加速系统调用
看样子其实是让OS提供一个捷径来执行ugetpid，看样子是绕过内核，而不是加速getpid本身
- 在proc结构体里创建一个
usyscall对象，很多操作和trapframe一样，看这些就行了
$ pgtbltest
ugetpid_test starting
ugetpid_test: OK
pgaccess_test starting
pgtbltest: pgaccess_test failed: incorrect access bits set, pid=3打印page table
全部照搬freework，莫名其妙就过了哈哈
make qemu
qemu-system-riscv64 -machine virt -bios none -kernel kernel/kernel -m 128M -smp 3 -nographic -global virtio-mmio.force-legacy=false -drive file=fs.img,if=none,format=raw,id=x0 -device virtio-blk-device,drive=x0,bus=virtio-mmio-bus.0
xv6 kernel is booting
hart 1 starting
hart 2 starting
page table 0x0000000087f6b000
..0: pte 0x0000000021fd9c01 pa 0x0000000087f67000
.. ..0: pte 0x0000000021fd9801 pa 0x0000000087f66000
.. .. ..0: pte 0x0000000021fda01b pa 0x0000000087f68000
.. .. ..1: pte 0x0000000021fd9417 pa 0x0000000087f65000
.. .. ..2: pte 0x0000000021fd9007 pa 0x0000000087f64000
.. .. ..3: pte 0x0000000021fd8c17 pa 0x0000000087f63000
..255: pte 0x0000000021fda801 pa 0x0000000087f6a000
.. ..511: pte 0x0000000021fda401 pa 0x0000000087f69000
.. .. ..509: pte 0x0000000021fdcc13 pa 0x0000000087f73000
.. .. ..510: pte 0x0000000021fdd007 pa 0x0000000087f74000
.. .. ..511: pte 0x0000000020001c0b pa 0x0000000080007000
init: starting sh
$ QEMU: Terminated