Re: Is compat_sys_ioctl called when both kernel and userland are 64bit ?

[Andi Kleen]

april <aapril03@xxxxxxxxx> writes:
>
> it seems when a kernel is built to x86_64, whenever a ioctl called
> ,the call flow will be ia32_syscall -->compat_sys_ioctl->compat
> ioctl(if provided)

Only for syscalls throught int 0x80 (or 32bit SYSCALL/SYSENTER), which normally 
only come from 32bit processes. In theory 64bit processes
could use them, but they normally don't.

> but I have some doubt:
>
> My question is:
> 1.  Is compat_sys_ioctl called when both kernel and userland are 64bit
> (suppose I provide those compat ioctl functions)?

No.

>      If not, how kernel knows the driver is 32bit or 64bit?

There are no 32bit drivers on a 64bit kernel, all drivers are 64bit.

For 32bit processes running on a 64bit kernel it depends on the 
entry points (int 0x80 or SYSENTER/SYSCALL)

> 2. when using mmap, the 64bit kernel will return a 64bit address, and
> a userland(32bit) application can only get the lower 32bit,
> it can work when the memory is not large.

The kernel makes sure to only hand out 32bit addresses to 32bit
processes.

-Andi

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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