linux-kernel - Re: [RFC] perf: fix building for ARCv1

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Date:	Sat, 17 Oct 2015 14:19:19 +0000
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Aabid Rushdi <Aabid.Rushdi@...opsys.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
	Darren Hart <dvhart@...ux.intel.com>
Subject: Re: [RFC] perf: fix building for ARCv1

On Saturday 17 October 2015 07:06 PM, Alexey Brodkin wrote:
> Perf uses atomic options and so it is required to have atomics enabled
> in toolchain.
>
> In case of ARC atomics are enabled by default for ARCv2 but disabled for
> ARCv1. Now we explicitly enable atomics for either ARC achitecture
> version so perf could be successfully built.
>
> Currently on attempt to build perf for ARCv1 you'll see tons of:
> ----------------->8-----------------
> undefined reference to `__sync_add_and_fetch_4'
> ----------------->8-----------------
>
> Still note if ARCv1 CPU is configured without LL/SC perf will crash on
> execution once "llock" instruction is attempted to be executed.

Ok this fixes ARCompact - assuming it will have LL/SC. We do have old SoCs w/o
that support.
So what we are saying is that any arch (or a configuration thereof) which doesn't
support atomic r-m-w can't even build perf now - that sucks !

A better way would be to do feature test for __sync_xyz and make atomic_xxx
wrappers call __sync_xyz) vs. an empty stub.
So atleast such arches can build and do "some" perf work !

-Vineet

> Cc: Vineet Gupta <vgupta@...opsys.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>
> ---
>  tools/perf/config/Makefile | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
> index 38a0853..dc7c0a8 100644
> --- a/tools/perf/config/Makefile
> +++ b/tools/perf/config/Makefile
> @@ -47,6 +47,11 @@ ifeq ($(ARCH),arm64)
>    LIBUNWIND_LIBS = -lunwind -lunwind-aarch64
>  endif
>  
> +# Additional ARCH settings for ARC
> +ifeq ($(ARCH),arc)
> +  CFLAGS += -matomic
> +endif
> +
>  ifeq ($(NO_PERF_REGS),0)
>    $(call detected,CONFIG_PERF_REGS)
>  endif

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