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From:   Florian Weimer <fweimer@redhat.com>
To:     Andrew Waterman <andrew@sifive.com>
Cc:     Palmer Dabbelt <palmer@dabbelt.com>,
        Vineet Gupta <vineetg@rivosinc.com>, stillson@rivosinc.com,
        Paul Walmsley <paul.walmsley@sifive.com>, anup@brainfault.org,
        atishp@atishpatra.org, guoren@kernel.org,
        Conor Dooley <conor.dooley@microchip.com>,
        greentime.hu@sifive.com, vincent.chen@sifive.com,
        andy.chiu@sifive.com, Darius Rad <darius@bluespec.com>,
        arnd@kernel.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org, bjorn@kernel.org,
        libc-alpha@sourceware.org, christoph.muellner@vrull.eu,
        Aaron Durbin <adurbin@rivosinc.com>, linux@rivosinc.com
Subject: Re: RISCV Vector unit disabled by default for new task (was Re:
 [PATCH v12 17/17] riscv: prctl to enable vector commands)
References: <b1dae947-d52a-d28e-5ddc-c1ad6d29828c@rivosinc.com>
        <mhng-84ad9495-ef4b-4343-89ee-dfe45ab69ff7@palmer-ri-x1c9>
        <CA++6G0D8RdjgvzQf-gMdakcF-Jj_PMjP=MBtAbSC0Qcu_WrTTQ@mail.gmail.com>
Date:   Fri, 09 Dec 2022 11:02:57 +0100
In-Reply-To: <CA++6G0D8RdjgvzQf-gMdakcF-Jj_PMjP=MBtAbSC0Qcu_WrTTQ@mail.gmail.com>
        (Andrew Waterman's message of "Thu, 8 Dec 2022 21:42:34 -1000")
Message-ID: <877cz0nbce.fsf@oldenburg.str.redhat.com>
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* Andrew Waterman:

> This suggests that ld.so, early-stage libc, or possibly both will need
> to make this prctl() call, perhaps by parsing the ELF headers of the
> binary and each library to determine if the V extension is used.

If the string functions use the V extension, it will be enabled
unconditionally.  So I don't see why it's okay for libc to trigger this
alleged UAPI change, when the kernel can't do it by default.

Thanks,
Florian