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    Subject[PATCH AUTOSEL for 4.9 175/293] MIPS: VDSO: Add implementation of gettimeofday() fallback
    Date
    From: Goran Ferenc <goran.ferenc@imgtec.com>

    [ Upstream commit 0b523a85e134d41f57ddd8c5193bd9f0a5e20b0d ]

    This patch adds gettimeofday_fallback() function that wraps assembly
    invocation of gettimeofday() syscall using __NR_gettimeofday.

    This function is used if pure VDSO implementation gettimeofday()
    does not succeed for any reason. Its imeplementation is enclosed in
    "#ifdef CONFIG_MIPS_CLOCK_VSYSCALL" to be in sync with the similar
    arrangement for __vdso_gettimeofday().

    If syscall invocation via __NR_gettimeofday fails, register a3 will
    be set. So, after the syscall, register a3 is tested and the return
    valuem 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/16640/
    Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    arch/mips/vdso/gettimeofday.c | 24 +++++++++++++++++++++++-
    1 file changed, 23 insertions(+), 1 deletion(-)

    diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofday.c
    index 5f6337545ee2..23305bf6c7a2 100644
    --- a/arch/mips/vdso/gettimeofday.c
    +++ b/arch/mips/vdso/gettimeofday.c
    @@ -20,6 +20,28 @@
    #include <asm/unistd.h>
    #include <asm/vdso.h>

    +#ifdef CONFIG_MIPS_CLOCK_VSYSCALL
    +
    +static __always_inline long gettimeofday_fallback(struct timeval *_tv,
    + struct timezone *_tz)
    +{
    + register struct timezone *tz asm("a1") = _tz;
    + register struct timeval *tv asm("a0") = _tv;
    + register long ret asm("v0");
    + register long nr asm("v0") = __NR_gettimeofday;
    + register long error asm("a3");
    +
    + asm volatile(
    + " syscall\n"
    + : "=r" (ret), "=r" (error)
    + : "r" (tv), "r" (tz), "r" (nr)
    + : "memory");
    +
    + return error ? -ret : ret;
    +}
    +
    +#endif
    +
    static __always_inline long clock_gettime_fallback(clockid_t _clkid,
    struct timespec *_ts)
    {
    @@ -205,7 +227,7 @@ int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)

    ret = do_realtime(&ts, data);
    if (ret)
    - return ret;
    + return gettimeofday_fallback(tv, tz);

    if (tv) {
    tv->tv_sec = ts.tv_sec;
    --
    2.15.1
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