• Jeremy Fitzhardinge's avatar
    [PATCH] i386: Use %gs as the PDA base-segment in the kernel · f95d47ca
    Jeremy Fitzhardinge authored
    This patch is the meat of the PDA change.  This patch makes several related
    1: Most significantly, %gs is now used in the kernel.  This means that on
       entry, the old value of %gs is saved away, and it is reloaded with
    2: entry.S constructs the stack in the shape of struct pt_regs, and this
       is passed around the kernel so that the process's saved register
       state can be accessed.
       Unfortunately struct pt_regs doesn't currently have space for %gs
       (or %fs). This patch extends pt_regs to add space for gs (no space
       is allocated for %fs, since it won't be used, and it would just
       complicate the code in entry.S to work around the space).
    3: Because %gs is now saved on the stack like %ds, %es and the integer
       registers, there are a number of places where it no longer needs to
       be handled specially; namely context switch, and saving/restoring the
       register state in a signal context.
    4: And since kernel threads run in kernel space and call normal kernel
       code, they need to be created with their %gs == __KERNEL_PDA.
    Signed-off-by: default avatarJeremy Fitzhardinge <jeremy@xensource.com>
    Signed-off-by: default avatarAndi Kleen <ak@suse.de>
    Cc: Chuck Ebbert <76306.1226@compuserve.com>
    Cc: Zachary Amsden <zach@vmware.com>
    Cc: Jan Beulich <jbeulich@novell.com>
    Cc: Andi Kleen <ak@suse.de>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
fork.c 42.2 KB