• Roland McGrath's avatar
    asmlinkage_protect replaces prevent_tail_call · 54a01510
    Roland McGrath authored
    The prevent_tail_call() macro works around the problem of the compiler
    clobbering argument words on the stack, which for asmlinkage functions
    is the caller's (user's) struct pt_regs.  The tail/sibling-call
    optimization is not the only way that the compiler can decide to use
    stack argument words as scratch space, which we have to prevent.
    Other optimizations can do it too.
    Until we have new compiler support to make "asmlinkage" binding on the
    compiler's own use of the stack argument frame, we have work around all
    the manifestations of this issue that crop up.
    More cases seem to be prevented by also keeping the incoming argument
    variables live at the end of the function.  This makes their original
    stack slots attractive places to leave those variables, so the compiler
    tends not clobber them for something else.  It's still no guarantee, but
    it handles some observed cases that prevent_tail_call() did not.
    Signed-off-by: default avatarRoland McGrath <roland@redhat.com>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
open.c 26.5 KB