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Typically included with each compilation system (e.g., gcc) Invokes preprocessor (cpp), compiler (cc1), assembler (as), and linker (ld). Passes command line arguments to appropriate phases Example: create executable p from m.c and a.c: O/@7 8PBfWhat does a linker do?RMerges object files Merges multiple relocatable (.o) object files into a single executable object Resolves external references As part of the merging process, resolves external references. External reference: reference to a symbol defined in another object file. Relocates symbols Relocates symbols from their relative locations in .o files to new absolute positions in the executable. Updates all references to these symbols to reflect their new positions. References can be in either code or data code: a(); /* reference to symbol a */ data: int *xp=&x; /* reference to symbol x */<N>K)_/>  83|)  )    )  >$ "Cg Why linkers?Modularity Program can be written as a collection of smaller source files, rather than one monolithic mass. Can build libraries of common functions (more on this later) e.g., Math library, standard C library Efficiency Time: Change one source file, compile, and then relink. No need to recompile other source files. Space: Libraries of common functions can be aggregated into a single file... Yet executable files and running memory images contain only code for the functions they actually use.  ' [ '  [ Dh$Executable and Linkable Format (ELF)5Standard binary format for object files Derives from AT&T System V Unix Later adopted by BSD Unix variants and Linux One unified format for Relocatable object files (.o), Executable object files Shared object files (.so) Generic name: ELF binaries Better support for shared libraries than old a.out formats.H-RWH-    2      H ,  EiELF object file formatELF header Magic number, type (.o, exec, .so), machine, byte ordering, etc. Program header table Page size, virtual addresses memory segments (sections), segment sizes. .text section Code .data section Initialized (static) data .bss section Uninitialized (static) data Originally an IBM 704 assembly instruction; think of  Better Save Space Has section header but occupies no space 4 UAZUHZUZUZ UZ AH        Q$$$$*$$, FjELF object file format (cont).symtab section Symbol table Procedure and static variable names Section names and locations .rel.text section Relocation info for .text section Addresses of instructions that will need to be modified in the executable Instructions for modifying. .rel.data section Relocation info for .data section Addresses of pointer data that will need to be modified in the merged executable .debug section Info for symbolic debugging (gcc -g) appears w/ .line as well (src code line mapping)BUMZUZUsZUVZ M      o    Z 3bWGkExample C programHl Merging relocatable object files Im#Relocating symbols & resolving refsSymbols