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On 2019/7/23 9:21 PM, Florian Weimer wrote:
Is => intended to cover the case of run-time dependencies added late due to lazy binding? Currently, those late dependencies have two effects, I think: They keep around the referenced libraries longer than before (so that dlclose would not remove an object which is still in used solely due to lazy binding). And the ELF destructors are reordered to reflect these added run-time dependencies.
Yes, you can test that. The effect of => is to create a caller/callee relation between objects: 'x=>y' creates fn_x() and fn_y() in those two DSOs, and fn_x() has a call to fn_y(). Though that's the only immediate effect that => has. To construct a test of run-time added dependencies related to dlopen/etc. you also need to add those operations inside the '{}' construct. All the created DSOs have a constructor/destructor that outputs their single character name. The generated main() program prints '[]' brackets after dlopen/dlclose calls to separate out the following constructor/destructor output. So taken whole, the entire output string should capture all constructor/destructor activity and ordering behavior.
Can your test framework test both cases? What's your position on the second effect? I think it sometimes results in destructors running not in the opposite order of constructors, due to the new topological sort. (This also happens with the current implementation.)
What I did in the ld.so code patch was add a second pass of sorting that ignores runtime deps, prioritizing link dependencies; this appears to also be what prior discussion pointed towards, see more details in that 2nd email with the actual code patch. I have attached an updated patch here; fixed some bugs in the script related to the '@' operator for the main program construct. Thanks, Chung-Lin
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dlsort-01-tests-v2.patch
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