linux-kernel - Re: [PATCH v2] arm64: vdso32: drop -no-integrated-as flag

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Message-ID: <CAKwvOdms0SVJMMLOwK-w=fzsw1FmCSK9qjZ_Syq0A-kRzYkHLQ@mail.gmail.com>
Date:   Thu, 15 Apr 2021 09:52:14 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2] arm64: vdso32: drop -no-integrated-as flag

On Thu, Apr 15, 2021 at 6:31 AM Vincenzo Frascino
<vincenzo.frascino@....com> wrote:
>
>
>
> On 4/14/21 10:45 PM, Nick Desaulniers wrote:
> > Clang can assemble these files just fine; this is a relic from the top
> > level Makefile conditionally adding this. We no longer need --prefix,
> > --gcc-toolchain, or -Qunused-arguments flags either with this change, so
> > remove those too.
> >
> > To test building:
> > $ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
> >   CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 LLVM_IAS=1 \
> >   defconfig arch/arm64/kernel/vdso32/
> >
> > Suggested-by: Nathan Chancellor <nathan@...nel.org>
> > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
>
> The patch looks fine, but I have one question: the kernel requires as a minimum
> Clang/LLVM version 10.0.1. Did you verify that with that version compat vDSOs
> still builds and works correctly?

Hi Vincenzo,
Great question, let's check.
$ cd path/to/llvm-project
$ git checkout origin/release/10.x
$ cd llvm/build && ninja
$ cd path/to/linux
$ b4 am https://lore.kernel.org/lkml/20210413230609.3114365-1-ndesaulniers@google.com/
-o - | git am -3

We can't generally build ARCH=arm64 defconfig with LLVM_IAS=1 with
clang-10, but dropping LLVM_IAS=1 it looks like we can still build
without that.

$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
CROSS_COMPILE_COMPAT=arm-linux-gnueabi- make LLVM=1 -j72 defconfig
clean all
$ ls -l arch/arm64/kernel/vdso32
total 116
-rw-r----- 1 ndesaulniers primarygroup  7534 Apr 14 14:41 Makefile
-rw-r----- 1 ndesaulniers primarygroup   387 Mar 31 10:47 note.c
-rw-r----- 1 ndesaulniers primarygroup  2544 Apr 15 09:48 note.o
-rw-r----- 1 ndesaulniers primarygroup  4552 Apr 15 09:48 vdso.lds
-rw-r----- 1 ndesaulniers primarygroup  1587 Apr  1 12:55 vdso.lds.S
-rw------- 1 ndesaulniers primarygroup  3576 Apr 15 09:48 vdso.so
-rw------- 1 ndesaulniers primarygroup 24380 Apr 15 09:48 vdso.so.dbg
-rwxr-x--- 1 ndesaulniers primarygroup 24380 Apr 15 09:48 vdso.so.raw
-rw-r----- 1 ndesaulniers primarygroup   828 Apr  1 12:55 vgettimeofday.c
-rw-r----- 1 ndesaulniers primarygroup 29084 Apr 15 09:48 vgettimeofday.o

FWIW, clang-10 was missing support for R_AARCH64_PREL32, which affects
building arch/arm64/kvm/hyp/nvhe/hyp-reloc.S.

>
> Otherwise:
>
> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>
>
> > ---
> > Changes V1 -> V2:
> > * Remove --prefix, --gcc-toolchain, COMPAT_GCC_TOOLCHAIN, and
> >   COMPAT_GCC_TOOLCHAIN_DIR as per Nathan.
> > * Credit Nathan with Suggested-by tag.
> > * Remove -Qunused-arguments.
> > * Update commit message.
> >
> >  arch/arm64/kernel/vdso32/Makefile | 8 --------
> >  1 file changed, 8 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> > index 789ad420f16b..3dba0c4f8f42 100644
> > --- a/arch/arm64/kernel/vdso32/Makefile
> > +++ b/arch/arm64/kernel/vdso32/Makefile
> > @@ -10,15 +10,7 @@ include $(srctree)/lib/vdso/Makefile
> >
> >  # Same as cc-*option, but using CC_COMPAT instead of CC
> >  ifeq ($(CONFIG_CC_IS_CLANG), y)
> > -COMPAT_GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE_COMPAT)elfedit))
> > -COMPAT_GCC_TOOLCHAIN := $(realpath $(COMPAT_GCC_TOOLCHAIN_DIR)/..)
> > -
> >  CC_COMPAT_CLANG_FLAGS := --target=$(notdir $(CROSS_COMPILE_COMPAT:%-=%))
> > -CC_COMPAT_CLANG_FLAGS += --prefix=$(COMPAT_GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE_COMPAT))
> > -CC_COMPAT_CLANG_FLAGS += -no-integrated-as -Qunused-arguments
> > -ifneq ($(COMPAT_GCC_TOOLCHAIN),)
> > -CC_COMPAT_CLANG_FLAGS += --gcc-toolchain=$(COMPAT_GCC_TOOLCHAIN)
> > -endif
> >
> >  CC_COMPAT ?= $(CC)
> >  CC_COMPAT += $(CC_COMPAT_CLANG_FLAGS)
> >
>
> --
> Regards,
> Vincenzo



-- 
Thanks,
~Nick Desaulniers