Nature staff discuss some of the week’s top science news.
Try unlimited accessOnly $1 for 4 weeks
。业内人士推荐safew官方版本下载作为进阶阅读
Three microcode cycles for the writeback alone. That's acceptable because segment loads are already expensive multi-cycle operations, and the designers likely expected them to be infrequent -- most programs load their segments once at startup and never touch them again. Page translations happen on every memory access, so the same approach would be ruinous. Hence the fully autonomous hardware walker.
The answer is essentially hardware-level dependency injection. Before calling LD_DESCRIPTOR, the caller saves its desired test constant into a hardware latch using a micro-op called PTSAV (Protection Save). Within LD_DESCRIPTOR, another micro-op called PTOVRR (Protection Override) retrieves and fires the saved test.
Continue reading...