are lexical entities that name functions and variables. Each symbol has a value (typically a memory address). Code consists of symbol definitions and references. References can be either local or external.K7  Jnm.o Relocation infoKoa.o Relocation info (.text).Lpa.o Relocation info (.data).Mq'After relocation & refs. resol. (.text)$(" Nr'After relocation & refs. resol. (.data)$(" OsStrong and weak symbolspProgram symbols are either strong or weak strong: procedures and initialized globals weak: uninitialized globalsL*G*%>M Pt*Linker s symbol rules Rule 1. A strong symbol can only appear once. Rule 2. A weak symbol can be overridden by a strong symbol of the same name. references to the weak symbol resolve to the strong symbol. Rule 3. If there are multiple weak symbols, the linker can pick an arbitrary one.:}<R}<RQuLinker puzzlesRv!Packaging commonly used functionsHow to package functions commonly used by programmers? Math, I/O, memory management, string manipulation, etc. Awkward, given the linker framework so far: Option 1: Put all functions in a single source file Programmers link big object file into their programs Space and time inefficient Option 2: Put each function in a separate source file Programmers explicitly link appropriate binaries into their programs More efficient, but burdensome on the programmer Solution: static libraries (.a archive files) Concatenate related relocatable object files into a single file with an index (called an archive). Enhance linker so that it tries to resolve unresolved external references by looking for the symbols in one or more archives. If an archive member file resolves reference, link into executable.78,4P6v.%78,4  P  6v  %  SwStatic libraries (archives)TxCreating static librariesUyCommonly used librariesBlibc.a (the C standard library) 8 MB archive of 900 object files. I/O, memory allocation, signal handling, string handling, data and time, random numbers, integer math libm.a (the C math library) 1 MB archive of 226 object files. floating point math (sin, cos, tan, log, exp, sqrt, & )  UU\U\  HS VzUsing static librariesLinker s algorithm for resolving external references: Scan .o files and .a files in the command line order. During the scan, keep a list of the current unresolved references. As each new .o or .a file obj is encountered, try to resolve each unresolved reference in the list against the symbols in obj. If any entries in the unresolved list at end of scan, then error. Problem: Command line order matters! Moral: put libraries at the end of the command line. ^6U;Z URZ6; R  ,]W{Loading executable binariesX|Shared libraries&Static libraries still have a few disadvantages: Potential for duplicating common code in multiple exec files e.g., every C program needs the standard C library Potential for duplicating code in the virtual mem. space of many processes Minor bug fixes of system libraries require