linux-kernel - Re: [patch 7/8] fdmap v2

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Date:	Thu, 7 Jun 2007 14:08:20 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Davide Libenzi <davidel@...ilserver.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2



On Thu, 7 Jun 2007, Eric Dumazet wrote:
> 
> This is a nice idea, but 32/64 compat code is going to hate it :)

It should be fairly simple for 32/64-bit compat code too.

The compat code should just call the compat system call 

> syscall_indirect() would be writen in assembly for each arch, since there is
> no generic syscall table. Thats really a lot of work, especially if we want to
> mess with signal mask, umask ...

No no no. That would be horribly idiotic.

The thing should be 99% generic code, ie we would have

	syscall_indirect(..)
	{
		long retval;

		.. set up signals/flags ..
		retval = arch_syscall_indirect(syscall, args);
		.. unsetup signals/flags ..
		return retval;
	}

	compat_syscall_indirect(..)
	{
		int retval;

		.. set up signals/flags ..
		retval = compat_arch_syscall_indirect(syscall, args);
		.. unsetup signals/flags ..
		return retval;
	}

and the *only* thing that each architecture would need to do is that 
(trivial) arch_syscall_indirect() thing (and the compat version, if 
applicable). And those literally should be generally pretty damn trivial.

The only _subtle_ issue is any system call that actually uses "pt_regs". 
So we'd have to disallow exec/fork/vfork/clone/. They take magic pt_regs 
pointers etc. On x86, for example, the following system calls should *not* 
be things you can do this with:

	asmlinkage int sys_fork(struct pt_regs regs)
	asmlinkage int sys_clone(struct pt_regs regs)
	asmlinkage int sys_vfork(struct pt_regs regs)
	asmlinkage int sys_execve(struct pt_regs regs)
	asmlinkage int sys_vm86old(struct pt_regs regs)
	asmlinkage int sys_vm86(struct pt_regs regs)
	asmlinkage long sys_iopl(unsigned long unused)

because those either take pt_regs, or make pt_regs out of their arguments 
(that "unused" is used to do:

	volatile struct pt_regs * regs = (struct pt_regs *) &unused;

so there is *some* care needed, but other than taking care of this, the 
implementation on x86 should really be totally trivial.

		Linus
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