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SubjectRe: [RFC PATCH v2 01/10] lib: vdso: ensure all arches have 32bit fallback
On Mon, Dec 30, 2019 at 1:27 PM Arnd Bergmann <arnd@arndb.de> wrote:
> On Mon, Dec 23, 2019 at 3:31 PM Christophe Leroy <christophe.leroy@c-s.fr> wrote:
> > +static __always_inline
> > +long clock_getres32_fallback(clockid_t _clkid, struct old_timespec32 *_ts)
> > +{
> > + struct __kernel_timespec ts;
> > + int ret = clock_getres_fallback(clock, &ts);
> > +
> > + if (likely(!ret && _ts)) {
> > + _ts->tv_sec = ts.tv_sec;
> > + _ts->tv_nsec = ts.tv_nsec;
> > + }
> > + return ret;
> > +}
>
> Please change these to call __NR_clock_gettime and __NR_clock_getres_time
> instead of __NR_clock_gettime64/__NR_clock_getres_time64 for multiple reasons.
>
> - When doing migration between containers, the vdso may get copied into
> an application running on a kernel that does not support the time64
> variants, and then the fallback fails.
>
> - When CONFIG_COMPAT_32BIT_TIME is disabled, the time32 syscalls
> return -ENOSYS, and the vdso version should have the exact same behavior
> to avoid surprises. In particular an application that checks clock_gettime()
> to see if the time32 are in part of the kernel would get an incorrect result
> here.
>
> arch/arm64/include/asm/vdso/compat_gettimeofday.h already does this,
> I think you can just copy the implementation or find a way to share it.

There was a related discussion on this after a vdso regression on mips,
and I suggested to drop the time32 functions completely from the
vdso when CONFIG_COMPAT_32BIT_TIME is disabled, such as

diff --git a/arch/powerpc/kernel/vdso32/vdso32.lds.S
b/arch/powerpc/kernel/vdso32/vdso32.lds.S
index 00c025ba4a92..605f259fa24c 100644
--- a/arch/powerpc/kernel/vdso32/vdso32.lds.S
+++ b/arch/powerpc/kernel/vdso32/vdso32.lds.S
@@ -145,10 +145,12 @@ VERSION

__kernel_get_syscall_map;
#ifndef CONFIG_PPC_BOOK3S_601
+#ifdef CONFIG_COMPAT_32BIT_TIME
__kernel_gettimeofday;
__kernel_clock_gettime;
__kernel_clock_getres;
__kernel_time;
+#endif
__kernel_get_tbfreq;
#endif
__kernel_sync_dicache;
Any opinions on this? If everyone agrees with that approach, I can
send a cross-architecture patch to do this everywhere. It's probably
best though if Christophe adds that to his series as it touches a lot
of the same files and I would prefer to avoid conflicting changes.

Arnd

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