each application to explicitly relink Solution: Shared libraries (dynamic link libraries, DLLs) whose members are dynamically loaded into memory and linked into an application at run-time. Dynamic linking can occur when exec is first loaded and run. Common case for Linux, handled automatically by ld-linux.so. Dynamic linking can also occur after program has begun. In Linux, this is done explicitly by user with dlopen(). Basis for High-Performance web servers. Shared library routines can be shared by multiple processes.J1U=Z3aZ UZ=a=Z8abZ=a1=3  ~=0 8/ )=Pe ijY}$Dynamically linked shared libraries Z~The complete picture/H[\]^_ ` a b c defghijklmnopqrstuv w!x"i   0` .T3f` T3f3f` 999MMM` lff3f3޲` eoHff33Ҷ` ff!` T3f3fffq` T3f3fff[>?" dd@ ?nPd@ d " @ ` n?" dd@   @@``PR   @ ` `$p>>  ]U ,(  , , s *$ "`0  T Click to edit Master title style! ! , c $ľ "@0  RClick to edit Master text styles Second level Third level Fourth level Fifth level!     S  , c $É ":   AEECS 213 Introduction to Computer Systems Northwestern University2B0(2* 3 3 , Nff??"` , Nff??"` F   ," , Nff??" , Nff??"  , Nff??"  , Nff??"`  , c $̉ "ce  f*"0(2Z , B޽h))? ? T3f3fff[ 0___PPT10.Zj&___PPT92p22 1_aqualab01v  0  0d(  0~ 0 Hff??"A 0 0 "    A Click to edit  0 <,p "   T Click to edit Master title style! !,T   0 "  0 Ttff??"  F 0  0 Twff??"  F 0 ~  0 Hff??"A~  0 Hff??"A  0 RAk B?nwu-seal-gray"@P%  0 c ${ "`0   !Fabin E. Bustamante, Spring 2007H"0(2 3& 3& 3Z 0 B޽h))? ? T3f3fff[80___PPT10.Zj&( 0 d8(  d  d Nyy .   v* a11aa d NDãyy 2 .  x* a11aad d c $ ?  4 d N ͣyy 9 3  RClick to edit Master text styles Second level Third level Fourth level Fifth level!     S d Tѣyy q   v* a11aa d Tyy q2   x* a11aaH d 0ηo~ ? 3380___PPT10.eۡp (     Nyy .   v* a11aa  N4ryy 2 .  x* a11aa  TXٴyy q   v* a11aa  Tܴyy q2   x* a11aaH  0ηo~ ? 3380___PPT10.dz͓ 0L0  $(   r  S p0   r  S 0    H  0޽h ? GGGy___PPT10Y+D=' = @B +E   0 l d   (   ~  s * ,`0     B g ?vL dint x; p1() {} 0    B%g ?AP dint x; p2() {} 0    Bg ?v&  }int x; int y; p1() {} 0 $   Bg ?   Mdouble x; p2() {} 0   BTg ? ^  int x=7; int y=5; p1() {} 0 $  B\g ? *!  Mdouble x; p2() {} 0   B#g ?Q ^ fint x=7; p1() {} 0   B)g ?Q @ dint x; p2() {} 0    B8/g ?l dint x; p1() {} 0    B/g ?pK D p1() {} 0  dB  <D8c?pdB  <D8c?U p\ dB  <D8c? p dB  <D8c?LpLH  0޽h ? GGGy___PPT10Y+D=' = @B +Z   0 y0 $ (  $ ~ $ s *7,`0    $ H<@g ?l   Problems: Efficiency: small change requires complete recompilation Modularity: hard to share common functions (e.g. printf) Solution: Static linker (or linker) 0 t1  0 1  k v'B $  `wawa?o?@ 0 $  f\Ewawa?o?0 ' F Translator 0   $ HpQ8c?P 7 Wm.c0  $ HTA8c?V  ;p0 B $  `wawa?o?    $ HY8c?PL 87 OASCII source file"0   $ H$^8c?P\ h r4Binary executable object file (memory image on disk)"50 5H $ 0޽h ? GGGy___PPT10Y+D=' = @B +D  0 kc@(  (  ( ~ ( s *j,`0   B (  `wawa?o? (  flwawa?o?0  '  G Linker (ld) 0   (  flqwawa?o?@  G Translators 0   ( Hu8c?  