linux-kernel - Re: [PATCH] powerpc/vdso: Provide clock_getres

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Message-ID: <20260122120333-59de004f-2273-49d2-ae93-eb3abe498ab1@linutronix.de>
Date: Thu, 22 Jan 2026 12:07:04 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>
Cc: "Sverdlin, Alexander" <alexander.sverdlin@...mens.com>, 
	"npiggin@...il.com" <npiggin@...il.com>, "luto@...nel.org" <luto@...nel.org>, 
	"maddy@...ux.ibm.com" <maddy@...ux.ibm.com>, "tglx@...nel.org" <tglx@...nel.org>, 
	"mpe@...erman.id.au" <mpe@...erman.id.au>, "vincenzo.frascino@....com" <vincenzo.frascino@....com>, 
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc/vdso: Provide clock_getres_time64()

On Thu, Jan 22, 2026 at 11:58:04AM +0100, Christophe Leroy (CS GROUP) wrote:
> 
> 
> Le 22/01/2026 à 11:49, Thomas Weißschuh a écrit :
> > On Thu, Jan 22, 2026 at 11:27:43AM +0100, Christophe Leroy (CS GROUP) wrote:
> > > Hi Thomas,
> > > 
> > > Le 22/01/2026 à 10:50, Thomas Weißschuh a écrit :
> > > > Hi Alexander,
> > > > 
> > > > On Thu, Jan 22, 2026 at 09:39:09AM +0000, Sverdlin, Alexander wrote:
> > > > > Hi Thomas, Christophe,
> > > > > 
> > > > > On Wed, 2026-01-14 at 08:26 +0100, Thomas Weißschuh wrote:
> > > > > > For consistency with __vdso_clock_gettime64() there should also be a
> > > > > > 64-bit variant of clock_getres(). This will allow the extension of
> > > > > > CONFIG_COMPAT_32BIT_TIME to the vDSO and finally the removal of 32-bit
> > > > > > time types from the kernel and UAPI.
> > > > > > 
> > > > > > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> > > > > 
> > > > > I've bisected this patch to cause the following build failure on my side:
> > > > > 
> > > > >     LDS     arch/powerpc/kernel/vdso/vdso32.lds
> > > > >     VDSO32A arch/powerpc/kernel/vdso/sigtramp32-32.o
> > > > >     VDSO32A arch/powerpc/kernel/vdso/gettimeofday-32.o
> > > > >     VDSO32A arch/powerpc/kernel/vdso/datapage-32.o
> > > > >     VDSO32A arch/powerpc/kernel/vdso/cacheflush-32.o
> > > > >     VDSO32A arch/powerpc/kernel/vdso/note-32.o
> > > > >     VDSO32A arch/powerpc/kernel/vdso/getcpu-32.o
> > > > >     VDSO32A arch/powerpc/kernel/vdso/getrandom-32.o
> > > > >     VDSO32A arch/powerpc/kernel/vdso/vgetrandom-chacha-32.o
> > > > >     VDSO32C arch/powerpc/kernel/vdso/vgettimeofday-32.o
> > > > >     VDSO32C arch/powerpc/kernel/vdso/vgetrandom-32.o
> > > > >     VDSO32A arch/powerpc/kernel/vdso/crtsavres-32.o
> > > > >     VDSO32L arch/powerpc/kernel/vdso/vdso32.so.dbg
> > > > > arch/powerpc/kernel/vdso/vdso32.so.dbg: dynamic relocations are not supported
> > > > > make[2]: *** [arch/powerpc/kernel/vdso/Makefile:79: arch/powerpc/kernel/vdso/vdso32.so.dbg] Error 1
> > > > > make[1]: *** [arch/powerpc/Makefile:388: vdso_prepare] Error 2
> > > > 
> > > > Thanks for the report!
> > > > 
> > > > > Does it ring any bells? What could I try/test?
> > > > 
> > > > Not immediately, but I'll look into it.
> > > > 
> > > > > I'm using gcc-15.2.0 and binutils 2.45.1.
> > > > 
> > > > Is this a toolchain from https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcdn.kernel.org%2Fpub%2Ftools%2Fcrosstool%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C937051154ddf479721f708de59a3e01c%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639046757528646789%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=qkl4zNfg2j%2F24vZV7nQ7LLDtxG0WbgaJc30kjHQZqpk%3D&reserved=0 ?
> > > > Could you also share your configuration?
> > > 
> > > I've just been able to reproduce it with ppc64_defconfig +
> > > CONFIG_CC_OPTIMIZE_FOR_SIZE
> > 
> > Thanks for the hint, no I can reproduce it, too.
> > > 
> > >    VDSO32L arch/powerpc/kernel/vdso/vdso32.so.dbg
> > > arch/powerpc/kernel/vdso/vdso32.so.dbg: dynamic relocations are not
> > > supported
> > > make[2]: *** [arch/powerpc/kernel/vdso/Makefile:79:
> > > arch/powerpc/kernel/vdso/vdso32.so.dbg] Error 1
> > > make[1]: *** [arch/powerpc/Makefile:388: vdso_prepare] Error 2
> > > make: *** [Makefile:248: __sub-make] Error 2
> > > 
> > > I'll investigate
> > 
> > It seems the compiler decides to call memset(), which is not valid from the
> > vDSO. We are are using -ffreestanding. Disabling CONFIG_INIT_STACK_ALL_ZERO
> > fixes the issue. So I guess we should a) figure out why -ffreestanding does
> > not seem to work here and b) exclude the vDSO from the stack initialization
> > logic.
> > 
> 
> Ah, ok.
> 
> Reminds me commit b91c8c42ffdd ("lib/vdso: Force inlining of
> __cvdso_clock_gettime_common()")

Good pointer.

> Problem fixed with:
> 
> diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
> index 95df0153f05ab..4399e143d43a5 100644
> --- a/lib/vdso/gettimeofday.c
> +++ b/lib/vdso/gettimeofday.c
> @@ -421,7 +421,7 @@ static __maybe_unused __kernel_old_time_t
> __cvdso_time(__kernel_old_time_t *time
>  #endif /* VDSO_HAS_TIME */
> 
>  #ifdef VDSO_HAS_CLOCK_GETRES
> -static __maybe_unused
> +static __always_inline
>  bool __cvdso_clock_getres_common(const struct vdso_time_data *vd, clockid_t
> clock,
>  				 struct __kernel_timespec *res)
>  {

Do you want to run the measurements for this one, too and submit a fix?
This should get us past the immediate breakage.

I'll still try to get the stack initialization out of the vDSO.
It might bite us at any time in the future. As these options are meant
to prevent information leaks and the vDSO has no sensitive information in
the first place, we might as well filter them out.


Thomas