32 lines
1.6 KiB
C++
32 lines
1.6 KiB
C++
#include "library_file.h"
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#include <link.h>
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#include <stdio.h>
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// Make a duplicate "_r_debug" symbol that is visible. This is the global
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// variable name that the dynamic loader uses to communicate changes in shared
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// libraries that get loaded and unloaded. LLDB finds the address of this
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// variable by reading the DT_DEBUG entry from the .dynamic section of the main
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// executable.
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// What will happen is the dynamic loader will use the "_r_debug" symbol from
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// itself until the a.out executable gets loaded. At this point the new
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// "_r_debug" symbol will take precedence over the orignal "_r_debug" symbol
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// from the dynamic loader and the copy below will get updated with shared
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// library state changes while the version that LLDB checks in the dynamic
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// loader stays the same for ever after this.
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//
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// When our DYLDRendezvous.cpp tries to check the state in the _r_debug
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// structure, it will continue to get the last eAdd as the state before the
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// switch in symbol resolution.
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//
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// Before a fix in LLDB, this would mean that we wouldn't ever load any shared
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// libraries since DYLDRendezvous was waiting to see a eAdd state followed by a
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// eConsistent state which would trigger the adding of shared libraries, but we
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// would never see this change because the local copy below is actually what
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// would get updated. Now if DYLDRendezvous detects two eAdd states in a row,
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// it will load the shared libraries instead of doing nothing and a log message
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// will be printed out if "log enable lldb dyld" is active.
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r_debug _r_debug;
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int main() {
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library_function(); // Break here
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return 0;
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}
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