Wm.c0  ( Hz8c?Dg Wm.o0  (  f~wawa?o?  G Translators 0    ( Hԁ8c?   Wa.c0   ( H솩8c? : g Wa.o0   ( H̊8c?   ;p0 B  (  `wawa?o?p p B  (  `wawa?o?  B (  `wawa?o?p p B (  `wawa?o?@p p 0 B (  `wawa?o?' R R   ( <8c?'  ,Separately compiled relocatable object files2-0 , w ( <8c?O 8 f  YExecutable object file (contains code and data for all functions defined in m.c and a.c)bZ0 M,MB (  `wawa?o?@  0 H ( 0޽h ? GGGy___PPT10Y+D=' = @B +   0 ;3P, (  , ~ , s *D,`0   ~ , s *,@0   , Bةg ? q@ bass> gcc -O2 -v -o p m.c a.c cpp [args] m.c /tmp/cca07630.i cc1 /tmp/cca07630.i m.c -O2 [args] -o /tmp/cca07630.s as [args] -o /tmp/cca076301.o /tmp/cca07630.s ld -o p [system obj files] /tmp/cca076301.o /tmp/cca076302.o bass> 0  '<1H , 0޽h ? GGGy___PPT10Y+D=' = @B +   0 `0 <(  0 ~ 0 s *ȩ,`0   ~ 0 s *ɩ,@0  H 0 0޽h ? GGGy___PPT10Y+D=' = @B +   0 p4 <(  4 ~ 4 s *`ߩ,`0   ~ 4 s *,@0  H 4 0޽h ? GGGy___PPT10Y+D=' = @B +   0 8 <(  8 ~ 8 s *,`0   ~ 8 s *(,@0  H 8 0޽h ? GGGy___PPT10Y+D=' = @B +    0   < n (  < ~ < s *p,`0   ~ < s *,@    < <t I8c?`pP H ELF header" 0    < <I8c?Pp m/Program header table (required for executables)"00 0  < <DI8c?p Y .text section00    < <I8c?p Y .data section00    < <I8c?p z .bss section0 0      < <$I8c?p  g.symtab"0    < <\)I8c? p  h.rel.txt" 0     < <.I8c? pp  i .rel.data" 0     < <<3I8c?p p`  D.debug"0    < <6I8c?` p  0Section header table (required for relocatables)"10 1 #  < H08c?P ;   huninitialized data 0   %H HxA8c?* w  b.bss 0 jB &H BD)? j j jB 'H BD)?j j jB (H BD)? j j  )H <E8c?K;  G system code 0  H H 0޽h ? GGGy___PPT10Y+D=' = @B +)  0 OGL (  L ~ L s *Q,`0   ~ L s *R,@0  " L BSg ?P  6int e=7; int main() { int r = a(); exit(0); }  70 76   L HZg ?P ]m.c$0  L H_g ? A  ]a.c$0  L B|cg ? o  Rextern int e; int *ep=&e; int x=15; int y; int a() { return *ep+x+y; }  S0 Sz >0  L  f,$D 0  L  <0m8c?>  `Def of local symbol e.0 rB  L BD8c?0n00 0z > ?  L  f `g,$D 0,  L  Hq8c? ? 2Ref to external symbol exit (defined in libc.so)<30 **rB  L BD8c?`>  z =   L  @`HH ,$D 0 L  Hx8c? =   bRef to external symbol e.0 rB L BD8c? P  z    L  ` ,$D 0 L  H4.8c?   Def of local symbol ep .0 rB L BD8c?@ ^ z p~ P# L   @0s ,$D 0 L  <|8c?  P# Defs of local symbols x and yJ 0 rB L BD8c?p~  z   L  F ,$D 0 L  <H8c?o Refs of local symbols ep,x,y.0 rB L BD8c? z  ^ & L   gN,$D 0 L  H8c? & oDef of local symbol a <0 rB L BD8c?P ^ ?z ~ .  L    ,$D 0 L  H@8c?] .  cRef to external symbol a.0 rB L BD8c? ~ @N H L 0޽h ? GGG*"___PPT10+$D' = @B D' = @BA?%,( < +O%,( < +D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*L %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*L %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<* L %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*L %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*L %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*L %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*L %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*L %(+   0    P  (  P ~ P s *8,`0    P Bpg ?010  /Disassembly of section .text: 00000000
