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

["Arnd Bergmann" <arnd@arndb.de>]

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