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90 lines
4.3 KiB
90 lines
4.3 KiB
commit 1df71d32fe5f5905ffd5d100e5e9ca8ad6210891 |
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Author: Florian Weimer <fweimer@redhat.com> |
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Date: Tue Sep 20 11:00:42 2022 +0200 |
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elf: Implement force_first handling in _dl_sort_maps_dfs (bug 28937) |
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The implementation in _dl_close_worker requires that the first |
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element of l_initfini is always this very map (“We are always the |
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zeroth entry, and since we don't include ourselves in the |
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dependency analysis start at 1.”). Rather than fixing that |
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assumption, this commit adds an implementation of the force_first |
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argument to the new dependency sorting algorithm. This also means |
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that the directly dlopen'ed shared object is always initialized last, |
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which is the least surprising behavior in the presence of cycles. |
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Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> |
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diff --git a/elf/dl-sort-maps.c b/elf/dl-sort-maps.c |
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index 7c614bca5d8115c6..e8ef5e8b3588ab53 100644 |
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--- a/elf/dl-sort-maps.c |
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+++ b/elf/dl-sort-maps.c |
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@@ -182,8 +182,9 @@ dfs_traversal (struct link_map ***rpo, struct link_map *map, |
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static void |
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_dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps, |
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- bool force_first __attribute__ ((unused)), bool for_fini) |
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+ bool force_first, bool for_fini) |
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{ |
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+ struct link_map *first_map = maps[0]; |
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for (int i = nmaps - 1; i >= 0; i--) |
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maps[i]->l_visited = 0; |
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@@ -208,14 +209,6 @@ _dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps, |
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Adjusting the order so that maps[0] is last traversed naturally avoids |
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this problem. |
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- Further, the old "optimization" of skipping the main object at maps[0] |
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- from the call-site (i.e. _dl_sort_maps(maps+1,nmaps-1)) is in general |
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- no longer valid, since traversing along object dependency-links |
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- may "find" the main object even when it is not included in the initial |
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- order (e.g. a dlopen()'ed shared object can have circular dependencies |
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- linked back to itself). In such a case, traversing N-1 objects will |
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- create a N-object result, and raise problems. |
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- |
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To summarize, just passing in the full list, and iterating from back |
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to front makes things much more straightforward. */ |
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@@ -274,6 +267,27 @@ _dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps, |
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} |
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memcpy (maps, rpo, sizeof (struct link_map *) * nmaps); |
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+ |
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+ /* Skipping the first object at maps[0] is not valid in general, |
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+ since traversing along object dependency-links may "find" that |
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+ first object even when it is not included in the initial order |
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+ (e.g., a dlopen'ed shared object can have circular dependencies |
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+ linked back to itself). In such a case, traversing N-1 objects |
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+ will create a N-object result, and raise problems. Instead, |
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+ force the object back into first place after sorting. This naive |
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+ approach may introduce further dependency ordering violations |
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+ compared to rotating the cycle until the first map is again in |
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+ the first position, but as there is a cycle, at least one |
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+ violation is already present. */ |
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+ if (force_first && maps[0] != first_map) |
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+ { |
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+ int i; |
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+ for (i = 0; maps[i] != first_map; ++i) |
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+ ; |
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+ assert (i < nmaps); |
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+ memmove (&maps[1], maps, i * sizeof (maps[0])); |
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+ maps[0] = first_map; |
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+ } |
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} |
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void |
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diff --git a/elf/dso-sort-tests-1.def b/elf/dso-sort-tests-1.def |
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index 5f7f18ef270bc12d..4bf9052db16fb352 100644 |
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--- a/elf/dso-sort-tests-1.def |
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+++ b/elf/dso-sort-tests-1.def |
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@@ -64,3 +64,10 @@ output: b>a>{}<a<b |
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tst-bz15311: {+a;+e;+f;+g;+d;%d;-d;-g;-f;-e;-a};a->b->c->d;d=>[ba];c=>a;b=>e=>a;c=>f=>b;d=>g=>c |
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output(glibc.rtld.dynamic_sort=1): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<a<c<d<g<f<b<e];} |
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output(glibc.rtld.dynamic_sort=2): {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[<g<f<a<b<c<d<e];} |
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+ |
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+# Test that even in the presence of dependency loops involving dlopen'ed |
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+# object, that object is initialized last (and not unloaded prematurely). |
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+# Final destructor order is indeterminate due to the cycle. |
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+tst-bz28937: {+a;+b;-b;+c;%c};a->a1;a->a2;a2->a;b->b1;c->a1;c=>a1 |
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+output(glibc.rtld.dynamic_sort=1): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a<a2<c<a1 |
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+output(glibc.rtld.dynamic_sort=2): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a2<a<c<a1
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