: 00000000
: 0: 55 pushl %ebp 1: 89 e5 movl %esp,%ebp 3: e8 fc ff ff ff call 4 4: R_386_PC32 a 8: 6a 00 pushl $0x0 a: e8 fc ff ff ff call b b: R_386_PC32 exit f: 90 nop 0  /2 /#\ Z]G P Bx̭g ?@ ~ EDisassembly of section .data: 00000000 : 0: 07 00 00 00 @F0 8 ,> P Hӭ8c?` msource: objdump 0 < P B׭g ?0z 6int e=7; int main() { int r = a(); exit(0); } :70 06   P Hx߭g ?M86 [m.c"0 d P <g ?pd  P <g ?ph H P 0޽h ? GGGy___PPT10Y+D=' = @B +K   0 r j T  (  T ~ T s *,`0    T Hhg ?v_ [a.c"0  T B`g ??  Rextern int e; int *ep=&e; int x=15; int y; int a() { return *ep+x+y; } S0 S T 61?0P0F +3Disassembly of section .text: 00000000 : 0: 55 pushl %ebp 1: 8b 15 00 00 00 movl 0x0,%edx 6: 00 3: R_386_32 ep 7: a1 00 00 00 00 movl 0x0,%eax 8: R_386_32 x c: 89 e5 movl %esp,%ebp e: 03 02 addl (%edx),%eax 10: 89 ec movl %ebp,%esp 12: 03 05 00 00 00 addl 0x0,%eax 17: 00 14: R_386_32 y 18: 5d popl %ebp 19: c3 ret @40 c  +JHBP   ]%d T <g ?d T <g ? d T <g ? ` H T 0޽h ? GGGy___PPT10Y+D=' = @B +  0 X v(  X ~ X s *(,`0    X H|*g ?v_ [a.c"0  X B/g ??  Rextern int e; int *ep=&e; int x=15; int y; int a() { return *ep+x+y; } S0 S X 681?0 wDisassembly of section .data: 00000000 : 0: 00 00 00 00 0: R_386_32 e 00000004 : 4: 0f 00 00 00`0 9 $t+6d X <g ?8`H X 0޽h ? GGGy___PPT10Y+D=' = @B +  0 \ :(  \ ~ \ s *|M,`0   | \ Bc1?h .08048530
: 8048530: 55 pushl %ebp 8048531: 89 e5 movl %esp,%ebp 8048533: e8 08 00 00 00 call 8048540 8048538: 6a 00 pushl $0x0 804853a: e8 35 ff ff ff call 8048474 <_init+0x94> 804853f: 90 nop 08048540 : 8048540: 55 pushl %ebp 8048541: 8b 15 1c a0 04 movl 0x804a01c,%edx 8048546: 08 8048547: a1 20 a0 04 08 movl 0x804a020,%eax 804854c: 89 e5 movl %esp,%ebp 804854e: 03 02 addl (%edx),%eax 8048550: 89 ec movl %ebp,%esp 8048552: 03 05 d0 a3 04 addl 0x804a3d0,%eax 8048557: 08 8048558: 5d popl %ebp 8048559: c3 ret /0  V ) )T2"6!?7"H3"  "H'H \ 0޽h ? GGGy___PPT10Y+D=' = @B +  0  ` R(  ` ~ ` s *z,`0   " ` 64|1?   Disassembly of section .data: 0804a018 : 804a018: 07 00 00 00 0804a01c : 804a01c: 18 a0 04 08 0804a020 : 804a020: 0f 00 00 00@0  VbF5o  ` Bg ? j 6int e=7; int main() { int r = a(); exit(0); } 70 76   ` Hg ?=8& [m.c"0  ` Hpg ?v  [a.c"0  ` BHg ?v B Rextern int e; int *ep=&e; int x=15; int y; int a() { return *ep+x+y; } S0 SH ` 0޽h ? GGGy___PPT10Y+D=' = @B +   0   0d t (  d ~ d s *|,`0   ~ d s *T,@0   d Bg ?   ~int foo=5; p1() { }"0 $ d BPg ?: `  |int foo; p2() { }"0 $  d HĴg ?  Bp1.c"0  d HTg ?:  Bp2.c"0  d H8c? T  @strong0 jB  d @ BD8c?    d H8c?@ >weak0 jB  d @ BD8c?@@@  d HĮ8c?   @strong0 jB  d @ BD8c? 0  d HȮ8c? @strong0 jB d @ BD8c?@0@H d 0޽h ? GGGy___PPT10Y+D=' = @B +  0 @h <(  h ~ h s *8خ,`0   ~ h s *ٮ,@0  H h 0޽h ? GGGy___PPT10Y+D=' = @B +J"  0 h`Pl (  l ~ l s *ݮ,`0    l B0g ?vn dint x; p1() {} 0   l Bg ?Ar dint x; p2() {} 0   l Bg ?