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commit d0f07f7df8d9758c838674b70144ac73bcbd1634
Author: Florian Weimer <fweimer@redhat.com>
Date: Tue May 30 13:25:50 2023 +0200
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>
Conflicts:
elf/Makefile
(usual test differences, link test with -ldl)
diff --git a/elf/Makefile b/elf/Makefile
index 6f0f36cdfe3961e8..ebf46a297d241d8f 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -362,6 +362,7 @@ tests += \
tst-big-note \
tst-debug1 \
tst-deep1 \
+ tst-dlclose-lazy \
tst-dlmodcount \
tst-dlmopen1 \
tst-dlmopen3 \
@@ -711,6 +712,8 @@ modules-names = \
tst-deep1mod2 \
tst-deep1mod3 \
tst-dlmopen1mod \
+ tst-dlclose-lazy-mod1 \
+ tst-dlclose-lazy-mod2 \
tst-dlmopen-dlerror-mod \
tst-dlmopen-gethostbyname-mod \
tst-dlmopen-twice-mod1 \
@@ -2707,6 +2710,12 @@ $(objpfx)tst-dlmopen-twice.out: \
$(objpfx)tst-dlmopen-twice-mod1.so \
$(objpfx)tst-dlmopen-twice-mod2.so
+LDFLAGS-tst-dlclose-lazy-mod1.so = -Wl,-z,lazy,--no-as-needed
+$(objpfx)tst-dlclose-lazy-mod1.so: $(objpfx)tst-dlclose-lazy-mod2.so
+$(objpfx)tst-dlclose-lazy: $(libdl)
+$(objpfx)tst-dlclose-lazy.out: \
+ $(objpfx)tst-dlclose-lazy-mod1.so $(objpfx)tst-dlclose-lazy-mod2.so
+
# The object tst-nodeps1-mod.so has no explicit dependencies on libc.so.
$(objpfx)tst-nodeps1-mod.so: $(objpfx)tst-nodeps1-mod.os
$(LINK.o) -nostartfiles -nostdlib -shared -o $@ $^
diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c
index 47acd134600b44b5..9e8f14b8483f5eba 100644
--- a/elf/dl-lookup.c
+++ b/elf/dl-lookup.c
@@ -380,8 +380,25 @@ do_lookup_x (const char *undef_name, uint_fast32_t new_hash,
if ((type_class & ELF_RTYPE_CLASS_COPY) && map->l_type == lt_executable)
continue;
- /* Do not look into objects which are going to be removed. */
- if (map->l_removed)
+ /* Do not look into objects which are going to be removed,
+ except when the referencing object itself is being removed.
+
+ The second part covers the situation when an object lazily
+ binds to another object while running its destructor, but the
+ destructor of the other object has already run, so that
+ dlclose has set l_removed. It may not always be obvious how
+ to avoid such a scenario to programmers creating DSOs,
+ particularly if C++ vague linkage is involved and triggers
+ symbol interposition.
+
+ Accepting these to-be-removed objects makes the lazy and
+ BIND_NOW cases more similar. (With BIND_NOW, the symbol is
+ resolved early, before the destructor call, so the issue does
+ not arise.). Behavior matches the constructor scenario: the
+ implementation allows binding to symbols of objects whose
+ constructors have not run. In fact, not doing this would be
+ mostly incompatible with symbol interposition. */
+ if (map->l_removed && !(undef_map != NULL && undef_map->l_removed))
continue;
/* Print some debugging info if wanted. */
diff --git a/elf/tst-dlclose-lazy-mod1.c b/elf/tst-dlclose-lazy-mod1.c
new file mode 100644
index 0000000000000000..8439dc1925cc8b41
--- /dev/null
+++ b/elf/tst-dlclose-lazy-mod1.c
@@ -0,0 +1,36 @@
+/* Lazy binding during dlclose. Directly loaded module.
+ Copyright (C) 2023 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+/* This function is called from exported_function below. It is only
+ defined in this module. The weak attribute mimics how G++
+ implements vague linkage for C++. */
+void __attribute__ ((weak))
+lazily_bound_exported_function (void)
+{
+}
+
+/* Called from tst-dlclose-lazy-mod2.so. */
+void
+exported_function (int call_it)
+{
+ if (call_it)
+ /* Previous to the fix this would crash when called during dlclose
+ since symbols from the DSO were no longer available for binding
+ (bug 30425) after the DSO started being closed by dlclose. */
+ lazily_bound_exported_function ();
+}
diff --git a/elf/tst-dlclose-lazy-mod2.c b/elf/tst-dlclose-lazy-mod2.c
new file mode 100644
index 0000000000000000..767f69ffdb23a685
--- /dev/null
+++ b/elf/tst-dlclose-lazy-mod2.c
@@ -0,0 +1,49 @@
+/* Lazy binding during dlclose. Indirectly loaded module.
+ Copyright (C) 2023 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+void
+exported_function (int ignored)
+{
+ /* This function is interposed from tst-dlclose-lazy-mod1.so and
+ thus never called. */
+ abort ();
+}
+
+static void __attribute__ ((constructor))
+init (void)
+{
+ puts ("info: tst-dlclose-lazy-mod2.so constructor called");
+
+ /* Trigger lazy binding to the definition in
+ tst-dlclose-lazy-mod1.so, but not for
+ lazily_bound_exported_function in that module. */
+ exported_function (0);
+}
+
+static void __attribute__ ((destructor))
+fini (void)
+{
+ puts ("info: tst-dlclose-lazy-mod2.so destructor called");
+
+ /* Trigger the lazily_bound_exported_function call in
+ exported_function in tst-dlclose-lazy-mod1.so. */
+ exported_function (1);
+}
diff --git a/elf/tst-dlclose-lazy.c b/elf/tst-dlclose-lazy.c
new file mode 100644
index 0000000000000000..976a6bb6f64fa981
--- /dev/null
+++ b/elf/tst-dlclose-lazy.c
@@ -0,0 +1,47 @@
+/* Test lazy binding during dlclose (bug 30425).
+ Copyright (C) 2023 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+/* This test re-creates a situation that can arise naturally for C++
+ applications due to the use of vague linkage and differences in the
+ set of compiler-emitted functions. A function in
+ tst-dlclose-lazy-mod1.so (exported_function) interposes a function
+ in tst-dlclose-lazy-mod2.so. This function is called from the
+ destructor in tst-dlclose-lazy-mod2.so, after the destructor for
+ tst-dlclose-lazy-mod1.so has already completed. Prior to the fix
+ for bug 30425, this would lead to a lazy binding failure in
+ tst-dlclose-lazy-mod1.so because dlclose had already marked the DSO
+ as unavailable for binding (by setting l_removed). */
+
+#include <dlfcn.h>
+#include <support/xdlfcn.h>
+#include <support/check.h>
+
+int
+main (void)
+{
+ /* Load tst-dlclose-lazy-mod1.so, indirectly loading
+ tst-dlclose-lazy-mod2.so. */
+ void *handle = xdlopen ("tst-dlclose-lazy-mod1.so", RTLD_GLOBAL | RTLD_LAZY);
+
+ /* Invoke the destructor of tst-dlclose-lazy-mod2.so, which calls
+ into tst-dlclose-lazy-mod1.so after its destructor has been
+ called. */
+ xdlclose (handle);
+
+ return 0;
+}
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