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    Subject[PATCH AUTOSEL for 4.4 088/162] MIPS: VDSO: Add implementation of clock_gettime() fallback
    Date
    From: Goran Ferenc <goran.ferenc@imgtec.com>

    [ Upstream commit 180902e08f051f72c89ffa366f4e4f7a8e9c753e ]

    This patch adds clock_gettime_fallback() function that wraps assembly
    invocation of clock_gettime() syscall using __NR_clock_gettime.

    This function is used if pure VDSO implementation of clock_gettime()
    does not succeed for any reason. For example, it is called if the
    clkid parameter of clock_gettime() is not one of the clkids listed
    in the switch-case block of the function __vdso_clock_gettime()
    (one such case for clkid is CLOCK_BOOTIME).

    If syscall invocation via __NR_clock_gettime fails, register a3 will
    be set. So, after the syscall, register a3 is tested and the return
    value is negated if it's set.

    Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com>
    Signed-off-by: Miodrag Dinic <miodrag.dinic@imgtec.com>
    Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
    Cc: Douglas Leung <douglas.leung@imgtec.com>
    Cc: James Hogan <james.hogan@imgtec.com>
    Cc: Paul Burton <paul.burton@imgtec.com>
    Cc: Petar Jovanovic <petar.jovanovic@imgtec.com>
    Cc: Raghu Gandham <raghu.gandham@imgtec.com>
    Cc: linux-mips@linux-mips.org
    Cc: linux-kernel@vger.kernel.org
    Patchwork: https://patchwork.linux-mips.org/patch/16639/
    Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    arch/mips/vdso/gettimeofday.c | 25 ++++++++++++++++++++++---
    1 file changed, 22 insertions(+), 3 deletions(-)

    diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofday.c
    index fd7d433970bf..5f6337545ee2 100644
    --- a/arch/mips/vdso/gettimeofday.c
    +++ b/arch/mips/vdso/gettimeofday.c
    @@ -20,6 +20,24 @@
    #include <asm/unistd.h>
    #include <asm/vdso.h>

    +static __always_inline long clock_gettime_fallback(clockid_t _clkid,
    + struct timespec *_ts)
    +{
    + register struct timespec *ts asm("a1") = _ts;
    + register clockid_t clkid asm("a0") = _clkid;
    + register long ret asm("v0");
    + register long nr asm("v0") = __NR_clock_gettime;
    + register long error asm("a3");
    +
    + asm volatile(
    + " syscall\n"
    + : "=r" (ret), "=r" (error)
    + : "r" (clkid), "r" (ts), "r" (nr)
    + : "memory");
    +
    + return error ? -ret : ret;
    +}
    +
    static __always_inline int do_realtime_coarse(struct timespec *ts,
    const union mips_vdso_data *data)
    {
    @@ -207,7 +225,7 @@ int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
    int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
    {
    const union mips_vdso_data *data = get_vdso_data();
    - int ret;
    + int ret = -1;

    switch (clkid) {
    case CLOCK_REALTIME_COARSE:
    @@ -223,10 +241,11 @@ int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
    ret = do_monotonic(ts, data);
    break;
    default:
    - ret = -ENOSYS;
    break;
    }

    - /* If we return -ENOSYS libc should fall back to a syscall. */
    + if (ret)
    + ret = clock_gettime_fallback(clkid, ts);
    +
    return ret;
    }
    --
    2.15.1
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