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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <72990864-5ec6-1f73-efd9-61b667a172dd@collabora.com>
Date:   Mon, 20 Sep 2021 19:47:44 -0300
From:   André Almeida <andrealmeid@...labora.com>
To:     Alistair Francis <alistair.francis@...nsource.wdc.com>
Cc:     linux-kernel@...r.kernel.org, alistair23@...il.com,
        linux-riscv@...ts.infradead.org, namhyung@...nel.org,
        jolsa@...hat.com, linux-perf-users@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, mark.rutland@....com,
        acme@...nel.org, dave@...olabs.net, dvhart@...radead.org,
        peterz@...radead.org, mingo@...hat.com, tglx@...utronix.de,
        atish.patra@....com, arnd@...db.de,
        Alistair Francis <alistair.francis@....com>
Subject: Re: [PATCH v3 2/2] perf bench: Add support for 32-bit systems with
 64-bit time_t

Hi Alistair,

Às 03:10 de 17/09/21, Alistair Francis escreveu:
> From: Alistair Francis <alistair.francis@....com>
> 
> Some 32-bit architectures (such are 32-bit RISC-V) only have a 64-bit
> time_t and as such don't have the SYS_futex syscall. This patch will
> allow us to use the SYS_futex_time64 syscall on those platforms.
> 

Thanks for your patch! However, I don't think that any futex operation
at perf has timeout. Do you plan to implement a test that use it? Or the
idea is to get this ready for it in case someone want to do so in the
future?

Also, I faced a similar problem with the new futex2 syscalls, that
supports exclusively 64bit timespec. But I took a different approach: I
called __NR_clock_gettime64 for 32bit architectures so it wouldn't
require to convert the struct:

#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 might be a simpler solution to the problem that you are facing but
I'm not entirely sure. Also, futex's selftests do use the timeout
argument and I think that they also won't compile in 32-bit RISC-V, so
maybe we can start from there so we can actually test the timeout
argument and check if it's working.

Thanks,
	André