>vH  }int x; int y; p1() {} 0 $  l Bg ?B Mdouble x; p2() {} 0  l B4g ? ^  int x=7; int y=5; p1() {} 0 $ l Bg ? C  Mdouble x; p2() {} 0   l Bg ?s ^  fint x=7; p1() {} 0   l B g ?s @  dint x; p2() {} 0    l B g ? dint x; p1() {} 0    l B\g ?K D p1() {} 0  ,  l H8c? ,$D 0 (Link time error: two strong symbols (p1)<)0 % l H8c?} h,$D 0 YReferences to x will refer to the same uninitialized int. Is this what you really want?<Z0 J) $f l HP8c? h,$D 0 *Writes to x in p2 might overwrite y! Evil!t+0  g l H|-8c? H ,$D 0 +Writes to x in p2 will overwrite y! Nasty! t,0   (z  U l  \ U,$D 0N l  H48c?@ pNightmare scenario: two identical weak structs, compiled by different compilers with different alignment rules.  q0 q'CH l  H:8c?  U| ,$D 0 <References to x will refer to the same initialized variable.<=0 .B l <D8c?p,$D 0dB l <D8c?w p~ dB l <D8c? p dB l <D8c?npnH l 0޽h ? GGG  ___PPT10b +Df ' = @B D! ' = @BA?%,( < +O%,( < +DA' =%(D' =%(D' =A@BBBB0B%(D' =1:Bvisible*o3>+B#style.visibility<* l %(DA' =%(D' =%(D' =A@BBBB0B%(D' =1:Bvisible*o3>+B#style.visibility<*l %(DA' =%(D' =%(D' =A@BBBB0B%(D' =1:Bvisible*o3>+B#style.visibility<*l %(DA' =%(D' =%(D' =A@BBBB0B%(D' =1:Bvisible*o3>+B#style.visibility<*l %(D4' =%(D' =%(D' =4@BBBB%(D' =1:Bvisible*o3>+B#style.visibility<*l %(++0+ l 0 ++0+l 0 ++0+l 0 ++0+l 0 +  0 `p <(  p ~ p s *G,`0   ~ p s *H,@0  H p 0޽h ? GGGy___PPT10Y+D=' = @B +  0 pt (  t ~ t s *4H,`0   B t  `wawa?o? t  fVwawa?o?@ R Translator, 0   t H\8c? >p1.c0  t H_8c?`G >p1.o0  t  fhdwawa?o?`  R Translator, 0   t H\h8c?4  >p2.c0   t Hl8c?`4 G >p2.o0 B  t  `wawa?o?B  t  `wawa?o?B  t  `wawa?o?B  t  `wawa?o? B t  `wawa?o?  t Hp8c?` G Zlibc.a0 B t @  `wawa?o?  0 t <u8c?@  Pstatic library (archive) of relocatable object files concatenated into one file.6Q0 P * t <T{8c?/ 7  8jexecutable object file (only contains code and data for libc functions that are called from p1.c and p2.c)k0 7 8/ t <8c? pP< Further improves modularity and efficiency by packaging commonly used functions [e.g., C standard library (libc), math library (libm)] Linker selectively only the .o files in the archive that are actually needed by the program.t0 k!?,kb t  fwawa?o?P   G Linker (ld) 0   t H@8c? z  ;p0 B t  `wawa?o?  H t 0޽h ? GGGy___PPT10Y+D=' = @B +  0 x (  x ~ x s *,`0   B x  `wawa?o?`` x  f袰wawa?o? R Translator, 0   x H\8c?0 Zatoi.c0  x H8c?w Zatoi.o0  x  fwawa?o?0  R Translator, 0   x HX8c?0 \printf.c 0    x Hd8c? w \printf.o 0  B  x  `wawa?o?B  x  `wawa?o?``B  x  `wawa?o?B  x  `wawa?o?~ x H 8c? X  Zlibc.a0 B x @  `wawa?o?W w  x  f(İwawa?o?  u Archiver (ar) 0 $ x HdȰ8c?  ?... 0  x  f|wawa?o?p  R Translator, 0   x HѰ8c?7p  \random.c 0   x Hΰ8c?| ~ \random.o 0  B x  `wawa?o? B x  `wawa?o? B x  `wawa?o?W``w x Hڰ8c?   Zar rs libc.a \ atoi.o printf.o & random.o$.0 .lB x  `wawa?o?  J x <8c?  fArchiver allows incremental updates: Recompile function that changes and replace .o file in archive.B&0 A1 &A_ x <8c?   dC standard library60 H x 0޽h ? GGGy___PPT10Y+D=' = @B +  0 | >(  | ~ | s *@,`0   ~ | s *,@0  b | B\g ?  