L3: Naming systemsFundamental abstractionsWorld-wide WebWeb namesPC boardSlide 6Abstract bus pictureNamesNaming exampleStep 1: compilationStep 2: linkingStep 3: loadingSophistication: dynamic linkingSummaryL3: Naming systemsFrans Kaashoek6.033 Spring 2007http://web.mit.edu/6.033Fundamental abstractions•Memory•Read/write•Interpreter•Instruction repertoire•Environment•Instruction pointer•Communication links•Send/receive(loop (print (eval (read))))World-wide WebWeb nameshttp://web.mit.edu/6.0333 naming systemshttps://apply.eecs.mit.edu/ex?whatnext=ctlmyfolders&submitted=on&onlyreader=kaashoekname overloading: user query in the nameex is a new interpreterPC boardAbstract bus picture•address is overloaded name with location info•LOAD 1742, R1Names•R1•1742•18.7.22.69•web.mit.edu•http://web.mit.edu/6.033•[email protected]•amsterdam•/mit/6.033/www•foo.c•.. (as in cd .. or ls ..)•wc•(617)253-7149, x37149•021-84-2030Naming examplefoo (…) { int x, y;init()x = bar(…)y = sqrt(x)printf (“answer is %d”, y)}init() { …}0xff00: // foo:…jmp 0xff20 // init…jmp 0xffd0 // bar….jmp 0xffc0 // sqrt…jmp 0xdc00 // printfStep 1: compilationfoo (…) { int x, y;init();x = bar(…);y = sqrt(x);printf (“answer is %d”, y);}init() { …}gcc -c foo.cfoo.o:•Text:0xff00:// foo:jmp +20 // init()…jmp ??? // sqrt….•Symbol table:[init, L, +20][bar, U, ??][sqrt, U, ??][printf, U, ??]Step 2: linkingfoo.o:•Text:0xff00:// foo:jmp +20 // init()…jmp ??? // sqrt….•Symbol table:[init, L, +20][bar, U, ??][sqrt, U, ??][printf, U, ??]•Gcc foo.o bar.o /usr/lib/libm.a /usr/lib/libc.alibm.a (sqrt.o, foo.o): sqrt.o:•Text:0xff00: // sqrt:jmp +20 // init()…•Symbol table:[init, L, +20][sqrt, G, +100]Step 3: loading•Load in memory and adjust addresses:foo.o + bar.o + libm.a + libc.afoo.o + bar.o + libm.a + libc.a0x0232-10xff00: // foo:…jmp 0xff20 // init…jmp 0xffd0 // bar….jmp 0xffc0 // sqrt…jmp 0xdc00 // printfSophistication: dynamic linkingfoo.o + bar.o + libm.a + libc.afoo.o + bar.o + libm.a + libc.a0x0232-1libm.alibc.afoo.o + bar.ofoo.o + bar.o•Resolve names at runtime through indirectiondynamic linkerSummary•Understanding a naming system:•What is the syntax for name?•What are the values?•What is the naming resolution algorithm?•Where does a name’s context
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