linux-kernel - Re: [PATCH 1/2] vdso: sparc: stub out custom vdso implementation

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Message-ID: <0f42d4d49e3b1d9bb1b9b7c323d29e8b1c62c844.camel@physik.fu-berlin.de>
Date: Wed, 23 Jul 2025 13:10:39 +0200
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
 Arnd Bergmann <arnd@...nel.org>
Cc: Andreas Larsson <andreas@...sler.com>, Thomas Gleixner
 <tglx@...utronix.de>,  "David S. Miller" <davem@...emloft.net>, Andy
 Lutomirski <luto@...nel.org>, Vincenzo Frascino	
 <vincenzo.frascino@....com>, shuah <shuah@...nel.org>, Anna-Maria Behnsen	
 <anna-maria@...utronix.de>, Frederic Weisbecker <frederic@...nel.org>, John
 Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>, Catalin
 Marinas	 <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Arnd
 Bergmann	 <arnd@...db.de>, Eric Biggers <ebiggers@...gle.com>,
 sparclinux@...r.kernel.org, 	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] vdso: sparc: stub out custom vdso implementation

Hi Thomas,

On Wed, 2025-07-23 at 12:57 +0200, Thomas Weißschuh wrote:
> On Mon, Jul 07, 2025 at 04:46:37PM +0200, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> > 
> > sparc64 is the only remaining architecture that has its own implementation
> > of the vdso clock_gettime/gettimeofday helpers in place of the generic
> > code. This causes a number of issues:
> > 
> >  - Changes to the vdso interfaces require adding sparc64 specific hacks
> >    even when nothing else needs them
> > 
> >  - The prototypes in <vdso/gettime.h> don't match the function implementation,
> >    and not including that header to avoid the build error from that causes
> >    another warning:
> > 
> >   arch/sparc/vdso/vclock_gettime.c:274:1: error: no previous prototype for '__vdso_clock_gettime' [-Werror=missing-prototypes]
> >     274 | __vdso_clock_gettime(clockid_t clock, struct __kernel_old_timespec *ts)
> >         | ^~~~~~~~~~~~~~~~~~~~
> > 
> >  - Nobody has ever implemented the clock_gettime64() vdso that is required for
> >    32-bit compat tasks
> > 
> >  - The warning about the missing executable-stack flag was missed:
> > 
> >   sparc-linux-ld: warning: arch/sparc/vdso/vdso-note.o: missing .note.GNU-stack section implies executable stack
> >   sparc-linux-ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
> > 
> > Most of the removed code only exists on sparc in order to dynamically
> > patch the vdso based on the presence of the tick vs vtick based
> > clocksource.
> > 
> > Rip out the whole thing and replace it with a minimal stub as we do
> > on parisc and uml. This introduces a small performance regression when
> > using a libc that is aware of the vdso (glibc-2.29 or higher).
> > 
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> FYI I have a series prepared that will move SPARC to the generic vDSO and also
> addresses the problems listed above and mentioned by tglx.
> 
> I'll send it after the merge window.

Great, thanks a lot! Andreas can then retest the patch and see if the performance
hit is measurable or acceptable at all.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913