linux-kernel - Re: [PATCH 07/17] riscv: vdso: Switch to generic storage implementation

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Message-Id: <137c0594-e178-4c91-bc8b-5f99b3ddb2f0@app.fastmail.com>
Date: Wed, 18 Dec 2024 17:35:31 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 "Conor Dooley" <conor@...nel.org>
Cc: "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
 "Helge Deller" <deller@....de>, "Andy Lutomirski" <luto@...nel.org>,
 "Thomas Gleixner" <tglx@...utronix.de>,
 "Vincenzo Frascino" <vincenzo.frascino@....com>,
 "Anna-Maria Gleixner" <anna-maria@...utronix.de>,
 "Frederic Weisbecker" <frederic@...nel.org>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Catalin Marinas" <catalin.marinas@....com>,
 "Will Deacon" <will@...nel.org>, "Theodore Ts'o" <tytso@....edu>,
 "Jason A . Donenfeld" <Jason@...c4.com>,
 "Paul Walmsley" <paul.walmsley@...ive.com>,
 "Palmer Dabbelt" <palmer@...belt.com>,
 "Albert Ou" <aou@...s.berkeley.edu>,
 "Huacai Chen" <chenhuacai@...nel.org>, "WANG Xuerui" <kernel@...0n.name>,
 "Russell King" <linux@...linux.org.uk>,
 "Heiko Carstens" <hca@...ux.ibm.com>,
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 "Madhavan Srinivasan" <maddy@...ux.ibm.com>,
 "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, linux-parisc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-riscv@...ts.infradead.org, loongarch@...ts.linux.dev,
 linux-s390@...r.kernel.org, linux-mips@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, Linux-Arch <linux-arch@...r.kernel.org>,
 "Nam Cao" <namcao@...utronix.de>
Subject: Re: [PATCH 07/17] riscv: vdso: Switch to generic storage implementation

On Wed, Dec 18, 2024, at 16:46, Thomas Weißschuh wrote:
> On Wed, Dec 18, 2024 at 03:08:28PM +0000, Conor Dooley wrote:
>> On Mon, Dec 16, 2024 at 03:10:03PM +0100, Thomas Weißschuh wrote:

>> Might be a clang thing, allmodconfig with clang doesn't build either.
>
> The proposed generic storage infrastructure currently expects that all
> its users also use HAVE_GENERIC_VDSO.
> I missed rv32 when checking this assumption.
>
> I can add a bunch of ifdefs into the storage code to handle this.
>
> Or we re-add the time vDSO functions which were removed in commit
> d4c08b9776b3 ("riscv: Use latest system call ABI").
> Today there are upstream ports of musl and glibc which can use them.
> (currently musl even tries to use __vdso_clock_gettime() as 64-bit only
> on rv32 due to a copy-and-paste error from its rv64 code)

Adding back __vdso_clock_gettime() wouldn't work on rv32 because there
is no fallback syscall for it, and it wouldn't really help since
there is no existing userspace that uses time32 structures.

> There is precedence in providing 64bit only vDSO functions, for example
> __vdso_clock_gettime64() in arm.
> I do have a small, so far untested, proof-of-concept patch for it.
> This would even be less code than the ifdefs.
>
> What do you think about it?

Yes, simply exposing the normal time64 syscalls through vdso
should be fine. I think this currently works on everything except
rv32 and sparc32, probably because neither of them have actual
users that are able to test.

       Arnd