236 lines
8.8 KiB
Diff
236 lines
8.8 KiB
Diff
commit d0f07f7df8d9758c838674b70144ac73bcbd1634
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Tue May 30 13:25:50 2023 +0200
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elf: Make more functions available for binding during dlclose (bug 30425)
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Previously, after destructors for a DSO have been invoked, ld.so refused
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to bind against that DSO in all cases. Relax this restriction somewhat
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if the referencing object is itself a DSO that is being unloaded. This
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assumes that the symbol reference is not going to be stored anywhere.
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The situation in the test case can arise fairly easily with C++ and
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objects that are built with different optimization levels and therefore
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define different functions with vague linkage.
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Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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Conflicts:
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elf/Makefile
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(usual test differences, link test with -ldl)
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diff --git a/elf/Makefile b/elf/Makefile
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index 634c3113227d64a6..42dc878209b11d29 100644
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--- a/elf/Makefile
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+++ b/elf/Makefile
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@@ -362,6 +362,7 @@ tests += \
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tst-big-note \
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tst-debug1 \
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tst-deep1 \
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+ tst-dlclose-lazy \
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tst-dlmodcount \
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tst-dlmopen1 \
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tst-dlmopen3 \
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@@ -709,6 +710,8 @@ modules-names = \
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tst-deep1mod2 \
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tst-deep1mod3 \
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tst-dlmopen1mod \
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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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@@ -2697,3 +2700,10 @@ $(objpfx)tst-dlmopen-twice: $(libdl)
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$(objpfx)tst-dlmopen-twice.out: \
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$(objpfx)tst-dlmopen-twice-mod1.so \
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$(objpfx)tst-dlmopen-twice-mod2.so
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+
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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: $(libdl)
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+$(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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+
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diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c
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index 47acd134600b44b5..9e8f14b8483f5eba 100644
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--- a/elf/dl-lookup.c
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+++ b/elf/dl-lookup.c
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@@ -380,8 +380,25 @@ do_lookup_x (const char *undef_name, uint_fast32_t 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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+
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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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+
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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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diff --git a/elf/tst-dlclose-lazy-mod1.c b/elf/tst-dlclose-lazy-mod1.c
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new file mode 100644
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index 0000000000000000..8439dc1925cc8b41
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--- /dev/null
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+++ b/elf/tst-dlclose-lazy-mod1.c
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@@ -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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+
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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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+
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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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+
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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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+
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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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+
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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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diff --git a/elf/tst-dlclose-lazy-mod2.c b/elf/tst-dlclose-lazy-mod2.c
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new file mode 100644
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index 0000000000000000..767f69ffdb23a685
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--- /dev/null
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+++ b/elf/tst-dlclose-lazy-mod2.c
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@@ -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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+
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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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+
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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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+
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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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+
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+#include <stdio.h>
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+#include <stdlib.h>
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+
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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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+
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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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+
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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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+
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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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+
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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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diff --git a/elf/tst-dlclose-lazy.c b/elf/tst-dlclose-lazy.c
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new file mode 100644
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index 0000000000000000..976a6bb6f64fa981
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--- /dev/null
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+++ b/elf/tst-dlclose-lazy.c
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@@ -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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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+ return 0;
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+}
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