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1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
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2 @c This is part of the GCC manual.
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3 @c For copying conditions, see the file gcc.texi.
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4
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5 @node Collect2
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6 @chapter @code{collect2}
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7
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8 GCC uses a utility called @code{collect2} on nearly all systems to arrange
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9 to call various initialization functions at start time.
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10
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11 The program @code{collect2} works by linking the program once and
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12 looking through the linker output file for symbols with particular names
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13 indicating they are constructor functions. If it finds any, it
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14 creates a new temporary @samp{.c} file containing a table of them,
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15 compiles it, and links the program a second time including that file.
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16
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17 @findex __main
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18 @cindex constructors, automatic calls
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19 The actual calls to the constructors are carried out by a subroutine
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20 called @code{__main}, which is called (automatically) at the beginning
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21 of the body of @code{main} (provided @code{main} was compiled with GNU
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22 CC)@. Calling @code{__main} is necessary, even when compiling C code, to
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23 allow linking C and C++ object code together. (If you use
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24 @option{-nostdlib}, you get an unresolved reference to @code{__main},
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25 since it's defined in the standard GCC library. Include @option{-lgcc} at
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26 the end of your compiler command line to resolve this reference.)
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27
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28 The program @code{collect2} is installed as @code{ld} in the directory
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29 where the passes of the compiler are installed. When @code{collect2}
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30 needs to find the @emph{real} @code{ld}, it tries the following file
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31 names:
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32
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33 @itemize @bullet
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34 @item
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35 @file{real-ld} in the directories listed in the compiler's search
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36 directories.
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37
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38 @item
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39 @file{real-ld} in the directories listed in the environment variable
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40 @code{PATH}.
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41
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42 @item
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43 The file specified in the @code{REAL_LD_FILE_NAME} configuration macro,
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44 if specified.
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45
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46 @item
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47 @file{ld} in the compiler's search directories, except that
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48 @code{collect2} will not execute itself recursively.
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49
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50 @item
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51 @file{ld} in @code{PATH}.
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52 @end itemize
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53
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54 ``The compiler's search directories'' means all the directories where
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55 @command{gcc} searches for passes of the compiler. This includes
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56 directories that you specify with @option{-B}.
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57
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58 Cross-compilers search a little differently:
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59
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60 @itemize @bullet
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61 @item
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62 @file{real-ld} in the compiler's search directories.
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63
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64 @item
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65 @file{@var{target}-real-ld} in @code{PATH}.
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66
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67 @item
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68 The file specified in the @code{REAL_LD_FILE_NAME} configuration macro,
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69 if specified.
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70
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71 @item
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72 @file{ld} in the compiler's search directories.
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73
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74 @item
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75 @file{@var{target}-ld} in @code{PATH}.
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76 @end itemize
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77
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78 @code{collect2} explicitly avoids running @code{ld} using the file name
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79 under which @code{collect2} itself was invoked. In fact, it remembers
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80 up a list of such names---in case one copy of @code{collect2} finds
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81 another copy (or version) of @code{collect2} installed as @code{ld} in a
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82 second place in the search path.
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83
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84 @code{collect2} searches for the utilities @code{nm} and @code{strip}
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85 using the same algorithm as above for @code{ld}.
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