f % ar -t /usr/lib/libc.a | sort & fork.o & fprintf.o fpu_control.o fputc.o freopen.o fscanf.o fseek.o fstab.o &  y0 y     | Bg ? l  % ar -t /usr/lib/libm.a | sort & e_acos.o e_acosf.o e_acosh.o e_acoshf.o e_acoshl.o e_acosl.o e_asin.o e_asinf.o e_asinl.o &  0         H | 0޽h ? GGGy___PPT10Y+D=' = @B +q  0  ((   ~  s *h$,`0   ~  s *$,@0    B&? Wf rbass> gcc -L. libtest.o -lmine bass> gcc -L. -lmine libtest.o libtest.o: In function `main': libtest.o(.text+0x4): undefined reference to `libfun'  0    EH  0޽h ? GGGy___PPT10Y+D=' = @B +  0 +# (   ~  s *C,`0     <E8c? H ELF header" 0    <I8c?` m/Program header table (required for executables)"00 0  <|M8c?`P K .text section"0   <R8c?P@ K .data section"0   <LV8c?@0  l .bss section" 0     <\8c?0   g.symtab"0   <|`8c?   i .rel.text" 0    < jB  BD8c? jB  BD8c?  jB  BD8c?   H08c?p5 k-Executable object file for example program p".0 .  H8c?` [ I Process image 0   Hp8c?" F 0x08048494 0    Bp8c?0   Zinit and shared lib segments"0   HP8c?p"0 F 0x080483e0 0    H8c?l @ j Virtual addr 0    H\8c?L "  F 0x0804a010 0    H8c? "  F 0x0804a3b0 0  H  0޽h ? GGGy___PPT10Y+D=' = @B +   0  <(   ~  s *䭳,`0   ~  s *,@0  H  0޽h ? GGGz ! 0  1(   ~  s *Dʳ,`0     <˳8c? P =elibc.so functions called by m.c and a.c are loaded, linked, and (potentially) shared among processes.~f0 ?6?  <ճ8c?0 P  6Shared library of dynamically relocatable object files670 6 B   `wawa?o?   f۳wawa?o?] ]Translators (cc1, as),0   H(8c?* Wm.c0   H8c?)* Wm.o0    fwawa?o?Z ] \Translators (cc1,as),0   Hdz8c?J  Wa.c0   HH8c?)J  Wa.o0 B   `wawa?o? B   `wawa?o?iYB   `wawa?o?i YB   `wawa?o?B   `wawa?o?   H8c?T ;  [libc.so0 B  @  `wawa?o?P P p    fDwawa?o?J  G Linker (ld) 0    H8c? ` p  ;p0    f|wawa?o? p =  #Loader/Dynamic Linker (ld-linux.so) $0 $B   `wawa?o? B  @  `wawa?o? p B  @  `wawa?o?= <  # lhwawa 1))?"k NFully linked executable p (in memory)((00 A2(  # lwawa 1))?" PJ  m)Partially linked executable p (on disk)(*00 A2*  H8c?  >P 0 H  0޽h ? GGGy___PPT10Y+D=' = @B + " 0 =5 (   ~  s *,`0   B   `wawa?o?z   f!wawa?o?sVj R Translator, 0    H'8c?D Wm.c0   H+8c?*D Wm.o0    f@0wawa?o?sv j R Translator, 0    H 48c?d  Wa.c0   H98c?*d  Wa.o0 B   `wawa?o?& & zB   `wawa?o?jZB   `wawa?o?j& & ZB   `wawa?o?B   `wawa?o?& &   H=8c? l  [libc.so0 B  @  `wawa?o?    fBwawa?o? f  NStatic Linker (ld) 0   HF8c?  ;p0    fJwawa?o?    #Loader/Dynamic Linker (ld-linux.so) $0 $B   `wawa?o?*    B   `wawa?o?     HDO8c?1  a libwhatever.a0  B  @  `wawa?o? B   `wawa?o?   s  HU8c?  >p 0   HdY8c? `  [libm.so0 B  @  `wawa?o? @ H  0޽h ? GGGy___PPT10Y+D=' = @B + a 0  (   X  C d     S (d9 3    H  0ηo~ ? 3380___PPT10. V5 b 0  (   X  C d     S ;d9 3    H  0ηo~ ? 3380___PPT10. 0W5 c 0  (   X  C d     S gd9 3    H  0ηo~ ? 3380___PPT10. 0W5 d 0   (   X  C d     S ̤d9 3    H  0ηo~ ? 3380___PPT10. 0W5 e 0 0 (   X  C d     S ũd9 3    H  0ηo~ ? 3380___PPT10. 