linux-kernel - Re: what the hell is compat_sys_x86

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Message-ID: <CA+55aFwdxjCjqSOR92GCz4Au9QLekWL_0zumnOyG-sxayDtfzg@mail.gmail.com>
Date:   Sat, 17 Mar 2018 11:19:55 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Dominik Brodowski <linux@...inikbrodowski.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: what the hell is compat_sys_x86_waitpid() for?

On Sat, Mar 17, 2018 at 11:01 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> and tell me what is the difference between those.  In other words, the problem
> with sys32_waitpid() was not that it didn't use proper wrappers - it's that
> it was (and always had been) 100% pointless.

That long long predates Dominik's patches, though.

It clearly is worth fixing, but don't blame Dominik for just
mindlessly converting mindless code.

> For fsck sake, look at the arguments.  waitpid(2) takes pid_t, pointer to int
> and an int.  How the hell could it possibly have required a compat wrapper?

This seems to go all the way back to the original x86_64 merge in
2002, with the original version of arch/x86_64/ia32/sys_ia32.c
containing

   asmlinkage long
   sys32_waitpid(__kernel_pid_t32 pid, unsigned int *stat_addr, int options)
   {
        return sys32_wait4(pid, stat_addr, options, NULL);
   }

and it has only been modified syntactically since.

I suspect the reason is simply that the *regular* waitpid() was writtn
in terms of sys_wait4(), and sys_wait4() needed a compat function, so
then waitpid was basically just carried along.

               Linus