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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