mirror of git://sourceware.org/git/glibc.git
d7f587398c
The current DSO dependency sorting tests are for a limited number of specific cases, including some from particular bug reports. Add tests that systematically cover all possible DAGs for an executable and the shared libraries it depends on, directly or indirectly, up to four objects (an executable and three shared libraries). (For this kind of DAG - ones with a single source vertex from which all others are reachable, and an ordering on the edges from each vertex - there are 57 DAGs on four vertices, 3399 on five vertices and 1026944 on six vertices; see https://arxiv.org/pdf/2303.14710 for more details on this enumeration. I've tested that the 3399 cases with five vertices do all pass if enabled.) These tests are replicating the sorting logic from the dynamic linker (thereby, for example, asserting that it doesn't accidentally change); I'm not claiming that the logic in the dynamic linker is in some abstract sense optimal. Note that these tests do illustrate how in some cases the two sorting algorithms produce different results for a DAG (I think all the existing tests for such differences are ones involving cycles, and the motivation for the new algorithm was also to improve the handling of cycles): tst-dso-ordering-all4-44: a->[bc];{}->[cba] output(glibc.rtld.dynamic_sort=1): c>b>a>{}<a<b<c output(glibc.rtld.dynamic_sort=2): b>c>a>{}<a<c<b They also illustrate that sometimes the sorting algorithms do not follow the order in which dependencies are listed in DT_NEEDED even though there is a valid topological sort that does follow that, which might be counterintuitive considering that the DT_NEEDED ordering is followed in the simplest cases: tst-dso-ordering-all4-56: {}->[abc] output: c>b>a>{}<a<b<c shows such a simple case following DT_NEEDED order for destructor execution (the reverse of it for constructor execution), but tst-dso-ordering-all4-41: a->[cb];{}->[cba] output: c>b>a>{}<a<b<c shows that c and b are in the opposite order to what might be expected from the simplest case, though there is no dependency requiring such an opposite order to be used. (I'm not asserting that either of those things is a problem, simply observing them as less obvious properties of the sorting algorithms shown up by these tests.) Tested for x86_64. |
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