0W5 f 0 @ (   X  C d     S שd9 3    H  0ηo~ ? 3380___PPT10. *Y5 g 0 P (   X  C d     S  d9 3    H  0ηo~ ? 3380___PPT10. pZ5 h 0 ` (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10. pZ5 i 0 p (   X  C d     S 4NId9 3    H  0ηo~ ? 3380___PPT10. 8\5 j 0  (   X  C d   I  S LId9 3  I  H  0ηo~ ? 3380___PPT10. 8\5 k 0  (   X  C d   I  S Id9 3  I  H  0ηo~ ? 3380___PPT10. 8\5 l 0  (   X  C d     S &d9 3    H  0ηo~ ? 3380___PPT10. ]5 m 0  (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10. ]5 n 0  (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10. PE_5 o 0  (   X  C d     S %d9 3    H  0ηo~ ? 3380___PPT10. PE_5 p 0  (   X  C d     S Jd9 3    H  0ηo~ ? 3380___PPT10. PE_5 q 0  (   X  C d     S wd9 3    H  0ηo~ ? 3380___PPT10. PE_5 r 0  (   X  C d     S hd9 3    H  0ηo~ ? 3380___PPT10. PE_5 s 0  (   X  C d     S $ծd9 3    H  0ηo~ ? 3380___PPT10. `5 t 0   (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10. yb5 u 0 0 (   X  C d     S 4Ld9 3    H  0ηo~ ? 3380___PPT10. @d5 v 0 @ (   X  C d     S PRd9 3    H  0ηo~ ? 3380___PPT10. @d5 w 0 P (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10. e5 x 0 ` (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10. e5 y 0 p (   X  C d     S  d9 3    H  0ηo~ ? 3380___PPT10. e5 z 0  (   X  C d     S @d9 3    H  0ηo~ ? 3380___PPT10.  g5 { 0  (   X  C d     S 䱳d9 3    H  0ηo~ ? 3380___PPT10.  g5 | 0  (   X  C d     S dzd9 3    H  0ηo~ ? 3380___PPT10.  h5 } 0  (   X  C d     S d9 3    H  0ηo~ ? 3380___PPT10.  h5 ~ 0  (   X  C d     S  dd9 3    H  0ηo~ ? 3380___PPT10.  h5r QWd@mpt=yu|ˆ$p3%S, b+)2:WCNPrubaiuy-AUi} 1 E Ym !!#5%I'])aq+x1Oh+'0T hp    (0 CS 343 OSFabian E. Bustamante aqualab01Fabian E. Bustamante98Microsoft PowerPoint@v> @QZ@wIrGSg  )'    """)))UUUMMMBBB999|PP3f333f3333f3ffffff3f̙3ff333f333333333f33333333f33f3ff3f3f3f3333f33̙33333f333333f3333f3ffffff3f33ff3f3f3f3fff3ffffffffff3ffff̙fff3fffff3fff333f3f3ff3ff33f̙̙3̙ff̙̙̙3f̙3f333f3333f3ffffff3f̙3f3f3f333f3333f3ffffff3f̙3f3ffffffffff!___wwwThin4'A x(xKʦ """)))UUUMMMBBB999|PP3f3333f333ff3fffff3f3f̙f3333f3333333333f3333333f3f33ff3f3f3f3333f3333333f3̙33333f333ff3ffffff3f33f3ff3f3f3ffff3fffffffff3fffffff3f̙ffff3ff333f3ff33fff33f3ff̙3f3f3333f333ff3fffff̙̙3̙f̙̙̙3f̙3f3f3333f333ff3fffff3f3f̙3ffffffffff!___wwweeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮϮ՜.+,0  $ , BOn-screen Show$CompSci - Northwestern UniversityY 'ArialTahomaTimes New Roman WingdingsVerdana Courier NewTimes Helvetica 1_aqualab01LinkingLinker puzzles(A simplistic program translation schemeA better scheme using a linker!Translating the example program What does a linker do? 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Bustamante  !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~      !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcefghijklmnopqrstuvwxyz{|}~Root EntrydO)Pictures2Current UserSummaryInformation(dUPowerPoint Document(M,DocumentSummaryInformation8