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Date:   Fri, 27 May 2022 14:18:54 +0800
From:   Leo Yan <leo.yan@linaro.org>
To:     Arnaldo Carvalho de Melo <acme@kernel.org>
Cc:     James Clark <james.clark@arm.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org, broonie@kernel.org,
        german.gomez@arm.com, John Garry <john.garry@huawei.com>,
        Will Deacon <will@kernel.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>, linux-doc@vger.kernel.org
Subject: Re: [PATCH v1 4/6] perf tools: Use dynamic register set for Dwarf
 unwind
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 <Yo+gYbLNnYGOPzGs@kernel.org>
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On Thu, May 26, 2022 at 03:19:54PM -0300, Arnaldo Carvalho de Melo wrote:

[...]

> Too old to support?
> 
>   69     7.19 ubuntu:16.04-x-arm64          : FAIL gcc version 5.4.0 20160609 (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.9)
>     arch/arm64/util/perf_regs.c: In function 'arch__user_reg_mask':
>     arch/arm64/util/perf_regs.c:151:28: error: 'HWCAP_SVE' undeclared (first use in this function)
>       if (getauxval(AT_HWCAP) & HWCAP_SVE)
>                                 ^
>     arch/arm64/util/perf_regs.c:151:28: note: each undeclared identifier is reported only once for each function it appears in
>     /git/perf-5.18.0/tools/build/Makefile.build:139: recipe for target 'util' failed
>     make[5]: *** [util] Error 2
>     /git/perf-5.18.0/tools/build/Makefile.build:139: recipe for target 'arm64' failed
>     make[4]: *** [arm64] Error 2
>     /git/perf-5.18.0/tools/build/Makefile.build:139: recipe for target 'arch' failed
>     make[3]: *** [arch] Error 2
> 
> 
> ⬢[acme@toolbox perf]$ find . -name "*.h" | xargs grep -w HWCAP_SVE
> ./arch/arm64/include/uapi/asm/hwcap.h:#define HWCAP_SVE		(1 << 22)
> ⬢[acme@toolbox perf]$ 

I tested aarch64 GCC-7.4.1 which doesn't support HWCAP_SVE, but
aarch64 GCC-8.3.0 and GCC-9.4.0 support it.

Either we can add below code:

  #ifndef HWCAP_SVE
  #define HWCAP_SVE		(1 << 22)
  #endif

Or directly include header file <.../asm/hwcap.h>.

Not sure which method is preferred.  Maybe the first approach can be
de-couple with Linux kernel code?

Thanks,
Leo