264 lines
8.7 KiB
Python
264 lines
8.7 KiB
Python
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#! /usr/bin/env python
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import sys
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from optparse import OptionParser
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import random
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import math
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def convert(size):
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length = len(size)
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lastchar = size[length-1]
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if (lastchar == 'k') or (lastchar == 'K'):
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m = 1024
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nsize = int(size[0:length-1]) * m
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elif (lastchar == 'm') or (lastchar == 'M'):
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m = 1024*1024
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nsize = int(size[0:length-1]) * m
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elif (lastchar == 'g') or (lastchar == 'G'):
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m = 1024*1024*1024
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nsize = int(size[0:length-1]) * m
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else:
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nsize = int(size)
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return nsize
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def roundup(size):
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value = 1.0
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while value < size:
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value = value * 2.0
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return value
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class OS:
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def __init__(self):
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# 4k phys memory (128 pages)
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self.pageSize = 32
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self.physPages = 128
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self.physMem = self.pageSize * self.physPages
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self.vaPages = 1024
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self.vaSize = self.pageSize * self.vaPages
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self.pteSize = 1
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self.pageBits = 5 # log of page size
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# os tracks
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self.usedPages = []
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self.usedPagesCount = 0
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self.maxPageCount = self.physMem / self.pageSize
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# no pages used (yet)
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for i in range(0, self.maxPageCount):
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self.usedPages.append(0)
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# set contents of memory to 0, too
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self.memory = []
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for i in range(0, self.physMem):
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self.memory.append(0)
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# associative array of pdbr's (indexed by PID)
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self.pdbr = {}
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# mask is 11111 00000 00000 --> 0111 1100 0000 0000
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self.PDE_MASK = 0x7c00
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self.PDE_SHIFT = 10
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# 00000 11111 00000 -> 000 0011 1110 0000
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self.PTE_MASK = 0x03e0
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self.PTE_SHIFT = 5
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self.VPN_MASK = self.PDE_MASK | self.PTE_MASK
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self.VPN_SHIFT = self.PTE_SHIFT
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# grabs the last five bits of a virtual address
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self.OFFSET_MASK = 0x1f
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def findFree(self):
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assert(self.usedPagesCount < self.maxPageCount)
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look = int(random.random() * self.maxPageCount)
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while self.usedPages[look] == 1:
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look = int(random.random() * self.maxPageCount)
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self.usedPagesCount = self.usedPagesCount + 1
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self.usedPages[look] = 1
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return look
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def initPageDir(self, whichPage):
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whichByte = whichPage << self.pageBits
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for i in range(whichByte, whichByte + self.pageSize):
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self.memory[i] = 0x7f
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def initPageTablePage(self, whichPage):
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self.initPageDir(whichPage)
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def getPageTableEntry(self, virtualAddr, ptePage, printStuff):
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pteBits = (virtualAddr & self.PTE_MASK) >> self.PTE_SHIFT
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pteAddr = (ptePage << self.pageBits) | pteBits
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pte = self.memory[pteAddr]
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valid = (pte & 0x80) >> 7
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pfn = (pte & 0x7f)
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if printStuff == True:
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print ' --> pte index:0x%x pte contents:(valid %d, pfn 0x%02x)' % (pteBits, valid, pfn)
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return (valid, pfn, pteAddr)
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def getPageDirEntry(self, pid, virtualAddr, printStuff):
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pageDir = self.pdbr[pid]
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pdeBits = (virtualAddr & self.PDE_MASK) >> self.PDE_SHIFT
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pdeAddr = (pageDir << self.pageBits) | pdeBits
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pde = self.memory[pdeAddr]
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valid = (pde & 0x80) >> 7
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ptPtr = (pde & 0x7f)
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if printStuff == True:
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print ' --> pde index:0x%x pde contents:(valid %d, pfn 0x%02x)' % (pdeBits, valid, ptPtr)
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return (valid, ptPtr, pdeAddr)
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def setPageTableEntry(self, pteAddr, physicalPage):
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self.memory[pteAddr] = 0x80 | physicalPage
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def setPageDirEntry(self, pdeAddr, physicalPage):
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self.memory[pdeAddr] = 0x80 | physicalPage
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def allocVirtualPage(self, pid, virtualPage, physicalPage):
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# make it into a virtual address, as everything uses this (and not VPN)
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virtualAddr = virtualPage << self.pageBits
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(valid, ptPtr, pdeAddr) = self.getPageDirEntry(pid, virtualAddr, False)
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if valid == 0:
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# must allocate a page of the page table now, and have the PD point to it
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assert(ptPtr == 127)
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ptePage = self.findFree()
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self.setPageDirEntry(pdeAddr, ptePage)
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self.initPageTablePage(ptePage)
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else:
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# otherwise, just extract page number of page table page
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ptePage = ptPtr
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# now, look up page table entry too, and mark it valid and fill in translation
