linux-kernel - Re: [PATCH v3 2/2] perf bench: Add support for 32-bit systems with 64-bit time

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Date:   Wed, 22 Sep 2021 13:27:55 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     André Almeida <andrealmeid@...labora.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Alistair Francis <alistair.francis@...nsource.wdc.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alistair Francis <alistair23@...il.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, linux-perf-users@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Darren Hart <dvhart@...radead.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <alistair.francis@....com>
Subject: Re: [PATCH v3 2/2] perf bench: Add support for 32-bit systems with
 64-bit time_t

On Wed, Sep 22, 2021 at 1:06 AM André Almeida <andrealmeid@...labora.com> wrote:
> Às 05:08 de 21/09/21, Arnd Bergmann escreveu:
> > On Tue, Sep 21, 2021 at 12:47 AM André Almeida
> > <andrealmeid@...labora.com> wrote:
> >>
> >> #if defined(__i386__) || __TIMESIZE == 32
> >> # define NR_gettime64 __NR_clock_gettime64
> >> #else
> >> # define NR_gettime64 __NR_clock_gettime
> >> #endif
> >>
> >> struct timespec64 {
> >>         long long tv_sec;       /* seconds */
> >>         long long tv_nsec;      /* nanoseconds */
> >> };
> >>
> >> int gettime64(clock_t clockid, struct timespec64 *tv)
> >> {
> >>         return syscall(NR_gettime64, clockid, tv);
> >> }
> >>
> >> Then we can just use &timeout at __NR_futex_time64 for 32bit arch and at
> >> __NR_futex for 64bit arch.
> >
> > This is still broken when you disable CONFIG_COMPAT_32BIT_TIME,
> > which disables all system calls that take time32 arguments.
> >
>
> Oh, I think my point was confusing then. My suggestion was to use only
> the futex entry points that accepts time64, and to always use
> clock_gettime that uses time64, for all platforms. Then it will work if
> we disable CONFIG_COMPAT_32BIT_TIME.

Yes, that would be ok. It does require using at least linux-5.1, but we
perf is already sort-of tied to the kernel version.

        Arnd