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    SubjectRe: Calling syscalls from x86-64 kernel results in a crash on Opteron machines
    Date
    On Mon, 13 Sep 2004 18:17:36 +0200
    Andrea Arcangeli <andrea@novell.com> wrote:

    > Hi Constantine,
    >
    > On Mon, Sep 13, 2004 at 06:05:52PM +0300, Constantine Gavrilov wrote:
    > > And BTW, kernel-space applications have their own place even if the
    > > concept seems foreign to you.
    >
    > I avoided to do like i386 that inefficiently calls int 0x80 when you can
    > call sys_read/sys_write etc.. by hand.
    >
    > the syscall is only meaningful if you're not in kernel space. Once
    > you're in kernel space if you ever try to invoke a syscall again (either
    > via int 0x80, syscall, sysenter, call gate, whatever) then you're just
    > going slower than you should for no good reason.
    >
    > The only point of calling int 0x80 and friends is to change mode from
    > user space to kernel space, and you're in kernel space already so you
    > should just call sys_read/sys_write etc.. by hand which will not waste
    > precious cycles and it'll be a lot simpler too.
    >
    > Note also that int 0x80 will bring you into the 32bit emulation layer,
    > the only 64bit entry point is reacheable only via syscall.
    >
    > Hope this helps.


    Actually, the fact that system calls work in kernel space I would consider
    a BUG. The int 0x80 handler should oops or at least kill the offending
    thread for security and robustness reasons.

    --
    Stephen Hemminger mailto:shemminger@osdl.org
    Open Source Development Lab http://developer.osdl.org/shemminger
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