Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 30 Aug 2022 18:20:09 -0700
From:   Fangrui Song <maskray@google.com>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Nathan Chancellor <nathan@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        nemanja.i.ibm@gmail.com
Subject: Re: [PATCH 2/2] powerpc: remove old code for binutils < 2.25
Message-ID: <20220831012009.4lcw35fqlpygtjys@google.com>
References: <20220830190811.323760-1-masahiroy@kernel.org>
 <20220830190811.323760-2-masahiroy@kernel.org>
 <CAKwvOd=4F-_5+txzbNy4sC8tADGmiEtbVL64CCiAp7nmgyUTnQ@mail.gmail.com>
 <Yw6EoSojRZbj+STd@dev-arch.thelio-3990X>
 <CAKwvOdnzN_-MTNeV5p5rmk1R5B7bftwcWwhXOS2fY1XjJ4u6KA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline
In-Reply-To: <CAKwvOdnzN_-MTNeV5p5rmk1R5B7bftwcWwhXOS2fY1XjJ4u6KA@mail.gmail.com>
Precedence: bulk

On 2022-08-30, Nick Desaulniers wrote:
>On Tue, Aug 30, 2022 at 2:44 PM Nathan Chancellor <nathan@kernel.org> wrote:
>>
>> On Tue, Aug 30, 2022 at 02:13:20PM -0700, Nick Desaulniers wrote:
>> > On Tue, Aug 30, 2022 at 12:10 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>> > >
>> > > The minimum supported version of binutils has been raised to 2.25.1.
>> > > Drop the old code.
>> > >
>> > > PPC is the last user of ld-ifversion. With all the callers removed,
>> > > the macro definition in scripts/Makefile.compiler can go away.
>> > >
>> > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
>> > > ---
>> > >
>> > >  arch/powerpc/Makefile     | 21 ---------------------
>> > >  arch/powerpc/lib/Makefile |  8 --------
>> > >  scripts/Makefile.compiler |  4 ----
>> > >  3 files changed, 33 deletions(-)
>> > >
>> > > diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
>> > > index 02742facf895..fb607758eeca 100644
>> > > --- a/arch/powerpc/Makefile
>> > > +++ b/arch/powerpc/Makefile
>> > > @@ -46,13 +46,7 @@ UTS_MACHINE := $(subst $(space),,$(machine-y))
>> > >  ifdef CONFIG_PPC32
>> > >  KBUILD_LDFLAGS_MODULE += arch/powerpc/lib/crtsavres.o
>> > >  else
>> > > -ifeq ($(call ld-ifversion, -ge, 22500, y),y)
>> > > -# Have the linker provide sfpr if possible.
>> >
>> > ^ Perhaps this comment is still relevant and should not yet be
>> > discarded? Or updated, dropping " if possible".
>> >
>> > Either way:
>> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>>
>> I think we still want this block for ld.lld. Prior to this change,
>> ld.lld would fail the ld-ifversion check and use crtsavres.o. Now, it
>> will try to use '--save-restore-funcs', which it doesn't have support
>> for, breaking the build for at least powernv_defconfig:
>>
>> ld.lld: error: unknown argument '--save-restore-funcs'
>
>Good catch, this should probably be rewritten to use ld-option then.
>
>I wonder what LLD's default behavior is, and if we need a feature request filed?

I have implemented the save/restore functions[1] in ld.lld
(https://reviews.llvm.org/D79977) but do not add --(no-)?save-restore-funcs.
ld.lld's behavior matches GNU ld default: for non-relocatable links,
save/restore functions are synthesized.

ld.bfd --save-restore-funcs changes a relocatable link to define save/restore
functions. Is this behavior sufficiently useful? I don't think the obscure
linker option --save-restore-funcs is used anywhere else (checked with Debian
Code Search).


[1]: In the 64-bit ELF V2 API Specification: Power Architecture, 2.3.3.1. GPR
Save and Restore Functions defines some special functions which may be
referenced by GCC produced assembly (LLVM does not reference them).


