Re: [PATCH 2/2] powerpc: remove old code for binutils < 2.25

[Fangrui Song]

On 2022-08-30, Nick Desaulniers wrote:
> On Tue, Aug 30, 2022 at 2:44 PM Nathan Chancellor <nathan@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > > ---
> > > >
> > > >  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@xxxxxxxxxx>
> >
> > 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