1,In the function of hardwareTrapHandler(int signo, siginfo_t *si, void *context) of libvm.c(ia32)
  the line fo 579, there is "stackLimit - 384"
 line  579  sp = (long unsigned int *)stackLimit - 384;
 line  580 stackLimit -= VM_Constants_STACK_SIZE_GUARD;
 why stacklimit minus 384,
2 also In the function of hardwareTrapHandler(int signo, siginfo_t *si, void *context) of libvm.c(ia32)
line 560 /* Advance ESP to the guard region of the stack.
     * Enables opt compiler to have ESP point to somewhere
     * other than the bottom of the frame at a PEI (see bug 2570).
     *
     * We'll execute the entire code sequence for
     * VM_Runtime.deliverHardwareException et al. in the guard region of the
     * stack to avoid bashing stuff in the bottom opt-frame.
     */
    sp = (long unsigned int *) IA32_ESP(context);
what's the bug of 2570,i can't find it.