| 1 | #include "library_file.h" |
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| 2 | #include <link.h> |
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| 3 | #include <stdio.h> |
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| 4 | // Make a duplicate "_r_debug" symbol that is visible. This is the global |
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| 5 | // variable name that the dynamic loader uses to communicate changes in shared |
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| 6 | // libraries that get loaded and unloaded. LLDB finds the address of this |
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| 7 | // variable by reading the DT_DEBUG entry from the .dynamic section of the main |
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| 8 | // executable. |
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| 9 | // What will happen is the dynamic loader will use the "_r_debug" symbol from |
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| 10 | // itself until the a.out executable gets loaded. At this point the new |
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| 11 | // "_r_debug" symbol will take precedence over the orignal "_r_debug" symbol |
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| 12 | // from the dynamic loader and the copy below will get updated with shared |
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| 13 | // library state changes while the version that LLDB checks in the dynamic |
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| 14 | // loader stays the same for ever after this. |
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| 15 | // |
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| 16 | // When our DYLDRendezvous.cpp tries to check the state in the _r_debug |
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| 17 | // structure, it will continue to get the last eAdd as the state before the |
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| 18 | // switch in symbol resolution. |
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| 19 | // |
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| 20 | // Before a fix in LLDB, this would mean that we wouldn't ever load any shared |
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| 21 | // libraries since DYLDRendezvous was waiting to see a eAdd state followed by a |
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| 22 | // eConsistent state which would trigger the adding of shared libraries, but we |
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| 23 | // would never see this change because the local copy below is actually what |
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| 24 | // would get updated. Now if DYLDRendezvous detects two eAdd states in a row, |
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| 25 | // it will load the shared libraries instead of doing nothing and a log message |
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| 26 | // will be printed out if "log enable lldb dyld" is active. |
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| 27 | r_debug _r_debug; |
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| 28 | |
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| 29 | int main() { |
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| 30 | library_function(); // Break here |
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| 31 | return 0; |
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| 32 | } |
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| 33 | |
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