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comparison dynodump/README @ 0:376386a54a3c r19-14

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Import from CVS: tag r19-14
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date Mon, 13 Aug 2007 08:45:50 +0200
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1 DYNODUMP
2 --------
3
4 Dynodump, not to be confused with DinoTurd (as seen in Jurassic Park),
5 is a shared object that provides one function:
6
7 int dynodump(char *new_file);
8
9 dynodump(), called from a running program will write a new executable
10 in new_file a la unexec() in GNU Emacs. The difference lies in the
11 relocations.
12
13 dynodump() will create an image with any relocations (which were
14 performed by the run-time dynamic linker) undone. This allows the new
15 image to be run in a different environment. There is, however, one
16 potentially major caveat. If a symbol reference gets updated during
17 the running of the calling program, its updated value will be lost.
18 An example (with additional blank lines for legibility):
19
20 $ cat lib.c
21 char _foo[] = "hello";
22 char _bar[] = "world";
23
24 $ cc -G -o lib.so lib.c
25
26 $ cat prog.c
27 extern char _foo, _bar;
28
29 int beenhere = 0;
30 char * foo = &_foo;
31 char * bar = &_bar;
32
33 int
34 main(void)
35 {
36 (void) printf("%d: foo = %x\n", beenhere, foo);
37 (void) printf("%d: bar = %x, ", beenhere, bar);
38
39 if (!beenhere) {
40 beenhere = 1;
41 bar++;
42 dynodump("newfile");
43 }
44 (void) printf("%x\n", bar);
45 }
46
47 $ cc -o prog prog.c -R. lib.so dynodump.so
48
49 $ ./prog
50 0: foo = ef7503cc
51 0: bar = ef7503d2, ef7503d3
52
53 $ ./newfile
54 1: foo = ef7503cc
55 1: bar = ef7503d2, ef7503d2
56
57 Notice that in the run of newfile, bar points at "world" instead of
58 the perhaps expected "orld".
59
60 Dynodump supports sparc, intel, and power pc architectures.
61
62 Dynodump is buildable with GNU make and gcc. If it works for you
63 with these tools, let me know.
64
65 unexec()
66 --------
67
68 Also supplied is an unexsol2.c which belongs in the XEmacs src
69 directory with the other unex*.c files. The src/s/sol2.h should be
70 have the following added to it:
71
72 #ifdef UNEXEC
73 #undef UNEXEC
74 #endif
75 #define UNEXEC unexsol2.o
76
77 This unexec() will attempt to dlopen() the dynodump.so to find the
78 dynodump function. The default is "../dynodump/dynodump.so" which
79 should be appropriate for the typical XEmacs build (unless you used
80 configure to set up separate build and source trees). You may change
81 it by setting the DYNODUMP environment variable to the full path of
82 the dynodump shared object.
83
84 Other notes:
85
86 If you're using the 4.0 C compiler from Sun, you should arrange to
87 shut off the incremental linker. This is done with the -xildoff
88 option to the compiler. The common.mk and testsuite/Makefile files
89 have commentary and ready made lines for uncommenting for this
90 purpose.
91
92 If you're interested in playing with the UltraSPARC specific options
93 to the aforementioned compiler, then the same makefiles have some
94 commentary and flags settings to point you in that direction.
95
96 Questions:
97
98 dynodump() was developed by Rod.Evans@Eng.Sun.COM and
99 Georg.Nikodym@Canada.Sun.COM. If you have questions, feel free to ask
100 them but be aware that Rod, "don't know jack about emacs."
101