linux-kernel - Re: [PATCH 4/9] posix-clocks: Enable compat syscalls always

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Date:   Mon, 13 Nov 2017 15:26:34 -0800
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     John Stultz <john.stultz@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        y2038 Mailman List <y2038@...ts.linaro.org>
Subject: Re: [PATCH 4/9] posix-clocks: Enable compat syscalls always

On Mon, Nov 13, 2017 at 1:03 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Fri, 10 Nov 2017, Deepa Dinamani wrote:
>>
>> -#ifdef CONFIG_COMPAT
>> -
>>  COMPAT_SYSCALL_DEFINE2(nanosleep, struct compat_timespec __user *, rqtp,
>>                      struct compat_timespec __user *, rmtp)
>>  {
>> @@ -1574,7 +1572,6 @@ COMPAT_SYSCALL_DEFINE2(nanosleep, struct compat_timespec __user *, rqtp,
>>       current->restart_block.nanosleep.compat_rmtp = rmtp;
>>       return hrtimer_nanosleep(&tu, HRTIMER_MODE_REL, CLOCK_MONOTONIC);
>>  }
>> -#endif
>
> So if I'm not missing something important this will make the compat syscall
> define available even for
>
> CONFIG_X86_64=y
> CONFIG_IA32_EMULATION=n
> CONFIG_X86_X32=n
>
> which is wrong because in that configuration we don't have any 32bit
> executable support. So why would we need a compat syscall in that case?

I was thinking that we would switch the meaning of CONFIG_64BIT_TIME
after all architectures have enabled support for 64 bit time_t
syscalls.
After that, I was going to use the config to mean enable only 64 bit
time_t support and so all compat syscalls would have #ifndef
CONFIG_64BIT_TIME around them.
Compat syscalls do not mean compat anymore for these time syscalls as
the data structure is defined in a way that they are the same on 64
bit and 32 bit architectures.

But, you are right. It will leave in compat syscalls when it is not
required now.
I could add a dependency on CONFIG_COMPAT and __BITS_PER_LONG for now
if you prefer. I could introduce additional dependencies later on.

-Deepa