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Date:   Fri, 9 Dec 2022 07:21:17 -0500
From:   Darius Rad <darius@bluespec.com>
To:     Florian Weimer <fweimer@redhat.com>
Cc:     Andrew Waterman <andrew@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Vineet Gupta <vineetg@rivosinc.com>, stillson@rivosinc.com,
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        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)
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On Fri, Dec 09, 2022 at 11:02:57AM +0100, Florian Weimer wrote:
> * 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.
> 

Because the call to enable can fail and userspace needs to deal with that.

// darius