linux-kernel - Re: [PATCH] Fix kernel build with LLVM=1

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Date:   Thu, 31 Mar 2022 15:08:43 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Grigory Vasilyev <h0tc0d3@...il.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yury Norov <yury.norov@...il.com>, Yonghong Song <yhs@...com>,
        Adrian Ratiu <adrian.ratiu@...labora.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] Fix kernel build with LLVM=1

Hi Grigory,

On Fri, Apr 01, 2022 at 12:56:58AM +0300, Grigory Vasilyev wrote:
> The wrong logic is using 1 as a suffix instead of -1.
> So the build script tries to find clang1 file instead of clang.
> 
> GEN     Makefile
> HOSTCC  scripts/basic/fixdep
> /bin/sh: line 1: clang1: command not found
> make[2]: *** [/build/linux/scripts/Makefile.host:95: scripts/basic/fixdep] Error 127
> make[1]: *** [/build/linux/Makefile:564: scripts_basic] Error 2
> make: *** [Makefile:219: __sub-make] Error 2

I am confused by this error, what is your build command? The supported
uses of LLVM= are:

$ make LLVM=1

to use clang, ld.lld, etc.

$ make LLVM=-1

to use clang-1, ld.lld-1, etc.

$ make LLVM=/path/to/

to use /path/to/clang, /path/to/ld.lld, etc.

I do not really understand how based on the current logic you are ending
up with clang1.

$ make -skj"$(nproc)" LLVM=1 distclean defconfig all

works for me here:

$ git show -s --format='%h ("%s")'
478f74a3d808 ("Merge tag 'random-5.18-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random")

$ head -1 init/.main.o.cmd
cmd_init/main.o := clang -Wp,-MMD,init/.main.o.d ...

Please provide more information, as this change should not be necessary.

It could be GNU make related?

$ make --version
GNU Make 4.3
Built for x86_64-pc-linux-gnu
Copyright (C) 1988-2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

> Fixes: b8321ed4a40c("Merge tag 'kbuild-v5.18-v2'")
> 
> Signed-off-by: Grigory Vasilyev <h0tc0d3@...il.com>
> Reported-by: Grigory Vasilyev <h0tc0d3@...il.com>

Normally, you do not add a "Reported-by" for a patch you send, just for
the future.

> ---
>  Makefile                       | 4 ++--
>  tools/scripts/Makefile.include | 4 ++--
>  tools/testing/selftests/lib.mk | 4 ++--
>  3 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 18ecb49f1af6..efca890d4ea3 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -426,8 +426,8 @@ HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null)
>  ifneq ($(LLVM),)
>  ifneq ($(filter %/,$(LLVM)),)
>  LLVM_PREFIX := $(LLVM)
> -else ifneq ($(filter -%,$(LLVM)),)
> -LLVM_SUFFIX := $(LLVM)
> +else ifneq (,$(findstring -, $(LLVM)))
> +LLVM_SUFFIX := $(filter -%, $(LLVM))
>  endif
>  
>  HOSTCC	= $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
> diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
> index 0efb8f2b33ce..c7a56d7f0bad 100644
> --- a/tools/scripts/Makefile.include
> +++ b/tools/scripts/Makefile.include
> @@ -54,8 +54,8 @@ endef
>  ifneq ($(LLVM),)
>  ifneq ($(filter %/,$(LLVM)),)
>  LLVM_PREFIX := $(LLVM)
> -else ifneq ($(filter -%,$(LLVM)),)
> -LLVM_SUFFIX := $(LLVM)
> +else ifneq (,$(findstring -, $(LLVM)))
> +LLVM_SUFFIX := $(filter -%, $(LLVM))
>  endif
>  
>  $(call allow-override,CC,$(LLVM_PREFIX)clang$(LLVM_SUFFIX))
> diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
> index 2a2d240cdc1b..42af066cf39e 100644
> --- a/tools/testing/selftests/lib.mk
> +++ b/tools/testing/selftests/lib.mk
> @@ -3,8 +3,8 @@
>  ifneq ($(LLVM),)
>  ifneq ($(filter %/,$(LLVM)),)
>  LLVM_PREFIX := $(LLVM)
> -else ifneq ($(filter -%,$(LLVM)),)
> -LLVM_SUFFIX := $(LLVM)
> +else ifneq (,$(findstring -, $(LLVM)))
> +LLVM_SUFFIX := $(filter -%, $(LLVM))
>  endif
>  
>  CC := $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
> -- 
> 2.35.1
>