>>
>> > > -# There is a corresponding test in arch/powerpc/lib/Makefile
>> > >  KBUILD_LDFLAGS_MODULE += --save-restore-funcs
>> > > -else
>> > > -KBUILD_LDFLAGS_MODULE += arch/powerpc/lib/crtsavres.o
>> > > -endif
>> > >  endif
>> > >
>> > >  ifdef CONFIG_CPU_LITTLE_ENDIAN
>> > > @@ -395,8 +389,6 @@ vdso_prepare: prepare0
>> > >                 $(build)=arch/powerpc/kernel/vdso include/generated/vdso64-offsets.h)
>> > >  endif
>> > >
>> > > -archprepare: checkbin
>> > > -
>> > >  archheaders:
>> > >         $(Q)$(MAKE) $(build)=arch/powerpc/kernel/syscalls all
>> > >
>> > > @@ -411,16 +403,3 @@ else
>> > >         $(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "TASK_CANARY") print $$3;}' include/generated/asm-offsets.h))
>> > >  endif
>> > >  endif
>> > > -
>> > > -PHONY += checkbin
>> > > -# Check toolchain versions:
>> > > -# - gcc-4.6 is the minimum kernel-wide version so nothing required.
>> > > -checkbin:
>> > > -       @if test "x${CONFIG_LD_IS_LLD}" != "xy" -a \
>> > > -               "x$(call ld-ifversion, -le, 22400, y)" = "xy" ; then \
>> > > -               echo -n '*** binutils 2.24 miscompiles weak symbols ' ; \
>> > > -               echo 'in some circumstances.' ; \
>> > > -               echo    '*** binutils 2.23 do not define the TOC symbol ' ; \
>> > > -               echo -n '*** Please use a different binutils version.' ; \
>> > > -               false ; \
>> > > -       fi
>> > > diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
>> > > index 8560c912186d..5eb3971ccb9c 100644
>> > > --- a/arch/powerpc/lib/Makefile
>> > > +++ b/arch/powerpc/lib/Makefile
>> > > @@ -38,14 +38,6 @@ obj-$(CONFIG_PPC32)  += div64.o copy_32.o crtsavres.o
>> > >
>> > >  obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
>> > >
>> > > -# See corresponding test in arch/powerpc/Makefile
>> > > -# 64-bit linker creates .sfpr on demand for final link (vmlinux),
>> > > -# so it is only needed for modules, and only for older linkers which
>> > > -# do not support --save-restore-funcs
>> > > -ifeq ($(call ld-ifversion, -lt, 22500, y),y)
>> > > -extra-$(CONFIG_PPC64)  += crtsavres.o
>> > > -endif
>> > > -
>> > >  obj-$(CONFIG_PPC_BOOK3S_64) += copyuser_power7.o copypage_power7.o \
>> > >                                memcpy_power7.o restart_table.o
>> > >
>> > > diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
>> > > index 94d0d40cddb3..63e7d79dd877 100644
>> > > --- a/scripts/Makefile.compiler
>> > > +++ b/scripts/Makefile.compiler
>> > > @@ -68,7 +68,3 @@ cc-ifversion = $(shell [ $(CONFIG_GCC_VERSION)0 $(1) $(2)000 ] && echo $(3) || e
>> > >  # ld-option
>> > >  # Usage: KBUILD_LDFLAGS += $(call ld-option, -X, -Y)
>> > >  ld-option = $(call try-run, $(LD) $(KBUILD_LDFLAGS) $(1) -v,$(1),$(2),$(3))
>> > > -
>> > > -# ld-ifversion
>> > > -# Usage:  $(call ld-ifversion, -ge, 22252, y)
>> > > -ld-ifversion = $(shell [ $(CONFIG_LD_VERSION)0 $(1) $(2)0 ] && echo $(3) || echo $(4))
>> > > --
>> > > 2.34.1
>> > >
>> >
>> >
>> > --
>> > Thanks,
>> > ~Nick Desaulniers
>
>
>
>-- 
>Thanks,
>~Nick Desaulniers