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(valid, pfn, pteAddr) = self.getPageTableEntry(virtualAddr, ptePage, False)
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assert(valid == 0)
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assert(pfn == 127)
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self.setPageTableEntry(pteAddr, physicalPage)
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# -2 -> PTE fault, -1 means PDE fault
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def translate(self, pid, virtualAddr):
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(valid, ptPtr, pdeAddr) = self.getPageDirEntry(pid, virtualAddr, True)
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if valid == 1:
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ptePage = ptPtr
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(valid, pfn, pteAddr) = self.getPageTableEntry(virtualAddr, ptePage, True)
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if valid == 1:
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offset = (virtualAddr & self.OFFSET_MASK)
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paddr = (pfn << self.pageBits) | offset
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# print ' --> pfn: %02x offset: %x' % (pfn, offset)
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return paddr
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else:
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return -2
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return -1
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def fillPage(self, whichPage):
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for j in range(0, self.pageSize):
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self.memory[(whichPage * self.pageSize) + j] = int(random.random() * 31)
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def procAlloc(self, pid, numPages):
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# need a PDBR: find one somewhere in memory
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pageDir = self.findFree()
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# print '**ALLOCATE** page dir', pageDir
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self.pdbr[pid] = pageDir
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self.initPageDir(pageDir)
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used = {}
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for vp in range(0, self.vaPages):
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used[vp] = 0
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allocatedVPs = []
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for vp in range(0, numPages):
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vp = int(random.random() * self.vaPages)
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while used[vp] == 1:
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vp = int(random.random() * self.vaPages)
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assert(used[vp] == 0)
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used[vp] = 1
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allocatedVPs.append(vp)
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pp = self.findFree()
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# print '**ALLOCATE** page', pp
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# print ' trying to map vp:%08x to pp:%08x' % (vp, pp)
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self.allocVirtualPage(pid, vp, pp)
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self.fillPage(pp)
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return allocatedVPs
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def dumpPage(self, whichPage):
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i = whichPage
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for j in range(0, self.pageSize):
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print self.memory[(i * self.pageSize) + j],
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print ''
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def memoryDump(self):
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for i in range(0, self.physMem / self.pageSize):
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print 'page %3d:' % i,
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for j in range(0, self.pageSize):
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print '%02x' % self.memory[(i * self.pageSize) + j],
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print ''
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def getPDBR(self, pid):
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return self.pdbr[pid]
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def getValue(self, addr):
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return self.memory[addr]
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# allocate some processes in memory
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# allocate some multi-level page tables in memory
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# make a bit of a mystery:
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# can examine PDBR (PFN of current proc's page directory)
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# can examine contents of any page
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# fill pages with values too
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# ask: when given
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# LOAD VA, R1
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# what will final value will be loaded into R1?
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#
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# main program
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#
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parser = OptionParser()
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parser.add_option('-s', '--seed', default=0, help='the random seed', action='store', type='int', dest='seed')
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parser.add_option('-a', '--allocated', default=64, help='number of virtual pages allocated',
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action='store', type='int', dest='allocated')
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parser.add_option('-n', '--addresses', default=10, help='number of virtual addresses to generate',
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action='store', type='int', dest='num')
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parser.add_option('-c', '--solve', help='compute answers for me', action='store_true', default=False, dest='solve')
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(options, args) = parser.parse_args()
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print 'ARG seed', options.seed
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print 'ARG allocated', options.allocated
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print 'ARG num', options.num
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print ""
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random.seed(options.seed)
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# do the work now
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os = OS()
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used = os.procAlloc(1, options.allocated)
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os.memoryDump()
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print '\nPDBR:', os.getPDBR(1), ' (decimal) [This means the page directory is held in this page]\n'
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for i in range(0, options.num):
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if (random.random() * 100) > 50.0 or i >= len(used):
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vaddr = int(random.random() * 1024 * 32)
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else:
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vaddr = (used[i] << 5) | int(random.random() * 32)
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if options.solve == True:
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print 'Virtual Address %04x:' % vaddr
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r = os.translate(1, vaddr)
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if r > -1:
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print ' --> Translates to Physical Address 0x%03x --> Value: %02x' % (r, os.getValue(r))
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elif r == -1:
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print ' --> Fault (page directory entry not valid)'
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else:
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print ' --> Fault (page table entry not valid)'
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else:
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print 'Virtual Address %04x: Translates To What Physical Address (And Fetches what Value)? Or Fault?' % vaddr
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print ''
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exit(0)
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