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1 DYNODUMP
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2 --------
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3
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4 Dynodump, not to be confused with DinoTurd (as seen in Jurassic Park),
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5 is a shared object that provides one function:
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6
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7 int dynodump(char *new_file);
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8
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9 dynodump(), called from a running program will write a new executable
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10 in new_file a la unexec() in GNU Emacs. The difference lies in the
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11 relocations.
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12
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13 dynodump() will create an image with any relocations (which were
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14 performed by the run-time dynamic linker) undone. This allows the new
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15 image to be run in a different environment. There is, however, one
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16 potentially major caveat. If a symbol reference gets updated during
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17 the running of the calling program, its updated value will be lost.
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18 An example (with additional blank lines for legibility):
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19
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20 $ cat lib.c
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21 char _foo[] = "hello";
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22 char _bar[] = "world";
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23
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24 $ cc -G -o lib.so lib.c
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25
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26 $ cat prog.c
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27 extern char _foo, _bar;
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28
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29 int beenhere = 0;
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30 char * foo = &_foo;
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31 char * bar = &_bar;
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32
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33 int
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34 main(void)
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35 {
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36 (void) printf("%d: foo = %x\n", beenhere, foo);
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37 (void) printf("%d: bar = %x, ", beenhere, bar);
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38
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39 if (!beenhere) {
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40 beenhere = 1;
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41 bar++;
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42 dynodump("newfile");
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43 }
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44 (void) printf("%x\n", bar);
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45 }
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46
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47 $ cc -o prog prog.c -R. lib.so dynodump.so
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48
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49 $ ./prog
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50 0: foo = ef7503cc
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51 0: bar = ef7503d2, ef7503d3
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52
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53 $ ./newfile
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54 1: foo = ef7503cc
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55 1: bar = ef7503d2, ef7503d2
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56
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57 Notice that in the run of newfile, bar points at "world" instead of
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58 the perhaps expected "orld".
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59
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60 Dynodump supports sparc, intel, and power pc architectures.
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61
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62 Dynodump is buildable with GNU make and gcc. If it works for you
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63 with these tools, let me know.
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64
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65 unexec()
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66 --------
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67
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68 Also supplied is an unexsol2.c which belongs in the XEmacs src
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69 directory with the other unex*.c files. The src/s/sol2.h should be
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70 have the following added to it:
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71
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72 #ifdef UNEXEC
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73 #undef UNEXEC
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74 #endif
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75 #define UNEXEC unexsol2.o
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76
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77 This unexec() will attempt to dlopen() the dynodump.so to find the
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78 dynodump function. The default is "../dynodump/dynodump.so" which
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79 should be appropriate for the typical XEmacs build (unless you used
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80 configure to set up separate build and source trees). You may change
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81 it by setting the DYNODUMP environment variable to the full path of
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82 the dynodump shared object.
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83
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84 Other notes:
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85
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86 If you're using the 4.0 C compiler from Sun, you should arrange to
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87 shut off the incremental linker. This is done with the -xildoff
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88 option to the compiler. The common.mk and testsuite/Makefile files
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89 have commentary and ready made lines for uncommenting for this
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90 purpose.
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91
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92 If you're interested in playing with the UltraSPARC specific options
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93 to the aforementioned compiler, then the same makefiles have some
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94 commentary and flags settings to point you in that direction.
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95
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96 Questions:
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97
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98 dynodump() was developed by Rod.Evans@Eng.Sun.COM and
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99 Georg.Nikodym@Canada.Sun.COM. If you have questions, feel free to ask
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100 them but be aware that Rod, "don't know jack about emacs."
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101
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