 4. commit 734f3719d343 ("net: wan: wanxl: use $(M68KCC) instead of
> > $(M68KAS) for rebuilding firmware")
> > 5. commit eefb8c124fd9 ("x86/boot: kbuild: allow readelf executable to
> > be specified")
> > 6. commit 94f7345b7124 ("kbuild: remove PYTHON2 variable")
> > 7. commit aa824e0c962b ("kbuild: remove AS variable")
> > 8. commit 7e20e47c70f8 ("kbuild: replace AS=clang with LLVM_IAS=1")
> > 9. commit a0d1c951ef08 ("kbuild: support LLVM=1 to switch the default
> > tools to Clang/LLVM")

And FWIW, "yes please" from me as well. This makes things muuuch easier
to test LTS with Clang.

-- 
Kees Cook

Re: LLVM=1 patches for 5.4

[Greg KH]

On Thu, Aug 20, 2020 at 01:14:36PM -0700, Nick Desaulniers wrote:
> Dear stable kernel maintainers,
> Please consider the attached mbox file, which contains 9 patches which
> cherry pick cleanly onto 5.4:
> 
> 1. commit fcf1b6a35c16 ("Documentation/llvm: add documentation on
> building w/ Clang/LLVM")
> 2. commit 0f44fbc162b7 ("Documentation/llvm: fix the name of llvm-size")
> 3. commit 63b903dfebde ("net: wan: wanxl: use allow to pass
> CROSS_COMPILE_M68k for rebuilding firmware")
> 4. commit 734f3719d343 ("net: wan: wanxl: use $(M68KCC) instead of
> $(M68KAS) for rebuilding firmware")
> 5. commit eefb8c124fd9 ("x86/boot: kbuild: allow readelf executable to
> be specified")
> 6. commit 94f7345b7124 ("kbuild: remove PYTHON2 variable")
> 7. commit aa824e0c962b ("kbuild: remove AS variable")
> 8. commit 7e20e47c70f8 ("kbuild: replace AS=clang with LLVM_IAS=1")
> 9. commit a0d1c951ef08 ("kbuild: support LLVM=1 to switch the default
> tools to Clang/LLVM")
> 
> This series improves/simplifies building kernels with Clang and LLVM
> utilities; it will help the various CI systems testing kernels built
> with Clang+LLVM utilities (in fact I will be pointing to this, if
> accepted, next week at plumbers with those CI system maintainers), and
> we will make immediate use of it in Android (see also:
> https://android-review.googlesource.com/c/platform/prebuilts/clang/host/linux-x86/+/1405387).
> We can always carry it out of tree in Android, but I think the series
> is fairly tame, and would prefer not to.
> 
> I only particularly care about 5+8+9 (eefb8c124fd9, 7e20e47c70f8, and
> a0d1c951ef08), but the rest are required for them to cherry-pick
> cleanly.  I don't mind separating those three out, though they won't
> be clean cherry-picks at that point.  It might be good to have
> Masahiro review the series.  If accepted, I plan to wire up test
> coverage of these immediately in
> https://github.com/ClangBuiltLinux/continuous-integration/issues/300.
> 
> Most of the above landed in v5.7-rc1, with 94f7345b7124 landing in
> v5.6-rc1 and eefb8c124fd9 landing in v5.5-rc3.

All now queued up, thanks.

greg k-h