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Date: Thu, 15 Nov 2007 09:02:02 -0800 (PST) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Ulrich Drepper <drepper@...hat.com> cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH 2/4] x86&x86-64 support for sys_indirect [ Ingo, Thomas - see the whole series on linux-kernel ] On Thu, 15 Nov 2007, Ulrich Drepper wrote: > > This part adds support for sys_indirect on x86 and x86-64. The thing is, not all system calls can do this. Some system calls are magic, and don't just take the arguments in registers: they also care about the actual stack pointer and the whole pt_regs struct when returning to user mode. So this does need more infrastructure: some way of marking which system calls cannot be executed indirectly. The magic system calls are things like: - sys_iopl() - this one changes the eflags value restored on iret - execve/clone/vfork() - need direct access to pt_regs - vm86() - does magic with the stack, cares about pt_regs - sigreturn - magic pt_regs accesses again and there may be others I have forgotten about. Calling these system calls from C code will just corrupt the kernel stack, and is a big big no-no. Linus - 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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