On Thu, Jan 22, 2026 at 12:31:32PM +0100, Christophe Leroy (CS GROUP) wrote: > Le 22/01/2026 à 12:07, Thomas Weißschuh a écrit : > > 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 > > > > > > > > <[email protected]> > > > > > > > > > > > > > > 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%7C7f1accdfc7ef4d8ea82c08de59a664b8%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639046768343248286%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=7WB%2FCB2ZDhP9bD0GYwEftyRwfDCoRwuQ5uMA98JhfmE%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'm travelling at the moment and won't be able to come with measurement > before next month. But the performance degradation is obvious.
Ack, then I'll send a patch. Thanks for all the information. > With the fix, the function is stackless: (...) > Without the fix, see below, __c_kernel_clock_getres() has to setup a stack > in order to call __cvdso_clock_getres_common(), and in addition we see that > __cvdso_clock_getres_common() is more or less the same size as > __c_kernel_clock_getres() above, so time increase unquestionable. (...) > > 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. > > Well, from the first day we converted powerpc to C time vdso, we've done our > best in order to keep vdso stackless. So I'm not sure it is worth dealing > with the above. Indeed if keeping it as is helps us detect everytime a > change jeoperdises the stackless approach, that's not bad. I was not aware about the stacklessness. Then this should be reason enough. We should get a better system to detect these additional stacks though. I'll think about it a bit more. Note: -finline-stringops=memset would also avoid the issues. Thomas
