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The vDSO basetimes for CLOCK_MONOTONIC and CLOCK_BOOTTIME are stored in
the scaled nanoseconds of tkr_mono, so normalising them requires a
division by NSEC_PER_SEC << shift. That divisor does not fit the u32
parameter of __iter_div_u64_rem(), so update_vdso_time_data() open-codes
the same iterative division twice.
Repeated subtraction is the appropriate form at these two sites because
the quotient never exceeds one. accumulate_nsecs_to_secs() keeps
xtime_nsec below one scaled second, and the offset added to it is a
normalised timespec64 fraction, so the dividend stays below twice the
divisor. That bound holds on every architecture, which matters more here
than the cost of a division on any particular one.
Add __iter_div64_u64_rem(), the u64-divisor counterpart of
__iter_div_u64_rem(), and use it at both sites. Return the quotient as a
u32 for consistency with the u32-divisor variant; the bound above leaves
no use for a wider type.
Store the remainder directly into the basetime, as the coarse clocks
already do. The CLOCK_BOOTTIME copy of the CLOCK_MONOTONIC values then
takes both fields from the same place.
Folding the two open-coded loops into one inlined helper removes 16 bytes
of vsyscall.o text on x86-64 with gcc 13.
No functional change.
Suggested-by: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://patch.msgid.link/20261002153104.1347978-3-zhanxusheng@xiaomi.com
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__iter_div_u64_rem() open-codes an empty asm() to keep the compiler from
turning the subtraction loop into a modulo operation. That is what
OPTIMIZER_HIDE_VAR() is for, so use it and reflow the comment.
The macro lives in linux/compiler.h, which this header did not include.
vdso/math64.h is reached from linux/math64.h, whose includes are
linux/types.h, linux/math.h, asm/div64.h and vdso/math64.h; none of them
guarantees linux/compiler.h. x86 happens to get it through
asm/div64.h -> linux/log2.h, m68k's asm/div64.h only pulls in
asm-generic/div64.h and linux/types.h, so the macro is undeclared there
and the build fails with -Werror=implicit-function-declaration.
Include linux/compiler.h so the header no longer depends on its includer.
This is a no-op for the vDSO, where lib/vdso/gettimeofday.c already gets
it through linux/build_bug.h, and vdso/unaligned.h sets the same
precedent by including linux/compiler_types.h.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20261002153104.1347978-2-zhanxusheng@xiaomi.com
Closes: https://lore.kernel.org/oe-kbuild-all/202609300626.zwNjKaO6-lkp@intel.com/
Closes: https://lore.kernel.org/oe-kbuild-all/202609301300.uAawkHuh-lkp@intel.com/
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Provide mul_u64_u32_add_u64_shr() which is a calculation that will be used
by timekeeping and VDSO.
Place #include <vdso/math64.h> after #include <asm/div64.h> to allow
architecture-specific overrides, at least for the kernel.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240325064023.2997-6-adrian.hunter@intel.com
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The vDSO library should only include the necessary headers required for
a userspace library (UAPI and a minimal set of kernel headers). To make
this possible it is necessary to isolate from the kernel headers the
common parts that are strictly necessary to build the library.
Split math64.h into linux and common headers to make the latter suitable
for inclusion in the vDSO library.
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200320145351.32292-10-vincenzo.frascino@arm.com
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