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From: Andrew Jones <drjones@redhat.com>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: pbonzini@redhat.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Subject: Re: [kvm-unit-tests PATCH] arm64: Compile with -mno-outline-atomics for GCC >= 10
Date: Mon, 27 Jul 2020 14:30:31 +0200
Message-ID: <20200727123031.7v52lu23mmhailar@kamzik.brq.redhat.com> (raw)
In-Reply-To: <1bf2eab6-c6df-8b4c-b365-7216e7b9a9d7@arm.com>

On Mon, Jul 27, 2020 at 01:21:03PM +0100, Alexandru Elisei wrote:
> Hi Drew,
> 
> On 7/18/20 2:50 PM, Alexandru Elisei wrote:
> > Hi,
> >
> > On 7/18/20 10:11 AM, Andrew Jones wrote:
> >> On Fri, Jul 17, 2020 at 05:47:27PM +0100, Alexandru Elisei wrote:
> >>> GCC 10.1.0 introduced the -m{,no-}outline-atomics flags which, according to
> >>> man 1 gcc:
> >>>
> >>> "Enable or disable calls to out-of-line helpers to implement atomic
> >>> operations.  These helpers will, at runtime, determine if the LSE
> >>> instructions from ARMv8.1-A can be used; if not, they will use the
> >>> load/store-exclusive instructions that are present in the base ARMv8.0 ISA.
> >>> [..] This option is on by default."
> >>>
> >>> Unfortunately the option causes the following error at compile time:
> >>>
> >>> aarch64-linux-gnu-ld -nostdlib -pie -n -o arm/spinlock-test.elf -T /path/to/kvm-unit-tests/arm/flat.lds \
> >>> 	arm/spinlock-test.o arm/cstart64.o lib/libcflat.a lib/libfdt/libfdt.a /usr/lib/gcc/aarch64-linux-gnu/10.1.0/libgcc.a lib/arm/libeabi.a arm/spinlock-test.aux.o
> >>> aarch64-linux-gnu-ld: /usr/lib/gcc/aarch64-linux-gnu/10.1.0/libgcc.a(lse-init.o): in function `init_have_lse_atomics':
> >>> lse-init.c:(.text.startup+0xc): undefined reference to `__getauxval'
> >>>
> >>> This is happening because we are linking against our own libcflat which
> >>> doesn't implement the function __getauxval().
> >>>
> >>> Disable the use of the out-of-line functions by compiling with
> >>> -mno-outline-atomics if we detect a GCC version greater than 10.
> >>>
> >>> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> >>> ---
> >>>
> >>> Tested with gcc versions 10.1.0 and 5.4.0 (cross-compilation), 9.3.0
> >>> (native).
> >>>
> >>> I've been able to suss out the reason for the build failure from this
> >>> rejected gcc patch [1].
> >>>
> >>> [1] https://patches.openembedded.org/patch/172460/
> >>>
> >>>  arm/Makefile.arm64 | 6 ++++++
> >>>  1 file changed, 6 insertions(+)
> >>>
> >>> diff --git a/arm/Makefile.arm64 b/arm/Makefile.arm64
> >>> index dfd0c56fe8fb..3223cb966789 100644
> >>> --- a/arm/Makefile.arm64
> >>> +++ b/arm/Makefile.arm64
> >>> @@ -9,6 +9,12 @@ ldarch = elf64-littleaarch64
> >>>  arch_LDFLAGS = -pie -n
> >>>  CFLAGS += -mstrict-align
> >>>  
> >>> +# The -mno-outline-atomics flag is only valid for GCC versions 10 and greater.
> >>> +GCC_MAJOR_VERSION=$(shell $(CC) -dumpversion 2> /dev/null | cut -f1 -d.)
> >>> +ifeq ($(shell expr "$(GCC_MAJOR_VERSION)" ">=" "10"), 1)
> >>> +CFLAGS += -mno-outline-atomics
> >>> +endif
> >> How about this patch instead?
> >>
> >> diff --git a/Makefile b/Makefile
> >> index 3ff2f91600f6..0e21a49096ba 100644
> >> --- a/Makefile
> >> +++ b/Makefile
> >> @@ -17,6 +17,11 @@ DESTDIR := $(PREFIX)/share/kvm-unit-tests/
> >>  
> >>  .PHONY: arch_clean clean distclean cscope
> >>  
> >> +# cc-option
> >> +# Usage: OP_CFLAGS+=$(call cc-option, -falign-functions=0, -malign-functions=0)
> >> +cc-option = $(shell if $(CC) -Werror $(1) -S -o /dev/null -xc /dev/null \
> >> +              > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
> >> +
> >>  #make sure env CFLAGS variable is not used
> >>  CFLAGS =
> >>  
> >> @@ -43,12 +48,6 @@ OBJDIRS += $(LIBFDT_objdir)
> >>  #include architecture specific make rules
> >>  include $(SRCDIR)/$(TEST_DIR)/Makefile
> >>  
> >> -# cc-option
> >> -# Usage: OP_CFLAGS+=$(call cc-option, -falign-functions=0, -malign-functions=0)
> >> -
> >> -cc-option = $(shell if $(CC) -Werror $(1) -S -o /dev/null -xc /dev/null \
> >> -              > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
> >> -
> >>  COMMON_CFLAGS += -g $(autodepend-flags) -fno-strict-aliasing -fno-common
> >>  COMMON_CFLAGS += -Wall -Wwrite-strings -Wempty-body -Wuninitialized
> >>  COMMON_CFLAGS += -Wignored-qualifiers -Werror
> >> diff --git a/arm/Makefile.arm64 b/arm/Makefile.arm64
> >> index dfd0c56fe8fb..dbc7524d3070 100644
> >> --- a/arm/Makefile.arm64
> >> +++ b/arm/Makefile.arm64
> >> @@ -9,6 +9,9 @@ ldarch = elf64-littleaarch64
> >>  arch_LDFLAGS = -pie -n
> >>  CFLAGS += -mstrict-align
> >>  
> >> +mno_outline_atomics := $(call cc-option, -mno-outline-atomics, "")
> >> +CFLAGS += $(mno_outline_atomics)
> >> +
> >>  define arch_elf_check =
> >>  	$(if $(shell ! $(OBJDUMP) -R $(1) >&/dev/null && echo "nok"),
> >>  		$(error $(shell $(OBJDUMP) -R $(1) 2>&1)))
> >>
> >>
> >> Thanks,
> >> drew
> > Looks much better than my version. Do you want me to spin a v2 or do you want to
> > send it as a separate patch? If that's the case, I tested the same way I did my
> > patch (gcc 10.1.0 and 5.4.0 for cross-compiling, 9.3.0 native):
> >
> > Tested-by: Alexandru Elisei <alexandru.elisei@arm.com>
> 
> Gentle ping regarding this.
>

Hi Alexandru,

I was on vacation all last week and have been digging myself out of email
today. I'll send this as a proper patch with your T-b later today or
tomorrow.

Thanks,
drew

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  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 16:47 Alexandru Elisei
2020-07-18  9:11 ` Andrew Jones
2020-07-18 13:50   ` Alexandru Elisei
2020-07-27 12:21     ` Alexandru Elisei
2020-07-27 12:30       ` Andrew Jones [this message]
2020-07-27 12:39         ` Alexandru Elisei
2020-07-27 17:25         ` Paolo Bonzini

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