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, 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)
Date: Fri, 09 Dec 2022 13:32:33 +0100 [thread overview]
Message-ID: <874ju4lpum.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <Y5MoPdYimQtqQvkM@bruce.bluespec.com> (Darius Rad's message of "Fri, 9 Dec 2022 07:21:17 -0500")
* Darius Rad:
> 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.
Failure is usually indicated by an AT_HWCAP or AT_HWCAP2 bit remaining
zero, or perhaps a special CPU register (although that is more unusual).
It's possible to do this differently, but every mid-level startup code
will have to replicate it (the libcs, other run-time environments like
Go, and so on).
Still it's much better than executing the instruction to see if it
traps, so I won't complain too much.
Thanks,
Florian
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next prev parent reply other threads:[~2022-12-09 12:35 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-21 21:43 [PATCH v12 01/17] riscv: Rename __switch_to_aux -> fpu Chris Stillson
2022-09-21 21:43 ` [PATCH v12 02/17] riscv: Extending cpufeature.c to detect V-extension Chris Stillson
[not found] ` <4b6e20fb-d013-0a09-0b74-b6c46e045af3@rivosinc.com>
[not found] ` <CAJF2gTSPoKu_owEb6+MLhAgK5nz2FTRDkTn4qfXF4KyA-XTwvw@mail.gmail.com>
[not found] ` <CAJF2gTT_z96V3kjPtr9hpTq8XRn0x=91wFNPYFFdetAA2u-01Q@mail.gmail.com>
2022-11-04 9:13 ` Conor.Dooley
2022-11-04 18:04 ` Vineet Gupta
2022-09-21 21:43 ` [PATCH v12 03/17] riscv: Add new csr defines related to vector extension Chris Stillson
2023-01-23 11:24 ` Heiko Stübner
2022-09-21 21:43 ` [PATCH v12 04/17] riscv: Add vector feature to compile Chris Stillson
2022-11-07 17:21 ` Björn Töpel
2022-11-08 0:04 ` Vineet Gupta
2022-11-08 7:56 ` Conor Dooley
2022-11-08 17:17 ` Vineet Gupta
2022-11-08 17:22 ` Conor Dooley
2022-11-13 16:16 ` Conor.Dooley
2022-11-15 17:38 ` Vineet Gupta
2022-11-15 22:17 ` Conor Dooley
2022-12-15 0:40 ` Atish Patra
2022-09-21 21:43 ` [PATCH v12 05/17] riscv: Add has_vector/riscv_vsize to save vector features Chris Stillson
2022-09-22 4:23 ` Samuel Holland
2022-09-23 16:27 ` Chris Stillson
2022-09-24 18:01 ` Conor Dooley
2022-11-04 4:10 ` Vineet Gupta
2022-11-04 4:33 ` Vineet Gupta
2022-09-21 21:43 ` [PATCH v12 06/17] riscv: Reset vector register Chris Stillson
2022-11-04 5:01 ` Vineet Gupta
2022-11-04 8:45 ` Guo Ren
2023-01-20 12:20 ` Heiko Stübner
2022-09-21 21:43 ` [PATCH v12 07/17] riscv: Add vector struct and assembler definitions Chris Stillson
2022-11-04 5:13 ` Vineet Gupta
2022-09-21 21:43 ` [PATCH v12 08/17] riscv: Add task switch support for vector Chris Stillson
2022-11-04 22:08 ` Vineet Gupta
2022-09-21 21:43 ` [PATCH v12 09/17] riscv: Add ptrace vector support Chris Stillson
2022-11-08 1:38 ` Vineet Gupta
2022-11-14 20:01 ` Arnd Bergmann
2022-09-21 21:43 ` [PATCH v12 10/17] riscv: Add sigcontext save/restore for vector Chris Stillson
2022-11-09 1:27 ` Vineet Gupta
2022-09-21 21:43 ` [PATCH v12 11/17] riscv: signal: Report signal frame size to userspace via auxv Chris Stillson
2022-09-21 21:43 ` [PATCH v12 12/17] riscv: Add support for kernel mode vector Chris Stillson
2022-09-21 21:43 ` [PATCH v12 13/17] riscv: Add vector extension XOR implementation Chris Stillson
2022-09-21 21:43 ` [PATCH v12 14/17] riscv: Fix a kernel panic issue if $s2 is set to a specific value before entering Linux Chris Stillson
2022-09-21 21:43 ` [PATCH v12 15/17] riscv: Add V extension to KVM ISA allow list Chris Stillson
2022-09-21 21:43 ` [PATCH v12 16/17] riscv: KVM: Add vector lazy save/restore support Chris Stillson
2022-09-21 21:43 ` [PATCH v12 17/17] riscv: prctl to enable vector commands Chris Stillson
2022-12-09 5:16 ` RISCV Vector unit disabled by default for new task (was Re: [PATCH v12 17/17] riscv: prctl to enable vector commands) Vineet Gupta
2022-12-09 6:27 ` Palmer Dabbelt
2022-12-09 7:42 ` Andrew Waterman
2022-12-09 10:02 ` Florian Weimer
2022-12-09 12:21 ` Darius Rad
2022-12-09 12:32 ` Florian Weimer [this message]
2022-12-09 12:42 ` Darius Rad
2022-12-09 13:04 ` Florian Weimer
2022-12-09 17:21 ` Palmer Dabbelt
2022-12-09 19:42 ` Vineet Gupta
2022-12-09 19:58 ` Andrew Waterman
2022-12-13 16:43 ` Darius Rad
2022-12-14 20:07 ` Vineet Gupta
2022-12-14 23:13 ` Samuel Holland
2022-12-15 2:09 ` Darius Rad
2022-12-15 11:48 ` Björn Töpel
2022-12-15 12:28 ` Florian Weimer
2022-12-15 15:33 ` Richard Henderson
2022-12-15 18:57 ` Vineet Gupta
2022-12-15 18:59 ` Andrew Pinski
2022-12-15 19:01 ` Andrew Pinski
2022-12-15 19:56 ` Richard Henderson
2022-12-09 13:58 ` Icenowy Zheng
2023-01-23 11:20 ` [PATCH v12 01/17] riscv: Rename __switch_to_aux -> fpu Heiko Stübner
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