91 lines
4.3 KiB
Diff
91 lines
4.3 KiB
Diff
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 7a586749adc3fa7d..6f5c17b47b98fbc7 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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