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elf: Make more functions available for binding during dlclose (bug 30425)
Previously, after destructors for a DSO have been invoked, ld.so refused to bind against that DSO in all cases. Relax this restriction somewhat if the referencing object is itself a DSO that is being unloaded. This assumes that the symbol reference is not going to be stored anywhere. The situation in the test case can arise fairly easily with C++ and objects that are built with different optimization levels and therefore define different functions with vague linkage. Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Florian Weimer
parent
3eed5f3a1e
commit
d0f07f7df8
@ -396,6 +396,7 @@ tests += \
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tst-debug1 \
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tst-deep1 \
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tst-dl-is_dso \
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tst-dlclose-lazy \
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tst-dlmodcount \
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tst-dlmopen-dlerror \
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tst-dlmopen-gethostbyname \
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@ -816,6 +817,8 @@ modules-names += \
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tst-dl_find_object-mod7 \
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tst-dl_find_object-mod8 \
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tst-dl_find_object-mod9 \
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tst-dlclose-lazy-mod1 \
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tst-dlclose-lazy-mod2 \
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tst-dlmopen-dlerror-mod \
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tst-dlmopen-gethostbyname-mod \
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tst-dlmopen-twice-mod1 \
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@ -3001,3 +3004,8 @@ $(objpfx)tst-sprof-basic.out: tst-sprof-basic.sh $(objpfx)tst-sprof-basic
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'$(run-program-env)' > $@; \
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$(evaluate-test)
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generated += tst-sprof-mod.so.profile
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LDFLAGS-tst-dlclose-lazy-mod1.so = -Wl,-z,lazy,--no-as-needed
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$(objpfx)tst-dlclose-lazy-mod1.so: $(objpfx)tst-dlclose-lazy-mod2.so
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$(objpfx)tst-dlclose-lazy.out: \
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$(objpfx)tst-dlclose-lazy-mod1.so $(objpfx)tst-dlclose-lazy-mod2.so
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@ -366,8 +366,25 @@ do_lookup_x (const char *undef_name, unsigned int new_hash,
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if ((type_class & ELF_RTYPE_CLASS_COPY) && map->l_type == lt_executable)
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continue;
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/* Do not look into objects which are going to be removed. */
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if (map->l_removed)
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/* Do not look into objects which are going to be removed,
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except when the referencing object itself is being removed.
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The second part covers the situation when an object lazily
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binds to another object while running its destructor, but the
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destructor of the other object has already run, so that
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dlclose has set l_removed. It may not always be obvious how
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to avoid such a scenario to programmers creating DSOs,
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particularly if C++ vague linkage is involved and triggers
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symbol interposition.
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Accepting these to-be-removed objects makes the lazy and
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BIND_NOW cases more similar. (With BIND_NOW, the symbol is
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resolved early, before the destructor call, so the issue does
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not arise.). Behavior matches the constructor scenario: the
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implementation allows binding to symbols of objects whose
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constructors have not run. In fact, not doing this would be
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mostly incompatible with symbol interposition. */
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if (map->l_removed && !(undef_map != NULL && undef_map->l_removed))
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continue;
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/* Print some debugging info if wanted. */
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36
elf/tst-dlclose-lazy-mod1.c
Normal file
36
elf/tst-dlclose-lazy-mod1.c
Normal file
@ -0,0 +1,36 @@
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/* Lazy binding during dlclose. Directly loaded module.
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Copyright (C) 2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* This function is called from exported_function below. It is only
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defined in this module. The weak attribute mimics how G++
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implements vague linkage for C++. */
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void __attribute__ ((weak))
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lazily_bound_exported_function (void)
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{
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}
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/* Called from tst-dlclose-lazy-mod2.so. */
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void
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exported_function (int call_it)
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{
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if (call_it)
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/* Previous to the fix this would crash when called during dlclose
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since symbols from the DSO were no longer available for binding
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(bug 30425) after the DSO started being closed by dlclose. */
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lazily_bound_exported_function ();
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}
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49
elf/tst-dlclose-lazy-mod2.c
Normal file
49
elf/tst-dlclose-lazy-mod2.c
Normal file
@ -0,0 +1,49 @@
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/* Lazy binding during dlclose. Indirectly loaded module.
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Copyright (C) 2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <stdio.h>
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#include <stdlib.h>
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void
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exported_function (int ignored)
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{
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/* This function is interposed from tst-dlclose-lazy-mod1.so and
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thus never called. */
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abort ();
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}
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static void __attribute__ ((constructor))
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init (void)
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{
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puts ("info: tst-dlclose-lazy-mod2.so constructor called");
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/* Trigger lazy binding to the definition in
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tst-dlclose-lazy-mod1.so, but not for
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lazily_bound_exported_function in that module. */
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exported_function (0);
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}
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static void __attribute__ ((destructor))
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fini (void)
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{
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puts ("info: tst-dlclose-lazy-mod2.so destructor called");
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/* Trigger the lazily_bound_exported_function call in
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exported_function in tst-dlclose-lazy-mod1.so. */
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exported_function (1);
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}
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47
elf/tst-dlclose-lazy.c
Normal file
47
elf/tst-dlclose-lazy.c
Normal file
@ -0,0 +1,47 @@
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/* Test lazy binding during dlclose (bug 30425).
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Copyright (C) 2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* This test re-creates a situation that can arise naturally for C++
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applications due to the use of vague linkage and differences in the
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set of compiler-emitted functions. A function in
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tst-dlclose-lazy-mod1.so (exported_function) interposes a function
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in tst-dlclose-lazy-mod2.so. This function is called from the
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destructor in tst-dlclose-lazy-mod2.so, after the destructor for
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tst-dlclose-lazy-mod1.so has already completed. Prior to the fix
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for bug 30425, this would lead to a lazy binding failure in
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tst-dlclose-lazy-mod1.so because dlclose had already marked the DSO
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as unavailable for binding (by setting l_removed). */
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#include <dlfcn.h>
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#include <support/xdlfcn.h>
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#include <support/check.h>
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int
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main (void)
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{
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/* Load tst-dlclose-lazy-mod1.so, indirectly loading
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tst-dlclose-lazy-mod2.so. */
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void *handle = xdlopen ("tst-dlclose-lazy-mod1.so", RTLD_GLOBAL | RTLD_LAZY);
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/* Invoke the destructor of tst-dlclose-lazy-mod2.so, which calls
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into tst-dlclose-lazy-mod1.so after its destructor has been
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called. */
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xdlclose (handle);
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return 0;
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}
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