log_trace:
        mflr    %r30
        clrrdi  %r31, %r30, PAGE_SHIFT
        addi    %r31, %r31, (bp_trace - __boot_page)
        std     %r30, 0(%r31)
        mfspr   %r30, SPR_SRR0
        std     %r30, 8(%r31)
        mfspr   %r30, SPR_SRR1
        std     %r30, 16(%r31)
        mfmsr   %r30
        std     %r30, 24(%r31)
        blr