linux-kernel - Re: [PATCH v1] futex: Add compat_sys_futex

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Date:   Mon, 27 Nov 2023 07:15:59 -0500
From:   Wei Gao <wegao@...e.com>
To:     André Almeida <andrealmeid@...lia.com>
Cc:     tglx@...utronix.de, dvhart@...radead.org,
        linux-kernel@...r.kernel.org, dave@...olabs.net, mingo@...hat.com,
        peterz@...radead.org, Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH v1] futex: Add compat_sys_futex_waitv for 32bit
 compatibility

On Thu, Nov 23, 2023 at 01:09:55PM -0300, André Almeida wrote:
> [+CC Arnd]
> 
> Hi Wei,
> 
> Em 23/11/2023 02:31, Wei Gao escreveu:
> > From: wei gao <wegao@...e.com>
> > 
> > Current implementation lead LTP test case futex_waitv failed when compiled with
> > -m32. This patch add new compat_sys_futex_waitv to handle m32 mode syscall.
> > 
> > The failure reason is futex_waitv in m32 mode will deliver kernel with struct
> > old_timespec32 timeout, but this struct type can not directly used by current
> > sys_futex_waitv implementation.
> > 
> > The new function copy main logic of current sys_futex_waitv, just update parameter
> > type from "struct __kernel_timespec __user *" to "struct old_timespec32 __user *,"
> > and use get_old_timespec32 within the new function to get timeout value.
> > 
> 
> From, what I recall, we don't want to add new syscalls with old_timespec32,
> giving that they will have a limited lifetime. Instead, userspace should be
> able to come up with a 64-bit timespec implementation for -m32.
> 
> Thanks,
> 	André

Just a comment, I have checked the glibc latest code but do not see any implemention(*.c) on
futex_waitv syscall. So normally you have to do syscall directly with __NR_futex_waitv from 
userspace. So i guess glibc-side can not covert this struct correctly currently. Correct me if
any misunderstanding.

Thanks
Wei Gao