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Date:   Mon, 11 Jul 2022 09:34:41 +0100
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Subject: Re: [PATCH v6] coresight: etm4x: avoid build failure with unrolled
 loops
To:     Arnd Bergmann <arnd@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>
Cc:     Mathieu Poirier <mathieu.poirier@linaro.org>,
        David Laight <David.Laight@aculab.com>,
        Tao Zhang <quic_taozha@quicinc.com>,
        Mike Leach <mike.leach@linaro.org>,
        Leo Yan <leo.yan@linaro.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Tom Rix <trix@redhat.com>, coresight@lists.linaro.org,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        clang-built-linux <llvm@lists.linux.dev>
References: <20220708231520.3958391-1-ndesaulniers@google.com>
 <CAK8P3a0x2KJuCjupKuj6XAYUAeF47ZV4bWuEGUQFOcOK_Do2jA@mail.gmail.com>
From:   Suzuki K Poulose <suzuki.poulose@arm.com>
In-Reply-To: <CAK8P3a0x2KJuCjupKuj6XAYUAeF47ZV4bWuEGUQFOcOK_Do2jA@mail.gmail.com>
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On 10/07/2022 20:13, Arnd Bergmann wrote:
> On Sat, Jul 9, 2022 at 1:15 AM Nick Desaulniers <ndesaulniers@google.com> wrote:
> 
>>          ({                                                                      \
>>                  u64 __val;                                                      \
>>                                                                                  \
>> -               if (__builtin_constant_p((offset)))                             \
>> +               if (__is_constexpr((offset)))                                   \
>>                          __val = read_etm4x_sysreg_const_offset((offset));       \
>>                  else                                                            \
>>                          __val = etm4x_sysreg_read((offset), true, (_64bit));    \
>>
> 
> This is clearly better than the current version using
> __builtin_constant_p(), but
> I don't think it's safe in all cases, since there are expressions that
> are constant
> expressions to the compiler but are not valid input to the assembler.
> 
> I would prefer to see this fixed differently, but doing this one first is also
> fine with me:
> 
> Acked-by: Arnd Bergmann <arnd@arndb.de>
> 
>          Arnd


Thanks, I have queued this.

Suzuki