Cyrix Coma Bug - Analysis

Analysis

What causes the bug is not an interrupt mask, nor are interrupts being explicitly disabled. Instead, an anomaly in the Cyrix's instruction pipeline prevents interrupts from being serviced for the duration of the loop; since the loop never ends, interrupts will never be serviced. The xchg instruction is atomic, meaning that other instructions are not allowed to change the state of the system while it is executed. In order to ensure this atomicity, the designers at Cyrix made the xchg uninterruptible. However, because of pipelining and branch predicting, another xchg enters the pipeline before the previous one completes, leaving the processor in this uninterruptible state forever.

Read more about this topic:  Cyrix Coma Bug

Famous quotes containing the word analysis:

    Whatever else American thinkers do, they psychologize, often brilliantly. The trouble is that psychology only takes us so far. The new interest in families has its merits, but it will have done us all a disservice if it turns us away from public issues to private matters. A vision of things that has no room for the inner life is bankrupt, but a psychology without social analysis or politics is both powerless and very lonely.
    Joseph Featherstone (20th century)

    ... the big courageous acts of life are those one never hears of and only suspects from having been through like experience. It takes real courage to do battle in the unspectacular task. We always listen for the applause of our co-workers. He is courageous who plods on, unlettered and unknown.... In the last analysis it is this courage, developing between man and his limitations, that brings success.
    Alice Foote MacDougall (1867–1945)

    The spider-mind acquires a faculty of memory, and, with it, a singular skill of analysis and synthesis, taking apart and putting together in different relations the meshes of its trap. Man had in the beginning no power of analysis or synthesis approaching that of the spider, or even of the honey-bee; but he had acute sensibility to the higher forces.
    Henry Brooks Adams (1838–1918)