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Date: Wed, 12 Aug 2009 12:44:11 +0200 From: Andi Kleen <andi@...stfloor.org> To: april <aapril03@...il.com> Cc: linux-kernel@...r.kernel.org Subject: Re: Is compat_sys_ioctl called when both kernel and userland are 64bit ? april <aapril03@...il.com> 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@...ux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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